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Achieving Small Temperature Coefficients in Carbon‐Based Perovskite Solar Cells by Enhancing Electron Extraction

Advanced Optical Materials

September 2022
10(23):2201598

DOI:10.1002/adom.202201598

Authors:

Yangyang Zhang

Hebei University of Technology

Wenjin Yu

Peking University

Show all 10 authorsHide

Hole transport layer (HTL)‐free carbon electrode‐based perovskite solar cells (C‐PSCs) have drawn great attention due to their excellent stability and simple fabrication process. However, the photovoltaic parameters of C‐PSCs usually exhibit large negative temperature coefficients (TCs). Herein, the TCs of C‐PSCs can be suppressed by enhancing electron extraction. An efficient electron transport layer (ETL), [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM)‐coated nanoneedle‐like brookite TiO2 (ND‐B‐TiO2) is used as ETL to prepare HTL‐free pure FAPbI3‐based C‐PSCs. Compared with bare ND‐B‐TiO2, PCBM@ND‐B‐TiO2 shows higher electron mobility, and better band alignment with formamidinium lead triiodide (FAPbI3) perovskite, as well as improved contact with perovskite, which leads to enhanced electron extraction and transportation. Consequently, the power conversion efficiency (PCE) of HTL‐free carbon‐based FAPbI3 PSC can reach up to 14.55%, which is one of the highest efficiencies for FAPbI3‐based planar C‐PSCs so far. More importantly, the optimized device is less sensitive to the operating temperature due to the boosted carrier extraction and passivated interface defects, showing a small TC(PCE) of only ≈−0.11%/°C between 25 °C and 85 °C. The work demonstrates that enhancing electron extraction is an effective way to achieve high‐performance C‐PSCs and high‐temperature solar cells.

The SEM images and cross‐section SEM images of the: a) FTO, b) FTO/TiO2‐1.5, c) FTO/TiO2‐3.0, d) FTO/TiO2‐4.5 films. e) TEM and f) HRTEM images of TiO2 (the inset shows a SAED pattern).

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a) Schematic diagram of ETL. AFM measurement of ETLs: b) ND‐B‐TiO2, c) PCBM@ND‐B‐TiO2. d) HAADF STEM image and EDS elemental maps of carbon, titanium and oxygen in the PCBM@ND‐B‐TiO2 components.

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Device performance characterization. The statistic photovoltaic parameters of: a) Voc, b) Jsc, c) FF, and d) PCE of the bare ND‐B‐TiO2 and PCBM@ND‐B‐TiO2 devices from 22 devices for each group. e) The J−V curves of the champion bare ND‐B‐TiO2 and PCBM@ND‐B‐TiO2 devices with reverse scan. f) Stabilized current densities and stabilized power output of the bare ND‐B‐TiO2 and PCBM@ND‐B‐TiO2 devices measured with bias voltages of 0.65 and 0.70 V, respectively.

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Temperature dependence of photovoltaic parameters for control and target devices. Temperature‐dependent J–V curves for the: a) control and b) target samples. Temperature‐dependent: c) Voc, d) Jsc, e) FF, and f) PCE for the control and target samples.

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KPFM images for perovskite film on bare ND‐B‐TiO2: a) under the dark condition, b) under the light condition, and c) CPD. KPFM images for perovskite film on PCBM@ND‐B‐TiO2: d) under the dark condition, e) under light condition, and f) CPD. g) Steady‐state PL spectra. h) TRPL spectra of perovskite films based on the two kinds of ETLs. i) 1/C² versus applied voltage plots (Mott–Schottky).

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Achieving Small Temperature Coecients in Carbon-Based

Perovskite Solar Cells by Enhancing Electron Extraction

Xian Zhang, Yan Guan, Yangyang Zhang, Wenjin Yu, Cuncun Wu,* Jiaheng Han,

Yafei Zhang, Cong Chen, Shijian Zheng,* and Lixin Xiao*

DOI: 10.1002/adom.202201598

1. Introduction

The photovoltaic parameters of solar cells

are generally dependent on the operating

temperature of the device.[1–6] The tem-

perature coecient (TC) describes the

changes of a photovoltaic parameter (X)

with temperature (T). Assuming linear

temperature behavior of over a limited

temperature range, TC(X) is given by:

XXT

()

= (1)

where T0 is 25 °C. The TC is crucial for

the true energy yield calculations of

photovoltaic devices, and the standard

speciﬁcations of commercial photovoltaic

modules usually need to include the TCs

of the device. For the conventional inor-

ganic solar cells, such as silicon, CdTe,

and CuInGaSe, the power conversion e-

ciency (PCE) decreases with increasing

temperature, showing negative PCE TCs of

about −0.44%/°C, −0.28%/°C, −0.32%/°C,

respectively.[7,8] These large PCE TCs are

mainly due to the widened bandgap (Eg)

of the active layer with the increase in temperature. It is worth

noting that although the increase of Eg can slightly reduce the

short-circuit current density (Jsc), the thermal-induced nonradi-

ative recombination at high temperature increases signiﬁcantly.

This leads to a large loss of open-circuit voltage (Voc) and ﬁll

factor (FF) of the device.

For the emerging perovskite solar cells (PSCs), the certi-

ﬁed PCE has reached 25.7%,[9–13] which is comparable to the

eciency of monocrystalline silicon-based solar cells. The sta-

bility of PSCs has been much improved by architecture design

of devices, interface/grain boundary defects passivation, and

inhibition of ion migration.[14,15] Recent results show that its

stability can satisfy the standards of international tests.[16] PSCs

also hold great potential in some speciﬁc scenarios, such as

near space and exoplanet exploration.[17–20] Therefore, lowering

the TCs value of PSCs is not only conducive to improving the

real energy yield of perovskite photovoltaic devices but also con-

ducive to their application in special scenarios.

Previous studies have found that the TCs of perovskite

devices are closely related to the device architecture and the

composition of the active layer.[7,8,21–23] A champion TC(PCE) of

Hole transport layer (HTL)-free carