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Appl. Phys. Rev. 8, 041324 (2021); https://doi.org/10.1063/5.0062671 8, 041324
© 2021 Author(s).
The emergence of concentrator
photovoltaics for perovskite solar cells
Cite as: Appl. Phys. Rev. 8, 041324 (2021); https://doi.org/10.1063/5.0062671
Submitted: 07 July 2021 • Accepted: 11 November 2021 • Published Online: 15 December 2021
Priyabrata Sadhukhan, Anurag Roy, Payal Sengupta, et al.
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The emergence of concentrator photovoltaics
for perovskite solar cells
Cite as: Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671
Submitted: 7 July 2021 .Accepted: 11 November 2021 .
Published Online: 15 December 2021
Priyabrata Sadhukhan,
1
Anurag Roy,
2
Payal Sengupta,
3
Sachindranath Das,
1
Tapas K. Mallick,
2
Mohammad Khaja Nazeeruddin,
4
and Senthilarasu Sundaram
2,5,a)
AFFILIATIONS
1
Department of Instrumentation Science, Jadavpur University, Kolkata 700032, India
2
Environment and Sustainability Institute, University of Exeter, Penryn Campus, Cornwall TR10 9FE, United Kingdom
3
Department of Physics, Jadavpur University, Kolkata 700032, India
4
Group for Molecular Engineering of Functional Materials, Institute of Chemical Sciences and Engineering,
Ecole Polytechnique F
ed
erale de Lausanne, Valais Wallis, CH-1951 Sion, Switzerland
5
Electrical and Electronics Engineering, School of Engineering and the Built Environment, Edinburgh Napier University,
Merchiston Campus, Edinburgh EH10 5DT, United Kingdom
a)
Author to whom correspondence should be addressed: s.sundaram@exeter.ac.uk
ABSTRACT
The emergence of high-efficiency photovoltaic research is undergoing intense study and is technologically desirable to meet sustainable energy and
environmental demand. However, every single solar cell has a theoretical power conversion efficiency limit, and, thus, without compromising the
cost, the power conversion efficiency enhancement of a solar cell is highly challenging. As a convenient solution, concentrating photovoltaics can focus
sunlight onto an extremely high-efficiency solar cell integrating various optics. Concentrating photovoltaics use optical devices that collect and redirect
the light toward the smaller photovoltaic cell and reduce the demand for the mined elements required for the solar cell fabrication. The research inter-
est from the photovoltaic community has concentrated on organic-inorganic hybrid halide perovskite absorbers, and nowadays, perovskite solar cells
manifest their outstanding contribution among the low-cost photovoltaic technologies. Inevitably, large-area perovskite solar cells suffer a lotwith
their poor stability, hindering their commercialization pace. Thus, the implementation of concentrating photovoltaic technology in perovskite solar
cells demonstrates an inherent advantage using a smaller size solar cell. This review provides an overview of concentrating photovoltaic technology
implementation, including their recent research and development portfolio, their economic benefits in combination with inexpensive optical elements
and tracking systems, limitations, challenges, and relative scope of the future study, focusing on the emerging perovskite solar cell technology.
Published under an exclusive license by AIP Publishing. https://doi.org/10.1063/5.0062671
TABLE OF CONTENTS
I. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
II. EVOLUTION OF HYBRID PEROVSKITE SOLAR
CELLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
III. CONCENTRATOR PHOTOVOLTAIC . . . . . . . . . . . . . . 4
IV. HYBRID PEROVSKITES IN CPV . . . . . . . . . . . . . . . . . . 7
V. RECENT ADVANCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
VI. STABILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VII. COST ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
VIII. PERSPECTIVE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
IX. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
I. INTRODUCTION
Exploring a sustainable, nonpolluting energy source that can tar-
get to achieve at low cost is also becoming a hot topic of research
interest. Despite its jaw-dropping success in laboratory-scale produc-
tion, fabrication for a large area flat plate organic-inorganic hybrid
perovskite solar cell (PSC) is still a technologically challenging job. The
highest reported power conversion efficiency (PCE) for planner perov-
skite solar cells is over 25%.
1
That is for tiny size cells of an active area
of a few mm
2
. Increasing the area to the cm
2
range pushes the PCE
over 20% (Refs. 2and 3)[Fig. 1(a)]. As the active area is enlarged fur-
ther, the PCE drops rapidly due to inefficient film deposition with the
pores, grain boundaries, increasing resistance of the transparent con-
ducting oxide, etc.
4
A larger cell area also increases the probability of
moisture-induced degradation from the larger contact surface.
Appropriate encapsulation can be beneficial, but that adds extra cost
to the complete module. On the other hand, light conditioning techni-
ques like concentrating photovoltaic (CPV) can address the scalability
problem. This technique is not new, but it failed to compete with flat
Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-1
Published under an exclusive license by AIP Publishing
Applied Physics Reviews REVIEW scitation.org/journal/are
plate solar cells on the economic ground. It holds a share of only
350 MW out of 230 000 MW of total solar photovoltaic installed glob-
ally until 2015.
5
That is less than 0.2%. The majority of these CPV
panels were installed during 2010–2012. After that, a drastic drop in
the flat plate silicon solar cell cost gradually outsmarted the solar con-
centrator modules [Fig. 1(b)].
6
The theoretical limit of PCE for a single-junction solar cell under
concentrated light is above 40%. For most CPV systems, multi-
junction solar cells like dual, triple or quad junction solar cells are
used.
7–10
These solar cells are composed of group III–V components
such as doped indium gallium arsenide, aluminum gallium indium
phosphide, gallium arsenide etc.
2,11–13
Theoretically, the PCE of a
triple-junction solar cell can reach up to 60%.
11
Quad junction solar
cells can go even further. A triple-junction solar cell can practically
deliver up to 17% higher electricity under concentrated sunlight.
1
Figure 1(c) illustrates the PCE increment of powerful solar cell tech-
nologies under concentrated light. The highest reported PCE is for a
six-junction cell, which has achieved 47.1% under 143 suns; that is
20% higher than the non-concentrated condition.
14
However, these
multijunction solar cells are costly due to their complicated architec-
ture and complex fabrication process. The cost added by these expen-
sive high-efficiency cells and concentrator optics makes the whole
system very costly. Besides, two-axis precise solar trackers must get the
best performance out of the CPV cell by always directing it toward the
sun. All these things together escalate the total cost of a single module.
This cost somehow competed with flat-panel silicon solar cells in ear-
lier days. The heart of the CPV systems, the multi-junction solar cells,
could not cope with the silicon solar cells in terms of price reduction
with time. Thus, despite being a wonderful technology, CPVs are still
a minor in renewable energy options for their expensive design.
Comparatively, single-junction crystalline silicon (c-si) solar cells are
much cheaper. c-Si based single-junction solar cells are also used in
some low or medium concentration photovoltaic systems. The module
shows a better acceptance angle in such an arrangement, requiring a
less precise tracking system. A single junction crystalline solar cell
under a concentrator delivers 27.6% PCE only below 100 suns, which
is around 6% higher than a flat plate system.
15
This increment of PCE
under concentrated sunlight light touches an even higher value of
FIG. 1. Illustration of the tremendous growth of PSCs in terms of their PCE, cost and research interest over other PVs. (a) Evolution of PCE of PSC devices with device area.
3
Reprinted with permission from Li et al., Adv. Funct. Mater. 10, 2008621 (2020). Copyright 2020 John Wiley and Sons. It is clear that with a bit of scale up the active area,
PCE drops significantly for single PSC devices. (b) Year-wise Levelized cost of electricity (LCOE) produced in concentrated solar power (solar thermal power system) (CSP),
concentrated photovoltaics (CPV) and normal photovoltaics (PV) systems show higher cost per watt for concentrated solar electricity.
5
(c) Improvement of PCE of some popu-
lar solar cell technology under concentrated light. 3J and 4J denote triple junction and quad junction solar cells, (d) Comparative graph of number of articles published per year
shows PSC based CPV systems received limited exposure. Data are taken from Ref. 23.
Applied Physics Reviews REVIEW scitation.org/journal/are
Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-2
Published under an exclusive license by AIP Publishing
9.7% for gallium arsenide (GaAs) based solar cells.
1
However, GaAs
cells are expensive, limiting their deployment in applications requiring
a high power/weight ratio like space exploration. Dye-sensitized solar
cells (DSSC), the predecessor of perovskite solar cells, have also been
tested for application under solar concentrator.
16
In 2008, Youzhuan
et al. tested wavelength-selective photonic crystals as the solar concen-
trator on a DSSC cell.
17
They came out with a remarkable five-time
increment of power output from the DSSC cell. The photonic crystals
even worked better than the aluminum foils concentrator in module
stability. It was found that integrating a luminescent concentrator with
a DSSC can yield many-fold improvements in its power output.
18
Inspired by this work, Sacco et al. measured a DSSC with an optical
concentrator in outdoor condition and reported a linear photocurrent
up to 1.5 suns.
19
After that, photocurrent kept increasing in a non-
linear fashion before saturating at 5.5 suns. A 67% increment of PCE
for a semi-transparent DSSC under a low concentrator with 3con-
centrations is reported by Prabhakaran et al.
20
However, DSSCs are
still far from the commercial standard of PCE, but they have paved the
path for promoting PSCs in CPV. Thanks to its low-cost design, PSC
can be a technologically and commercially viable solutions for low-
cost CPV systems. The experimental setbacks of preparing high-
efficiency large-area PSC can be eliminated here as CPVs uses small
solar cells at higher illumination. However, the extra heating due to
concentrated solar illumination may negatively impact performance
and stability. The effect of high illumination is also another point of
concern here. Besides, charge carrier mobility and carrier lifetime in
the hybrid perovskites at higher illumination are the other figures of
merit to be considered before successfully incorporating PSC in CPVs.
However, a recent report has shown that the hybrid perovskites exhibit
stronger photoluminescence yield under concentrated illumination up
to several thousand suns. This result draws a silver line in the practical
feasibility of hybrid perovskite-based concentrator photovoltaics.
21
Later, 23.6% of PCE was achieved at 14 suns equivalent illumination
by a British group of researchers.
22
Though this number is not aston-
ishingly high, it presented a proof of concept of using PSCs in low-cost
CPV. We also need to remember that this is the PCE reported for
single-junction PSC devices, while most commercial CPV devices are
based on a multi-junction structure. A futuristic multi-junction PSC
will change the game with its incredibly low-cost design than group
III–V semiconductors. PCE of a solar cell says how much percentages
of the total incident sunshine can be converted into electricity.
Therefore, higher PCE means the solar cell will produce more electric-
ity from a given area. In other words, for the same amount of area,
more solar power can be converted to electricity. This would reduce
the total system cost, as smaller numbers solar module will be
required. In addition, installing a solar setup holds a significant per-
centage of the total system cost. As installation is charged mostly based
on the setup area, higher PCE modules reduce the cost. In CPV, multi-
ple optical elements are used for light conditioning. Generally, a solar
module contains multiple such small systems placed side by side. If
the individual solar cells’ PCE is increased, even 1% indicates a signifi-
cant increment of power production from a module will be accom-
plished. Also, concentrator solar cells work at higher PCE than direct
incidence solar cells, which means more solar electricity can be gener-
ated from a similar module size. Therefore, CPV can still have several
advantages to lead it again in the global solar power markets, especially
in the regions with a high direct normal incidence (DNI) of sunlight.
However, the cost per watt of solar concentrator modules must be
competitive with the flat plate arrays. PSCs can be the key here. Still,
one more challenge is there. Though flat plate PSCs compete with sili-
con counterparts side-by-side in terms of PCE, it is surprising that
PSC is explored much less for CPV. Figure 1(d) shows the number of
publications related to PSC and PSC is CPV. Research works on CPV-
based PSC is minuscule until.
23
This review has provided an overview
of recent developments, progress, and concentrator-based PSC tech-
nology and their technological and commercial viabilities for futuristic
energy solutions.
II. EVOLUTION OF HYBRID PEROVSKITE
SOLAR CELLS
BaTiO
3
was the first perovskite to show photocurrent under light
illumination back in 1956.
24
It was found that the internal field in
these perovskites has something to do with photocurrent generation.
The polarization induced strong internal field can separate the photo-
generated carriers. This mechanism can produce voltage higher than
the bandgap leading to higher PCE surpassing the theoretical limit of a
p-n junction solar cell.
25
Inspired by this pioneering work, several
other oxide perovskites were investigated for photovoltaic applica-
tions.
24,26–28
However, the result did not come as anticipated.
Maximum obtained photo conversion efficiency lay below 1%.
29
Soon
after this, it was understood that oxide perovskites are not a favored
option for photovoltaic applications. Another class of perovskites are
the halide perovskites, which contains halide anions in place of oxide
ones and are represented by the ABX
3
chemical structure. The crystal
structure of these materials is cubic perovskite, as shown in Fig. 2(a).A
slight buckling with the constituent atoms can form several deformed
perovskite structures, leading to a drastic change in the material’s opti-
cal, structural, and electrical properties. In alkali-based halide perov-
skites, a monovalent alkali metal ion (Cs
þ
) places in the A-site. In the
case of organic-inorganic hybrid perovskites (OIHPs), an aliphatic
ammonium cation (CH
3
NH
3
þ
) and formamidinium (CHN
2
H
4
þ
)
FIG. 2. Graphical visualization of general ABX
3
perovskite structure with A repre-
senting organic cation, B representing metallic cation, X representing halogen, and
their implementation in different PSC device architecture. (a) Lattice structure of
ABX
3
type perovskites. (b)–(d) Three main PSC structures namely, regular planner,
inverted planner and mesoporous.
Applied Physics Reviews REVIEW scitation.org/journal/are
Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-3
Published under an exclusive license by AIP Publishing
occupies the A-site, and a divalent metal cation (Pb
2þ
,Sn
2þ
,Ni
2þ
,
etc.) sits at B-site.
25
A halogen anion (I-, Br-, Cl-) occupies the X-site
position. Halide perovskites with an organic cation at the A-site posi-
tion are commonly called organic-inorganic hybrid perovskites. The
ionic radius of the halide ions I-, Br- and Cl-ions are 2.07, 1.84, and
1.67 A
˚, respectively. Even with the same A-site cation, the tolerance
factor would vary significantly with a halide anion change. Some of
the well-performing organic-inorganic hybrid perovskites are
Methylammonium lead iodide (CH
3
NH
3
PbI
3
or MAPbI
3
), formami-
dinium lead iodide (CHN
2
H
4
PbI
3
or FAPbI
3
), formamidinium tin
iodide (CHN
2
H
4
SnI
3
or FASnI
3
) or the mixed halide perovskites like
CH
3
NH
3
PbI
3-x
Br
x
and mixed cation perovskite like FA
1-x
MA
x
PbI
3-y
Br
y
,
etc.
25,30–32
The lead content in most halide perovskites is an
environmental threat. Though lead content is minimal (0.001%) com-
pared to the cell’s total weight,
33
this is also not desired for sustainable
deployment. Different lead-free perovskites with tin (Sn),
34,35
germanium
(Ge), bismuth (Bi),
36,37
etc., are also being investigated for photovoltaic
applications but, so far, none of them except the tin-based ones have per-
formed with the considerable outcome. However, Sn-based perovskites
like CH
3
NH
3
SnI
3
or FASnI
3
are quite unstable.
38
Another Sn-based
perovskite, CsSnI
3
exhibits comparatively better stability but lacks higher
PCE understanding due to its deficient carrier mobility and high
minority carrier effective mass.
39
Recently, a Pb-Sn mixed metal halide
perovskite (FA,MA)(Pb,Sn)(I,Br)
3
have reached 20% PCE.
40
Hybrid perovskites can be deposited in a single or multilayer
structure leading to lower-dimensional forms.
41
Ageneralizedformula
as (RNH
3
)
2
A
n-1
B
n
X
3nþ1
can be indicated for OIHPs. Where R is a
large organic cation, A is a small organic cation, B is a metal cation,
and X is the halide anion. “n” defines the inorganic sheet thickness; as
n increases, the material changes dimensionality from 1D toward a
higher dimension. Hence, n ¼1represents a three-dimensional (3D)
OIHPs. The lower dimensionality of two-dimensional (2D)
perovskites gives them better stability due to the highly oriented nature
of the film and the large cation’s hydrophobicity. Nevertheless, this sta-
bility comes at the expense of poor photovoltaic performance for their
highly directional carrier transport and wider bandgap. Thus, 2D
hybrid perovskites are mainly used as an interfacial layer to reduce the
recombination on top of 3D perovskite.
42–44
A PSC device’s multilayer structure comprises a front electrode,
an electron transport layer (ETL), a perovskite absorber layer, a hole
transport layer (HTL), and the back electrode. Figures 2(b)–2(d) shows
the three primarily used PSC device structures. Tremendous research
efforts on these layers and the perovskite itself have improved photo-
voltaic performance and stability considerably. PCE has reached the
crystalline silicon solar cells standard, while the cell’s lifetime has been
improved from few hours to few thousand hours. These values are still
inferior to the commercial solar cells but significant enough to con-
sider PSCs in advanced photovoltaics like CPV. A PSC device’s life-
time is represented as the number of hours the cell can perform with
at least 80% of its initial PCE. The lifetime in the dark denotes storage
of the PSC device in the dark in between two characterizations, and a
lifetime in light signifies continuous sunlight exposure. Table I sum-
marizes hybrid perovskite-based solar cells’ evolution in terms of both
performance and stability.
III. CONCENTRATOR PHOTOVOLTAIC
The concentrated light reaching the solar cell increases energy
production several times. As mentioned earlier, based on the light illu-
mination intensity, it focuses on the solar cell. The concentrators may
be classified as low concentration systems, medium concentration sys-
tems and high concentrator systems. Low concentration systems are
usually simple in their design, manufacture and operation. These sys-
tems have a concentration factor of less than 10. Due to its versatility
in applications and geometries, a type of low concentrator—the
TABLE I. Important milestones in improving the PCE and lifetime of PSC. MA: methylammonium, FA: formamidinium, EH44: 9-(2-ethylhexyl)-N,N,N,N-tetrakis(4-methoxy-
phenyl)-9H-carbazole-2,7-diamine, PCBM: phenyl-C
61
-butyric acid methyl ester, BCP: bathocuproine, and AVA: ammonium valeric acid.
Material Year Major improvements PCE (%)
Lifetime
in dark (hours)
Lifetime in
light (hours) Reference
CH
3
NH
3
PbI
3
2011 6.5 0.17 0.17 45
CH
3
NH
3
PbI
3
2014 Spiro-oMeTAD used as HTL 11.6 14 14 46
CH
3
NH
3
PbI
3
2015 NiMgLiO used for HTL and
PCBM/TiNbO
x
/Ag for ETL
16.2 1000 1000 47
CH
3
NH
3
PbI
3
2016 Graphene oxide/spiro-oMeTAD
used as HTL
18.19 400 4 48
CH
3
NH
3
PbI
3
2018 NiO as HTL and
PCBM/ZnO/Al as ETL
17.3 1050 49
(Cs
0.02
FA
0.98
PbI
3
)
0.97
(MAPbBr
3
)
0.03
2018 Chlorine doped TiO
2
as ETL 21.7 250 250 50
FAMACs 2018 EH44/MoO
x
/Al as HTL
and SnO
2
as ETL
18.5 1500 1000 51
(FA
0.83
MA
0.17
)
0.05
Cs
0.95
Pb(I
0.9
Br
0.1
)
3
2019 PCBM/BCP/Cr/Cr
2
O
3
/Au as ETL 19.8 1800 52
(HOOC(CH
2
)
4
NH
3
)
2
PbI
4
/
CH
3
NH
3
PbI
3
2017 2D/3D perovskites with
carbon electrode
used to increase stability
14.6 12 000 300 53
(5-AVA)
x
(MA)
1x
PbI
3
2017 14.02 8760 1000 54
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Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-4
Published under an exclusive license by AIP Publishing
compound parabolic concentrator (CPC) is used in the quiet and
medium temperature range. Commonly seen solar systems are flat
plate solar cells directly illuminated by the incident solar irradiation.
The standard intensity of illumination is 1 sun or 1000W/m
2
.The
whole illuminated surface is the active region of the solar cells. In
CPVs, the incident light is first focused with a lens or mirror arrange-
ment to the point of illumination, where illumination intensity can be
much higher than 1 sun or 100 mW/cm
2
. The solar cell is placed on
that focal point. As the focused beam is very narrow, the active area of
the cells can be minimal. As the optical arrangement’s focal point
moves with the sun, the whole system needs to be aligned all-time
with the solar trajectory course. For this, an active solar tracking sys-
tem is employed. So, the three main components of a CPV system are
as follows:
(a) The optical collector can be a lens or a mirror to focus the
incident light.
(b) The receiver is a solar cell or an array of solar cells designed
to perform under high illumination.
(c) The solar tracking system keeps the whole system aligned
with the sun to ensure vertical sunlight illumination on the
optical collector.
Different reflecting, refracting, and luminescent optics are used
for the concentrator optics,
55
depending on the application area,
required concentration, and many other factors. Figure 3(a) outlines
optical concentrators’ different classes depending on their geometric,
optic, concentration or tracking mechanism. Figure 3(b) shows a flat
plate solar cell. For high concentration, reflective and refractive type
concentrators are mostly used.
55
A parabolic mirror is the most widely
used reflective type optical concentrator [Fig. 3(c)]. Parabolic trough
type reflector can provide concentration up to 200.
56,57
A convex lens
is used as a refractive concentrator [Fig. 3(d)]. Another widely adopted
concentrator is a Fresnel lens that works like a standard refractive lens
and can deliver up to 2000 suns. Fresnel lens is a periodic
Arrangement of some concentric rings, each acting as a lens element.
The whole system can focus light to a tiny spot but stay much less
bulky than a conventional convex lens. One distinct advantage of
this optical system is that each facet’s shape and orientation can be
tailored to adjust the focused light’s spatial uniformity.
58
Sometimes, both reflective and refractive mechanisms focus on
optics [Fig. 3(e)]. This optical arrangement makes use of total inter-
nal reflection. Some novel approaches like butterfly wings
59
are also
explored recently to reduce the weight and boost the specific power
density of the CPV modules.
The ratio between the area of the aperture of the optical collector
and the solar cell’s active region is called the geometrical concentration
factor (C
g
). It signifies the ratio between light intensity at the optical
collector and the solar cell’s surface. Depending on the concentration
factor, CPV can be categorized into three types namely, low-
concentration photovoltaics (LCPV), low-concentration photovoltaics
(MCPV), high-concentration photovoltaics (HCPV) for C
g
<40, 40
<C
g
<300, 300 <C
g
<1000, respectively.
10
Several other classifica-
tions are also made based on focus type (linear focus, point focus,
micro-focus, etc.), solar cell type (multi-junction, single-junction, etc.).
Table II shows the advantages and disadvantages of a commercial
CPV system. Some of the disadvantages of commercial CPV systems
are addressed in recent research articles. For example, hybrid CPV/PV
architecture has been introduced to collect both direct and indirect
light.
60
Bifacial PV panels are also tested in the CPV system to use light
coming from all directions. However, these systems employ two sets of
solar cells to collect light from all sources and directions, and thus it
adds extra cost to an already expensive CPV system. To make CPV
FIG. 3. Fundamental features of concentrator optics. (a) Different classes of concentrator optics. (b) A solar cell without concentrator. Some common types of concentrator (c)
reflector type, (d) lens based refractor type, and (e) reflector–refractor combined.
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systems suitable for rooftop installation, Jared et al. has introduced
quasi-static microcell CPV system that eliminated the full-scale track-
ing system.
61
However, the system contains a micro-alignment system
forthesolarcells.
Regular CPV system uses a sizeable optical concentrator module
to focus the beam on the solar cell underneath. It can also introduce
several complexities like uneven focusing of light and the subsequent
inhomogeneous solar cell temperature profile. Besides, the intense
beam sets the solar cell temperature very high, requiring a heavy heat
sink mechanism to keep the cell temperature within the specified limit.
These systems are highly susceptible to direct sunlight, and slight mis-
alignment with the sun shifts the focus point from the desired
location.
So, a precise solar tracker is also required. The whole system
becomes very bulky and heavy. To reduce the high alignment preci-
sion requirement and address all these complications, thin-film micro-
CPV was introduced.
62–64
Here, the entire system is broken into ‘n’
numbers of small concentrator PV systems [Fig. 4(a)]. The advantage
is that the size of both the optical element and the solar cells are
smaller, reducing the technological complexities in fabricating large-
size optical elements or solar cells.
65,66
This architecture improves the
temperature profile’s homogeneity on the solar cell plane, which helps
dissipate the heat more efficiently and reduces thermal stress.
67,68
The
smaller solar cells suffer less from the series resistance loss as the
amount of current from a single cell is significantly reduced.
66,69
Smaller cells also give the freedom of organizing the array in the
desired series/parallel combination to best suit the voltage and current
requirement of the subsequent loads. As PSC systems have many
interfaces combined with electron transport, hole transport, perov-
skite, and back contact, incoming light intensity could influence the
devices’ electronic properties. When a solar concentrator is coupled,
incoming light’s intensity becomes higher. Figure 5 illustrates the dif-
ferent charge transport processes of a dye sensitized solar cell under
plain light and concentrated light. In a bare solar cell, the electron
TABLE II. Advantages and disadvantages of commercial CPV systems.
Advantages of commercial CPV Disadvantages of commercial CPV
High-efficiency due to a logarithmic increase of the
open-circuit voltage with light intensity
Requires sun tracking
High energy output in locations with a high fraction of direct
irradiance
Cannot collect diffuse irradiation
Logarithmic decrease of the absolute value of the negative
temperature coefficient of open-circuit voltage (V
OC
) with light
intensity
Limited deployment—mainly in regions with high direct
average irradiation and for space—constrained or very
high-efficiency applications
Less semiconductor material usage than flat-plate Not suitable for rooftop applications
Low capital expenditure for manufacturing, production
facilities and infrastructure
Higher system cost per watt than flat-plate PV
Maximum energy yield per land area Higher impact of soiling
FIG. 4. Schematic illustration of the advantages originated from CPV integrating into a PV cell. (a) Structure of a micro-CPV system showing light concentration using an array
type optical element at the top. A solar cell array is placed at the bottom of the fixture. The CPV system uses a single lens of local length f, while the micro CPV system uses
N
2
number of miniaturized solar cells with its miniature lens of focal length f/N. (b) Advantages of CPV systems over flat plate solar cells.
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generation is less light intensity. More electrons are generated when a
concentrator is coupled,
70
seen from Fig. 5(b). Even though the scaled-
up device generates and transports more electrons, the active area is
four times larger than the small device. The concentrator-coupled
device’s electron transport is similar to the scaled-up device with 4
lesser active area.
IV. HYBRID PEROVSKITES IN CPV
Dye-sensitized solar cells (DSSC) made the foundation stone for
flat plate hybrid PSCs.
25
The performance of DSSC solar cells under
concentrated light showed the possibility of doing the same with PSC
also. From the low charge mobility of these materials, it was previously
expected that the high charge density generated from the high photon
flux of the concentrated light would cause too much recombination
that will make these cells incapable of working under high illumina-
tion. Nevertheless, in 2014, Law et al. showed some exciting results
from their experiments with different DSSCs and PSCs under higher
light intensity than expected.
71
They studied some organic and disor-
dered semiconductors, such as DSSCs with standard dyes, polymer
and MAPbI
3
perovskite-based solar cells. Their investigation showed
that PSCs could produce photocurrent density (J) up to 0.5 A/cm
2
under 50 sun equivalent light intensity. The cells can survive until 60 h
with just 8% photocurrent degradation. Above 50 suns equivalent
light, charge accumulation and recombination started playing a more
significant role in short circuit current. At higher illumination, short
circuit current density (J
SC
) increased. To exclude the effect of Ohmic
voltage drop due to a series resistance of the substrate and the other
connecting wires, the authors calculated actual short circuit current
density J
SC
. This approach helped to compare the J
SC
at different irra-
diation, maintaining the same internal electric field. The results are
shown in Fig. 6. This study drew the silver line for the futuristic perov-
skite based LCPV systems.
V. RECENT ADVANCES
Wang et al. had performed a comprehensive study on PSC based
CPV systems with a list of perovskite absorber materials.
22
The list
contained pure cation perovskite like methylammonium lead iodide
(MAPbI
3
) and mixed cation variants like forrmamidinium–cesium
lead halide (FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
) and triple cation formamidinium-
methylammonium-cesium lead halide (FA
0.79
MA
0.16
Cs
0.05
PbI
2.7
Br
0.3
),
among which FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
was the best performing compo-
sition. PCE of the MAPbI
3
and the FA
0.79
MA
0.16
Cs
0.05
PbI
2.7
Br
0.3
FIG. 5. Schematic illustration of the light illumination (a) bare, (b) with concentrator, for a similar DSSC device.
70
Reprinted with permission from Selvaraj et al., Mater. Lett.
222, 78. (2018). Copyright 2018 Elsevier.
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started to drop only after 1.2 suns and 2 suns light concentrations,
respectively. However, the FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
absorber-based cell
revealed good performance at a high irradiance level. Key data of their
findings are shown in Figs. 7(a)–7(c). The cell architecture was
designed as FTO/SnO
2
/FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
/spiro-OMeTAD/Au
which delivered a boosted maximum PCE of 23.6% at 14 suns from
21.1% at 1 sun [Fig. 7(a)]. Stabilized power output (SPO, efficiency
after holding the cell at the maximum power output voltage for 60 s)
reached 22.6% at 14 suns. The cells were not actively cooled in the
measurement process, leading to cell temperature reaching 38 C.
With increasing irradiation, both the open-circuit voltage (V
OC
)and
short circuit current (I
SC
)increased.Asexpected,I
sc
followed a linear
profile with illumination intensity before becoming flat after 50 suns.
V
OC
followed a semi-logarithmic increment as predicted from the
diode equation and reached a peak value of 1.26 eV at 53 suns
[Fig. 7(b)]. Nevertheless, the overall cell PCE started to decline after 14
suns because of fill factor (FF) deterioration [Fig. 7(c)]. Increasing V
OC
could overcompensate the decreasing FF until 14 suns. To investigate
this ‘FF roll-off, the authors measured each solar cell layers’ resistance
by making different sub-cells like FTO/Au, FTO/SnO
2
/Au and FTO/
SnO
2
/spiro-OMeTAD/Au. Spiro-OMeTAD introduced the maximum
resistance in the charge extraction process. The authors assigned the
effect of the charge extraction layer’s series resistance to be held
responsible for FF’s declination. Now reduction of series resistance
became evident to improve the PCE and promote this perovskite for
CPV. This study is supported by other studies as well. Instead of mixed
halide e perovskites, the suitability of MAPbI
3
and Cs
0.15
FA
0.85
PbI
3
perovskites in CPV were also studied.
72
Low trap density inside
Cs
0.15
FA
0.85
PbI
3
than MAPbI
3
made bimolecular recombination to be
predominant. This is advantageous for Cs
0.15
FA
0.85
PbI
3
to perform
better for a long exposure of concentrated light and attain around 18%
PCE between 0.5 and 3 suns [Fig. 7(d)]. This PCE was finally reduced
to 16% with 60% FF at 13 suns of concentrated light. No significant
drop in performance was observed even after 6 h of exposure. MAPbI
3
showed 17.8% PCE at one sun, but it could not perform better at
higher illumination intensity, just like the result observed by Wang
et al. At 1 sun, both the MAPbI
3
and Cs
0.15
FA
0.85
PbI
3
showed similar
performance and 18% PCE. However, as the illumination intensity is
increased, MAPbI
3
quickly nose-dived below 10% at 13 suns.
However, unlike the other reports, V
OC
followed a linear profile of
even 1000 suns [Fig. 7(e)]. FF is one of the limiting parameters to
reduce efficiency at high illumination, as discussed earlier. MAPbI
3
performed worst here. Upon increasing the light concentration from 1
sun to 10 suns, FF for MAPbI
3
solar cells reduced from 74% to just
41%, while Cs
0.15
FA
0.85
PbI
3
managed to offer 60% from the same ini-
tial value as MAPbI
3
[Fig. 7(f)]. To explain this, we need to look at
these two perovskites’ carrier lifetime at a different concentration or
carrier density. Higher carrier lifetime allows better charge collection
efficiency, leading to higher PCE. Joel et al. calculated the carrier
lifetime vs charge density of the two materials.
72
As we can see in
Fig. 8(a),thecarrierlifetimeofMAPbI
3
is higher than that of
Cs
0.15
FA
0.85
PbI
3
until one sun, but it becomes smaller after that.
Higher recombination order (R) for MAPbI
3
indicates the trap assisted
recombination like monomolecular recombination to be predominant
in this material as the charge density increases with light concentra-
tion. Previous work also calculated that the monomolecular recombi-
nation rate constant of MAPbI
3
is three times higher than that of
mixed cation perovskites.
22
This discussion justifies the poor perfor-
mance of MAPbI
3
at higher concentrations. A thorough theoretical
study on the recombination mechanism came up with a deep under-
standing of the relation between the recombination mechanism and
high irradiance behavior. The authors modeled a hypothetical solar
cell using a 300 nm thick prototypical lead iodide-based hybrid perov-
skite film with a bandgap of 1.6 eV and 100% external quantum yield.
To form the rate equation, monomolecular, bimolecular and Auger
recombination, and charge extraction from the active layer, were con-
sidered in simulation.
73
Bimolecular recombination is band-to-band
recombination, an intrinsic property of the material that cannot be
altered. Auger recombination takes part at a very high charge carrier
density.
74
This condition can show high illumination intensity by high
concentrating systems. Monomolecular recombination is trap medi-
ated Shockley-Hall-Read recombination.
73
Different recombination
mechanisms are illustrated in Fig. 9(a). As trap density depends on the
material processing protocol and device fabrication technique, it can
vary even for the same perovskite compositions processed differently.
The authors also considered all other layers of a thin-film solar cell
and used their simulation contribution. Using this model, this study
calculated J
SC
at different solar concentrations with a different combi-
nation of monomolecular, bimolecular and charge extraction rate con-
stant. J
SC
showed little dependence over monomolecular or
bimolecular recombination rate values below 100 suns [Fig. 8(b)]. This
is what was experimentally observed in some previous reports.
22,72
However, charge extraction showed heavy control over the J
SC
.The
charge extraction rate at 10
6
/sec can significantly alter the J
SC
vs con-
centration curve’s linearity even at 1 sun range [Fig. 8(c)]. The magni-
tude increment in charge extraction rate shifts the non-linear cut in a
J
SC
concentration to ten times higher position. However, both the V
OC
and FF showed high dispersion with monomolecular recombination
rate, as shown in Figs. 9(b) and 9(c). The simulated photovoltaic
FIG. 6. Current–voltage (JV) curve of a MAPbI3 perovskite-based solar cell under
different illumination intensities. The dashed line is the JV curve under 41 SE after
applying the correction for series resistance effect.
71
Reprinted with permission
from Law et al., Adv. Mater. 26, 6268 (2014). Copyright 2014 John Wiley and Sons.
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Published under an exclusive license by AIP Publishing
performance predicted a peak efficiency value of more than 30% near
100 suns, almost touching the Shockley–Queisser limit [Fig. 9(d)].
This leads to the deduction that traps assisted monomolecular recom-
bination and charge extraction efficiency from perovskite layers are
the two most crucial factors to define a PSC’s performance under high
illumination. The authors have also indicated that more than 30%
PCE can be achieved at 10 to 100 sun solar concentrations by improv-
ing the charge carrier lifetime to 10 ls. Aaesha et al. investigated this
FIG. 7. Comparison of different PV parameters by varying the solar concentration using CPV and perovskite active material. Evolution of (a) PCE, (b) V
OC
and (c) FF with solar
concentration for FTO/SnO
2
/FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
/spiro-OMeTAD/Au structure.
22
Reprinted with permission from Wang et al., Nat. Energy 3, 855 (2018). Copyright 2018
Springer Nature. (d)–(f) shows the comparative values of PCE, V
OC
and FF, respectively, as a function of light intensity for MAPbI
3
and Cs
0.15
FA
0.85
PbI
3
based solar cells.
72
Reprinted with permission from Troughton et al., J. Mater. Chem. A 6, 21913 (2018). Copyright 2018 Royal Society of Chemistry.
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Published under an exclusive license by AIP Publishing
using 2D simulation with physics-based TCAD, the effect of mobility,
band structure and surface recombination velocity in the hole trans-
port medium (HTM) of concentrator PSC.
75
The simulation was per-
formed on a planer type CH
3
NH
3
PbI
3-x
Cl
x
-based solar cells structure
with TiO
2
and spiro-OMeTAD as the electron and hole transport
layer. Their simulation predicted that large band offset between the
HTM–perovskite layer interface and the low mobility of the hole
transport medium are the key cause of high series resistance and limit-
ing PSC efficiency parameters under concentrated sunlight. Besides,
high surface resistance at the interface is also another part. V
OC
did
not show any dependence on carrier mobility of the HTM [Fig. 10(a)].
Figure 10(b) shows the FF vs concentration of this theoretical model
solar cell. As we can see, the curves resemble the earlier experimental
observation of decaying FF with increasing sunlight concentration. In
Figs. 10(b) and 10(c), when the carrier mobility was set to 2 10
4
cm
2
/V s, both FF and PCE of their model solar cell started to decline
as the light concentration was increased from one sun to a higher
value. However, as the mobility value was increased to 2 10
1
cm
2
/
V s, FF switched fr om decaying to slowly increasing profile with light
intensity like the previous work. As FF is the key to tune the PCE of
the PSC at a high light intensity, PSC efficiency also started to increase
following FF. PCE rose from 23.3% at 1 sun to 26.5% at 100 suns. This
theoretical study has provided a deeper insight into the internal mecha-
nism of the charge dynamics at different illumination and shown a path
for redesigning the PSC architecture with efficient HTM to boost its per-
formance at a high concentration of incident light. Later, a combined
optoelectronics model was used to explore the PSC’s behavior in con-
centrated irradiance and subsequent elevation of temperature.
72
APSC
wasfirstdefinedasalayeredstructure,asshowninFig. 10(d).Cesium
formamidinium based mixed halide (CsFAPbIBr) was used as the mod-
el’s photovoltaic layer. The generalized transfer matrix method was
employed for optical modeling of the virtual PSC device. This model
provided the field distribution with the different layers and the device’s
interfaces,whichwasusedtolookintothedevice’sopticalbehaviorat
different layers. The calculated J
SC
[Fig. 10(e)]andV
OC
[Fig. 10(f)]fol-
lowed a linear pattern and semi-logarithmic pattern, respectively, with
the irradiation level. PCE of the PSC at 1 sun irradiation is 22.46%
which topped to 24.93% at 40 suns. Overall, the PSC’s simulated perfor-
mance under concentrated light revealed an excellent match with previ-
ous experimental result.
22
Loss of PCE above 40 suns was attributed to
the saturation of absorption of light by the perovskite layer. All the
above studies were performed on a bare solar cell without an actual opti-
cal concentrator unit. This setup lacked the testing of perovskite-based
concentrator solar cells in real concentrator architecture and could not
FIG. 8. Comparison of charge carrier factor for two different perovskites under different solar concentration. (a) Charge carrier lifetime vs carrier density of the MAPBI
3
and
Cs
0.15
FA
0.85
PbI
3.72
Reprinted with permission from Troughton et al., J. Mater. Chem. A 6, 21913 (2018). Copyright 2018 Royal Society of Chemistry. Dependence of J
SC
on
the solar concentration for different (b) monomolecular recombination rate and (c) charge extraction rate.
73
Reprinted with permission from Lin et al., Adv. Sci. 5, 1700792
(2018). Copyright 2018 John Wiley and Sons.
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show concentrator optics’ effect on the device performance. Recently a
multi-institutional group led by Hasan Baig addressed this issue. They
investigated the feasibility of double anion triple cation hybrid perov-
skites (FAPbI
3
)
0.875
(MAPbBr
3
)
0.125
(CsPbI
3
)
0.1
) solar cell in low concen-
tration micro CPV system.
76
This perovskite has already been proven to
be a very efficient perovskite material in flat plate solar cells.
40,72,77
Baig
et al. investigated its possible application in CPV. Most of the previous
experimental studies used PSC of an active area of the order of 1mm
2
.
The authors used a 9 mm
2
PSC for their experiment in a real working
environment with an optical concentrator of a kaleidoscope with a trun-
cated pyramid geometry. The entry aperture is a breaking– symmetry
top of 12 12 mm
2
and an exit aperture area of 3 3mm
2
. Digital
photograph of the unit is depicted in Figs. 11(a) and 11(b).Besides,they
extended their work to a more practical approach by exploring the effect
of non-perpendicular incidence of light and the elevated temperature
from concentrated sunlight. Here, the concentrator optics’ performance
wasalsoconsideredtogetaclearideaoftheCPVunit’sactualpower
output compared to the PSC. Power ratio (PR) was calculated from this
using the following equation:
PR ¼P
MAX
=PMAX ;(1)
where P
MAX is the maximum power obtained from the CPV unit
and PMAX is defined as the maximum power collected from the bare
PSC in similar conditions. This parameter provides information
about the performance of the concentrator. PR at a different inci-
dent angle showed minimal variation within 5inclination. This is
interesting as it eliminates the high precision tracker system
requirement for the CPV-based PSC unit. The figure of merit of an
optical concentrator is defined as the optical efficiency, which is the
fraction of incident light that reaches the concentrator’s focal point
after all the possible losses in the optical medium. Mathematically,
optical efficiency
îopt ¼1=CgIcpv
sc
=Ipsc
sc
;(2)
where Icpv
sc and Ipsc
sc are the short circuit current for the CPV and PSC
units, respectively. Cgrepresents the geometrical concentration factor.
îopt Also showed negligible depreciation within 5of normal inci-
dence. Dependence of PR and îopt on the incident angle in sunlight is
shown in Figs. 11(c) and 11(d). A high concentration of light supplied
an increased number of photons to the solar cell, grew photons, and
heated it. If a good heat management system is not deployed, the solar
cell temperature can reach well above its designated working tempera-
ture, and the cell is destroyed. Baig et al. observed how the PSC below
the concentrator module performs under natural heating from the
concentrated light. This showed the strong temperature dependence of
the V
OC
and I
SC
and the PCE. Higher temperature increases the dark
FIG. 9. Effect of different carrier recombination mechanisms and solar concentration level on the solar cell performance. (a) Different types of carrier recombination inside a
material. Dependence of (b) V
OC
, (c) FF and (d) PCE on solar concentration at different bimolecular and monomolecular recombination rate constant.
73
Reprinted with permis-
sion from Lin et al., Adv. Sci. 5, 1700792 (2018). Copyright 2018 John Wiley and Sons.
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current in the perovskite layer and reduces the V
OC
. This is what is
seen for other semiconductors also. However, the exciting thing is the
negative temperature coefficient of I
SC
.Generally,I
SC
increases with
temperature for most solar cells as most semiconductors exhibit
decreased bandgap.
78
Bandgap lowering allows more photon capture
and thereby higher I
SC
.
Nevertheless, perovskites showed lower I
SC
with a higher temper-
ature which is explained by their positive temperature coefficient of
bandgap with temperature.
79
The increased illumination performance
of the PSC followed other works quite well. However, contraryto other
literary works, the authors got a maximum PCE of 21.6% at 1.78 suns.
This value is relatively low in comparison to other reports.
22,71,72
FIG. 10. Comparison of different simulated PV parameters by varying the carrier mobility and solar concentration using CPV. (a) V
OC
, (b) FF and (c) PCE as a function of solar
concentration with different carrier mobility of the HTM layer. Substantial improvement of these performance parameters is seen when the carrier mobility is increased.
75
Reprinted with permission from Alnuaimi et al., AIP Adv. 6, 115012 (2016). Copyright 2016 AIP Publishing LLC. (d) structure of the modeled PSC device. Irradiance dependent
variation of J
SC
and V
OC
are depicted in (e) and (f), respectively.
81
Reprinted with permission from Cherif et al., J. Phys. Chem. Solids 135, 109093 (2019). Copyright 2019
Elsevier.
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Published under an exclusive license by AIP Publishing
Critical data from all the recent developments in concentrator-based
PSCs are summarized in Table III.
VI. STABILITY
Although, the phenomenal efficiency progress in MAPbI
3
-based
PSC has primarily been based on the properties and processing of the
perovskite layer. Inevitably, the cell performance limitations are now
linked with intrinsic and extrinsic parameters, and these hybrid perov-
skites are already known for their instability in certain conditions
41
[Fig. 12(a)]:
(1) Poor moisture stability of the perovskite, limiting device
lifetime.
(2) Toxicity of Pb, which could preclude some application areas for
the devices.
(3) Unstable structure of MAPbI
3
for UV-curing (high-energy light
sensitive).
MAPbI
3
is unstable at temperatures higher than 85Candfur-
ther decomposed at 200 C.
80
The broad tolerance factors further facil-
itate the perovskite crystal to tailor the original structure and
elemental compositions in perovskites. Choosing the correct halide
ions with the A and B cations in the perovskite structure is also
essential. Electronegativity is a fundamental chemical property that
can describe the capability of an atom to attract the electron density in
a chemical bond. Halide ion’s (X) electronegativity increases from I
to F
with the reduction of their ionic size. F
shows the most robust
bonding with the hydrogen atom of methylammonium (A-site cation)
and the Pb (B-site cation) compared to the other halogens, as shown
in Fig. 12(b). By forming a better charge transport across the B-X-B-X
network of ABX
3
perovskites, this type of perovskite structure enhan-
ces the electron mobility rate and sometimes restrict lead leaching.
The lower electronegativity difference fitted with Goldschmidt’s toler-
ance rule, which provides a value of 1 for a perfect perovskite structure.
The B-X bond can also lead to a lower bandgap, desired for visible and
NIR range optoelectronics.
82
However, for lead halide perovskites, the
tolerance factor ranges from 0.81 to 1.11. Tuning of the bandgap is a
critical parameter that also controls the stability of the perovskite
structure. Due to the toxic impact of Pb, Sn has been found as an alter-
native. However, Sn-based perovskites exhibit relatively red-shifted
bandgaps compared with their Pb-based counterparts. It is proposed
that a higher Pauling electronegativity of Sn (1.96) than Pb ions (1.87),
excels a smaller separation between the X(5p) states in the valence
band and the Sn(5p) states in the conduction band. Besides, the con-
centration of electron–hole pairs varies inside the perovskite layer
FIG. 11. Recent experimental study on CPV integrated-PSC. Digital photograph of the (a) bare PSC device with the view of the back electrode. (b) PSC attached with the opti-
cal concentrator element. (c) and (d) shows the effect of angle of incidence on power ratio and optical efficiency respectively.
76
Reprinted with permission from Baig et al.,
Sustainable Energy Fuels 4, 528 (2020). Copyright 2020 The Royal Society of Chemistry.
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governed by the halide ions migration.
83
Synergistic behavior of stabil-
ity, light absorption, and charge transport are fundamental parameters
of PSC development. In this regard, a multidimensional perovskite
structure is a promising method to solve those challenges based on
this strategy.
84
Additionally, MAPbI
3
shows a lattice phase change
near 55 C, which falls inside a real solar cell’s working temperature.
However, MAPbI
3
is also reported to perform well up to 80 Cinthe
solar cell if encapsulated from moisture. Thus, even in the CPV sys-
tem, and heating should not be a big problem if the cell temperature is
kept below that limit. Law et al. showed that MAPbI
3
in m-TiO
2
/
MAPbI
3
/spiro solar cell structure could work well up to the 63 suns.
The cell lost its photocurrent only at 0.2% per hour after the initial
drop and rose [Fig. 12(c)]. After 63 h, t he cell held 92% of its initial
photocurrent. However, FF has been one of the most significant
parameters to define the overall cell performance. This work did not
include any details of FF’s evolution over time in high illumination.
Among other charge transport layers like P3HT, DPPTTT or m-
Al
2
O
3
,m-TiO
2
and spiro-based solar cells were much more stable.
Nevertheless, this is not the case for formamidinium -based perov-
skites. From the material stability point of view, the cesium’s stabilizing
effect in the Cs-FA mixed cation-based perovskites makes them stable
than the previous one. But, It was also observed that the stability per-
formance of FTO/SnO
2
/FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
/spiro-OMeTAD/Au
solar cell structure was very poor.
22
The solar cells lost most of their
PCE in just 18 h of illumination under 10 suns. The resulting I-V data
are shown in Fig. 12(d).Wanget al. postulated that the instability was
due to the spiro-OMeTAD hole transporting layer. This assumption
was verified by the remarkable stability performance of a second
device that incorporated poly[bis(4-phenyl) (2,5,6-trimethylphenyl)
amine] (PTAA) instead of spiro. Also, the electron transport later
SnO
2
was coated with 4-(1,3-dimethyl-2,3-dihydro-1H-benzimidazol-
2-yl)-N,N-diphenylaniline (N-DPBI)-doped phenyl-C61-butyric acid
methyl ester (PC
61
BM). The cells could retain 91% of their initial PCE
after 150 h [Fig. 12(e)] of light soaking at 10 suns concentrated light.
That also went well with the spectroscopic and thermo-gravimetric
stability analysis. After 370 h, the cell presented 80% of its initial PCE.
However, a good thermal dissipater was used to keep the cell tempera-
ture to 30 C for this low solar concentration level. As discussed earlier,
breaking down the whole system into an array of micro-systems would
help improve thermal management. The total current will also be
divided into parts as the cells are made smaller, which would reduce
the impact on series resistance at the same time. In a comparative
work, both MAPbI
3
and Cs
0.15
FA
0.85
PbI
3
performed well until 950 h
of light soaking under 1 sun
72
[Figs. 12(f) and 12(h)]. However, under
13 suns, MAPbI
3
loses 50% of its initial PCE along with FF and J
SC
only in few hours [Fig. 12(i)]whileCs
0.15
FA
0.85
PbI
3
could retain about
90% of its initial PCE. Nevertheless, no significant V
OC
change was
observed [Figs. 12(f) and 12(g)], indicating a shallow effect from device
heating from high illumination. The authors found no structural
changes of this material after light soaking in that increased concentra-
tion and hence ascribed photo-bleaching of the perovskite absorber
layer for the fall of the FF and PCE. It is a reversible process, and there-
fore the cell regains its performance if it is stored in the dark for some
time.
85
However, this work did not show solar cell performance recov-
ering after storage in the dark as well. A triple-cation mixed-halide
Cs
0.05
(FA
0.83
MA
0.17
)
0.95
Pb(I
0.83
Br
0.17
)
3
perovskite layer maintained
86% of their initial PCE after 100 h of continuous illumination [Fig.
13(a)]. Applying MAI and FAI surface treatments reduces the surface
interfacial PbI
2
removal and surface iodide defect passivation and thus
allows steady free electron flow.
30
Besides, instead of perovskite solu-
tion incorporation, perovskite used as a single crystal for PSCs leading
to significantly low defect densities and free of grain boundaries gener-
ates high PCEs. 17% PCE reached for MAPbI
3
single crystal-based
PSCs
86
with an active ar ea of 0.09 cm
2
. Whereas the PCE retained
10%toenhancetheactiveareato9cm
2
, it further signifies a signifi-
cant scope to achieve large-area PCE [Fig. 13(b)]. Lv et al. demon-
strated a multilayered encapsulation scheme with a sequential
deposition of compact Al
2
O
3
layer and a hydrophobic 1H,1H,2H,2H-
perfluoro-decyl trichlorosilane layer. Using the protective layers, they
claimed that the PSC devices exhibit excellent water-resistant nature,
losing only 2% of PCE during 5h water immersion
87
[Fig. 13(c)].
The loss of PSC performance under prolonged exposure to higher
TABLE III. Recent advancements in concentrator-based PSC technology.
Method Materials îSolar cell area Stability Reference
Experimental CH
3
NH
3
PbI
3
0.045 cm
2
8% loss of J
SC
after 63 h in 40
suns
71
Experimental FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
23.6% at 14 suns 9.19 mm
2
90% of original îafter 150 h of
exposure under 10 suns
22
Experimental Cs
0.15
FA
0.85
PbI
3
18% between 0.5 and 3 suns 83% of original îwas observed
after 950 h under 13 suns.
72
Experimental CH
3
NH
3
PbI
3
17.8% at 1 sun After 950 h of exposure under
13 suns, 69% of original îwas
retained
72
Theoretical >30% at 100 suns 73
Theoretical Saturates at 26.5%
at 100 suns and above
75
Theoretical CsFAPbIBr 24.93% at 40 suns 81
Experimental (FAPbI
3
)
0.875
(MAPbBr
3
)
0.125
(CsPbI
3
)
0.1
21.6% at 1.78 suns 9 mm
2
19% of original PCE after 5 h
under 1.78 suns
76
Applied Physics Reviews REVIEW scitation.org/journal/are
Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-14
Published under an exclusive license by AIP Publishing
FIG. 12. Overall stability assessment of a PSC device. A schematic illustration of (a) various factors affecting the stability of MAPbI
3
perovskite structure, (b) electronegativity of differ-
ent halide ions, experiencing stronger hydrogen bond between the halide ions and MA/FA ions and strengthening the ionic bond between the halide ions and metal ions, respectively.
(c) Temporal stability of J
SC
of m-TiO
2
/MAPbI
3
/spiro s solar cell under 40 suns light. Inset shows the current–voltage curve recorded at a different times of the exposure.
71
Reprinted
with permission from Law et al., Adv. Mater. 26, 6268 (2014). Copyright 2014 John Wiley and Sons. (d) Degradation of the current-voltage curve of FTO/SnO
2
/FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
/
spiro under long exposure 10 suns illumination.
22
Reprinted with permission from Wang et al., Nat. Energy 3, 855 (2018). Copyright 2018 Springer Nature. (e) Stability of efficiency of
FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
based solar cells under 10 suns.
22
Reprinted with permission from Wang et al., Nat. Energy 3, 855 (2018). Copyright 2018 Springer Nature. Temporal stability of
Voc of M APbI
3
and Cs
0.15
FA
0.85
PbI
3
based solar cells under (f) 1 sun and (g) 13 suns, respectively. Variation of the PCE of the same two perovskite solar cells under 1 sun and 13
suns are shown in (h) and (i) respectively.
72
Reprinted with permission from Troughton et al.,J.Mater.Chem.A6, 21913 (2018). Copyright 2018 Royal Society of Chemistry.
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Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-15
Published under an exclusive license by AIP Publishing
illumination is not entirely due to optoelectronic effects and materials
instability. Illumination induced rise
86
in temperature can impose a
very adverse impact on the device’s mechanical integrity. Previous
reports have emphasized the difference in thermal expansion coeffi-
cients and fracture energy among various layers of a PSC.
88
Baig et al.
placed their PSC based CPV cell under a cooling fan when the illumi-
nation was positioned to 1.78 suns. During the 1st 10min of operation,
the cell lost 5% of the initial PCE. The authors termed this as the
burn-in period. After that, the cell could perform well, and it retained
81% of its initial performance until five more hours. It was observed
that the cell regained 0.75% PCE when it was allowed to rest in the
dark, indication a small effect of photobleaching [Fig. 13(d)].
A theoretical approach to investigate the impact of thermal
stress on the photoluminescence performance of PSCs at higher
illumination complemented these findings by Baig et al.
76
The
authors investigated the changes of different solar cell performance
parameters over a t emperature range of 300–360 K, covering
almost the working environment of an actual solar cell. The V
OC
and PCE exhibited an almost linearly declining nature as the
device temperature went above room temperature and displayed in
Figs. 14(a) and 14(b).Thisispreciselywhatwasexperimentally
reported by Baig et al. [Figs. 13(d) and 13(e)]. However, as shown
in Figs. 14(c) and 14(f),theJ
SC
vs temperature curve’s calculated
nature differed from the experimental observation. The experi-
mental result obtained by this study further exhibits a slowly
decaying character of the J
SC
vs temperature curve. Whereas, even
after considering the positive temperature coefficient of 0.3 meV/K
for their model, the calculated J
SC
vs temperature curve remained
constant with temperature variation [Fig. 14(c)]. PCE always kept
declining with increasing temperature, but the rate of declination
varied with illumination level. The rate of change of PCE with tem-
perature (dPCE=dT) was observed to be higher near 1 sun and 40
sun, and it is lowest near 8 suns. Values of dPCE=dT at different
concentration level (c) is shown in Table IV. The effect of tempera-
ture on the PCE of perovskite cells at higher illumination intensity
was smaller than that of silicon-based cells. The authors simulated
the effect of light concentration and cell temperature on the J
SC,
FF
and V
OC
. The PCE can be calculated using the following equation:
FIG. 13. Recent studies on thermal and moisture stability improvement of a PSC device. (a) Using triple cation-based perovskite and subsequent MAI/FAI salt treatment lead
to enhance the PCE of a PSC device.
30
Reprinted with permission from Hu et al., ACS Appl. Mater. Interfaces 12, 54824–54832 (2020). Copyright 2020 American Chemical
Society. (b) Using a single crystal of MAPbI
3
perovskite, high PCE achieving at different trap densities.
86
Reprinted with permission from Turedi et al., ACS Energy Lett. 6,
631 642 (2021). Copyright 2021 American Chemical Society. (c) J–Vcurves of the encapsulated device (DCL) before and after 5 h of water immersion of MAPbI
3
-based
PSCs with their photograph.
87
Reprinted with permission from Lv et al., ACS Appl. Mater. Interfaces 12, 27277–27285 (2020). Copyright 2020 American Chemical Society. (d)
Stability of efficiency of a (FAPbI
3
)
0.875
(MAPbBr
3
)
0.125
(CsPbI
3
)
0.1
based solar cells under 1.78 suns.
76
Reprinted with permission from Baig et al., Sustainable Energy Fuels 4,
528 (2020). Copyright 2020 The Royal Society of Chemistry.
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Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-16
Published under an exclusive license by AIP Publishing
PCE ¼VOCISC F:(3)
As reported in other experimental reports, FF reduced with
concentration and temperature. Nevertheless, J
SC
remained con-
stant with temperature and increased with concentration.
Whereas V
OC
showed a negative temperature coefficient, the
coefficient was decreased with increasing sample temperature.
These two effects restrain each other to deliver a smaller value
of the negative thermal coefficient of PCE. Interestingly, a
recent work reported that PSC shows better PCE temperature
stability than silicon heterojunction solar cells.
89
The silicon-
based solar cells performed better at low temperatures, while
the PSC could maintain its PCE with minimal temperature
changes.
FIG. 14. Temperature-dependent evolution of (a) V
OC
, (b) PCE and (c) J
SC
at the different solar concentrations (C) of a theoretically modeled CsFAPbIBr based solar cell.
81
Reprinted with permission from Cherif et al., J. Phys. Chem. Solids 135, 109093 (2019). Copyright 2019 Elsevier. (d)–(f) The experimental results of the variation of V
OC
, maxi-
mum power and short circuit current, respectively, for a FA
0.83
Cs
0.17
PbI
2.7
Br
0.3
based solar cells at different temperatures under 1.78 suns.
76
Reprinted with permission from
Baig et al., Sustainable Energy Fuels 4, 528 (2020). Copyright 2020 The Royal Society of Chemistry.
Applied Physics Reviews REVIEW scitation.org/journal/are
Appl. Phys. Rev. 8, 041324 (2021); doi: 10.1063/5.0062671 8, 041324-17
Published under an exclusive license by AIP Publishing
VII. COST ANALYSIS
The idea of using PSCs in CPV is based on their incredibly low
meager manufacturing with ease of synthesis in small sizes suitable for
concentrated light. Even though the efficiency of the single-junction
perovskite solar cell is lower than that of multijunction group III-V
solar cells, PSCs can still take the lead. Unlike other commercial PV
technologies such as silicon or III-V solar cells, PSCs are yet to be pro-
duced by commercial manufacturers. So, the exact manufacturing cost
is not available. Besides, cost analysis depends on some initial assump-
tions like the price of the base materials, instrument usage time, labor
cost, product yield of the particular factory, etc., to name a few. The
cost’s significant contribution is associated with the (organic) HTM
and the (Au or Ag) back electrode part. Besides, transparent conduc-
tive glasses like fluorine-doped tin oxide (FTO) or indium doped tin
oxide (ITO)-based glasses are an effectively cost-effective component
to fabricate a PSC
90
[Fig. 15(a)]. Alternatively, researchers have to
think about the sustainable, low-cost preparation of PSCs. This may
be employing HTL or ETL free layers, low cost transparent conductive
oxide glasses, avoiding glovebox or inert gas chamber processing,
carbon-based solar cells, all layer deposition through solution-
processed techniques, etc. [Fig. 15(b)]. Fabrication strategies and
chemical, compositional alternatives can also en route to develop a
cheaper PSC for their technologically acceptable solution. Moreover,
compromising any factors mentioned above could lead to lesser PCE,
particularly their large-scale adaption. A summarized form of PCE
trend for PSCs ranging from lab cells (0.1 to 1 cm
2
) to mini-modules
(>10 cm
2
) was evaluated
91
as shown in Fig. 15(c). Undoubtedly, most
high-efficiency PSCs to date are fabricated by solution processing
route. However, their stability and prolonged use is still a matter of
concern for the researchers. At this point costing is a crucial parameter
FIG. 15. Comparative cost analysis of a PSC device regarding their material selection, fabrication, installation and maintenance. (a) Price sharing of precursors of each layer of a
conventional PSC.
90
Reprinted with permission from Maniarasu et al., Renewable and Sustainable Energy Rev. 82, 845–857 (2018). Copyright 2017 Elsevier. (b) Schematic repre-
sentation of different ways of cost-effective PSC fabrication strategies. (c) Significant PCE progress in PSCs concerning their different active areas.
91
Reprinted from with permis-
sion from Wilson et al., J. Phys. D: Appl. Phys. 53, 493001 (2020). Copyright 2020 Elsevier. (d) Cost of optical elements with different concentration level.
101
Reprinted with
permission from Paap et al.,J.Phys.Chem.Solids135, 109093 (2019). Copyright 2019 Elsevier. (e) Minimum sustainable price (MSP) of different PV technologies. Change of
MSP for PSCs with module PCE is shown.
92
Reprinted with permission from Song et al., Energy Environ. Sci. 10, 1297 (2017). Copyright 2019 The Royal Society of Chemistry.
TABLE IV. Temperature dependence of PCE at different illumination intensity.
c¼1c¼2c¼3c¼4c¼8c¼15 c ¼25 c ¼40
dPCE=dT 0.041 0.039 0.038 0.037 0.035 0.039 0.035 0.040
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that may affect the trade-off between performance and fabrication.
Thus, analysis of cost per watt of any PV technology varies widely
from country to country, depends on the fabrication strategy and the
survey agency. This review used the cost analysis data mainly from the
reports published by National Renewable Energy Laboratory (NREL),
USA. In the semiconductor industry, manufacturing cost heavily
depends on the product yield.
92
For example, one equivalent sun price
of a triple junction group III–V solar cell (33% PCE) manufacturing
cost can decrease from 100 US $/W to 70 US $/W if the production
capability of the factory is boosted from 50 kW /year to 200 kW/year.
93
Additionally, there are many different PSC device architectures, as
shown in Fig. 2. Therefore, the cost will vary widely depending on the
material and fabrication technology used. For analysis, we are consid-
ering the three most used techniques. The first one is the inexpensive
method of screen printing, spray coating, spin coating, etc. PSCs pre-
pared using this method show PCE of the order of 12% to 15%.
94,95
We name this PSC PSC 1. The second is the noble metal that yields
high-performance PSCs with PCE ranging from 20% to 25%. This
technique uses more sophisticated deposition routes like thermal evap-
oration, vacuum annealing, co-evaporation etc., in addition to spin
coating.
94
This high-quality PSC is named PSC 2. Another PSC fabri-
cated using a mixture of solution processing and magnetron sputtering
deposition technique is named as PSC 3. Table V shows the average
cost per watt of different solar modules, excluding the optical compo-
nents’ cost. Balance of system cost is also kept aside from this calcula-
tion as that would be similar irrespective of the PV technology. As we
see in Table V, PSCs’ minimum sustainable price (MSP) value varies
between 0.21 US $/W to 0.42 US $/W depending on the PCE value
and fabrication techniques used.
92,94
Comparing these values with
the other PV technologies, it is clear that the MSPs of PSCs are
much lower than any of its competitors. While triple junction
III–V solar cells give the best PCE, its MSP is 0.78 US $/W, the
highest among all PV technologies in the list.
96
Commercially
available thin film-based solar cells such as cadmium telluride
(CdTe) and copper indium gallium selenide (CIGS) are also expen-
sive owing to their MSP of 0.55 and 0.67 US $per Watt.
97,98
The
nearest competitor of PSC is crystalline silicon solar cells with an
MSP value of 0.49 US $/W.
99,100
However, silicon-based PV tech-
nology is more or less matured, and its MSP is primarily based on
the commercial ground rather than technological improvements.
99
In this regard, PSCs stand a high chance of further reduction of
MSP once commercial plants take part and the supply chain is
regularized.
Now, the cost of the optical element largely depends on the level
of concentration. As shown in Fig. 15(d), the cost of optical element
varies from USD 0.05/W to USD 0.4/Watt in a logarithmic manner if
the concentration level increases from 1 to 400 suns.
101
III–V solar
cells are primarily used in high concentration CPV systems with a
concentration value of 1000 and above.
96
Aspertheearlierdiscussion,
PSCs are suitable for concentrations level below 100. In this range, the
cost of the optics stays below 0.2 US $/W, which is much cheaper than
the optics for the high concentration of 1000.
Therefore, after adding the cost of the optics with the MSP, PSC-
based CPVs stay still cheaper than their nearest competitor, crystalline
silicon solar cells [Fig. 15(b)], let alone other expensive cells like III-V
solar cells. Even though the efficiency of PSC is nowhere near the
III–V solar cells used in CPV systems, the considerable difference in
cost per watt makes them very eligible for future CPV application. Of
course, stability issues remain to be a challenge for real-world
applications.
VIII. PERSPECTIVE
CPV technology can be more efficient and be more cost-effective
and environmentally friendly than standard flat plate photovoltaics.
This is due to their reduced use of expensive, rare and toxic PV mate-
rial, and PSCs add extra benefit for their incredibly cheap design.
However, being a newly grown technology, PSCs have many areas to
explore before fitting into the commercial CPV systems.
•Differently shaped optics could be tested for conjugate refractive,
reflective optics and their associated benefits. Further investiga-
tions into the cabbage white butterfly wing structure and its con-
tributions to light manipulations can be performed to benefit its
deficient weight. A full 3D simulated model would be beneficial
and synthetic materials utilizing nanocarbon rods and beads to
achieve similar structures and power to weight ratios.
•The reflectance spectra of solar cells and optics used could be
measured at increasing angles of incidence.
•The ultra-high concentrator design prototypes can be built with
different quality optics, and the performance is weighed against
the costs saved.
•One big issue with the CPV system is that it generates consider-
able heat on the solar cell surface. In most HCPV or MCPV,
active cooling must keep the solar cell temperature within the
limit. Most LCPV can work with passive cooling only due to less
heating. However, most hybrid perovskites’ low thermal
TABLE V. Cost analysis of some PV technology.
PV technology
Module
efficiency (%)
Working
concentration level
Minimum sustainable
price (MSP) US $/W References
PSC 1 12 <100 0.25–0.28 94
PSC 2 19 <100 0.21–0.26 94,95
PSC 3 16 <100 0.41 92
Crystalline silicon 19 <100 0.49 99
III–V triple junction 33 1000 0.78 96
CdTe 16 <20 0.55 97 and 102
CIGS 14 <20 0.67 98 and 102
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Published under an exclusive license by AIP Publishing
conductivity creates another hurdle to overcome before being in
real applications.
103,104
A very recent study has some surprising
results that can improve thermal issues. It was observed that the
thinner cell performed better in high luminescence.
105
A perov-
skite solar cell with a 250 nm perovskite layer provided more
PCE in light intensities above 1.5 suns than a 750 nm perovskite
layer. The phenomenon is explained by the reduced bimolecular
recombination rate in a thinner layer. At high illumination, the
charge carrier density becomes high that encouraging bimolecu-
lar recombination. In thin-layer cells, the photo’s transit time
generated carriers to the charge collection layers is lower than the
other cell. This reduces the bimolecular recombination probabil-
ity and increases the PCE. This result also opens up another pos-
sibility on thermal management in perovskite-based CPV. Being
a poor heat conductor, the smaller thickness would help to keep
these very thin cells cool while preserving the photovoltaic per-
formance at the same time.
•Apart from the system’s proper thermal management, the perov-
skite material should possess an acceptable degree of resistance
to thermal degradation. Pure methylammonium lead halide can-
not stand at this point. Cesium doped methylammonium lead
iodides show improved thermal stability.
77,106
Lower dimensional
or mixed dimensional perovskites are also in the pipeline for
improved stability.
107–110
Other approaches like molecular ‘lock-
ing’ or tweaking with the HTL may also be explored for thermal
stability.
111
A very recent article reported that a graphene layer
on top of a silicon solar cell could be a convenient approach to
reduce the solar cell temperature to a great extent while keeping
the photovoltaic performance intact.
112
Similar tactics can also be
adapted for perovskite-based CPV solar cells, owing to these cells’
weak thermal stability. Other alternative approaches like car-
bon
113–115
or inorganic perovskites
116
as the selective carrier
layers improve the stability and simultaneously reduce costs.
•It is already shown that cost per watt of PSC is much lower than
other PV technologies. However, PSCs lack efficiency compared
to other commercial solar cells for CPV systems like III–V solar
cells. All perovskite tandem solar cells can be a workaround here.
Recently, all perovskite tandem solar cells have been reported
with a certified efficiency of 24.2% in a 1 cm
2
cell area.
117
The cell
has also shown good stability of 500 h of operation at 55 to 60 C
under 1 sun in ambient and retained 88% of its initial perfor-
mance. These numbers are quite encouraging to explore all
perovskite tandem solar cells for CPV systems. Zongzi et al. has
estimated the manufacturing cost of an all perovskite tandem
solar cell (PCE 22.1%) to be 0.21 US $/W.
118
This cell has a
Levelized cost of electricity (LCOE) of only 4.22 US cents/kW h,
much cheaper than that of a silicon PERC cell with an LCOE
value of 5.5 US cents/kW h. Therefore, all perovskite tandems
solar cells may stand a good chance in CPV and thus should be
explored.
•Due to their colossal family, hybrid perovskites offer an extended
range of composition and optoelectronic properties. Some of
these perovskites, like MAPbBr
3
, PAPbI
3,
etc., possess wider
bandgap and better stability,
119–121
making them suitable for the
upper layer of a perovskite-silicon tandem solar cells or graded
bandgap device.
122
Silicon/perovskite-based tandem solar cells
have achieved new records in efficiency and stability, and it has
reached near 30% of PCE
123
and excellent stability.
124,125
These
results make the silicon/perovskite tandem solar cells a potential
option for CPV systems. Particularly bifacial silicon/perovskite
tandem solar cells would be interesting to be explored in CPV
systems.
There is an intriguing riddle to understanding how to construct
the system to enhance the light-harvesting capabilities for a sustainable
future. As thermal stability is, however, still one of the major concerns
for PSCs and is primarily responsible for the quick degradation of the
perovskite structures, it originates from a large concentration of vola-
tile MA
þ
components leading to generate PbI
2
. The selection of perov-
skite structure is thus considered a challenging task to produce a
narrow bandgap and anisotropic optoelectronic behavior that could
significantly impact delivering the best solution in terms of high effi-
ciency and excellent stability. Most of the perovskites (either lead or
non-lead based) are struggling with their non-optimal band gaps,
instability, poor charge transport, or they have consisted of non-
abundant elements. Cation mutation and covalency modulation offer
substantial research interest to develop Pb-free, stable ambient cells. It
is crucial that these new technologies show promising developments
and do not represent a risk to society.
IX. SUMMARY
Though hybrid perovskites are yet to be explored sufficiently for
CPV technology in the current scenario, the limited number of theo-
retical and experimental studies to date shows a bright future for this
third generation photovoltaic material in the CPV unit. Most studies
concluded that the PSC could perform well in low concentration sys-
tems with good stability. Contrary to common belief, the PSC showed
good stability up to 370h under 10 suns of concentration and reached
a remarkable 23.6% PCE at 14 suns. All these milestones were
achieved using formamidinium-cesium based hybrid perovskites.
MAPbI
3
, the most popular hybrid perovskite for flat plate PSC, failed
to score well under concentrated light illumination. The restraining
element of the performance is limited due to the instability of the
perovskite absorber, the carrier mobility of the hole transport medium,
and the series resistance of all the electrode layers. A theoretical simu-
lation showed that the appropriate choice of hole transport medium
could boost the efficiency beyond the Shockley–Queisser limit.
Modern silicon or multi-junction-based CPV systems lack market
share because of their high cost compared to flat plate silicon solar
cells. PSCs could be a competitive solution because of their low-cost
manufacturing ability. The current challenge for perovskite CPV solar
cells is improving the device architecture and choosing the appropriate
carrier selective layer to boost performance and stability. There is
enough room for the PSC development for deployment in CPV units
soon.
ACKNOWLEDGMENTS
P.S. acknowledges the DST INSPIRE fellowship (IF160132) for
the financial support through the Ph.D. fellowship. This work has
been conducted as a part of the Newton-Bhaba placement
programme 2019–2020 (Award No. ST/INSPIRE/NBHF/2019/1).
T.M. and S.S. acknowledge the EPSRC (EP/P003605/1) funded
Joint UK-India Clean Energy Centre (JUICE).
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Published under an exclusive license by AIP Publishing
AUTHOR DECLARATIONS
Conflicts of Interest
There is no conflict to declare.
DATA AVAILABILITY
Data sharing is not applicable to this article as no new data were
created or analyzed in this study.
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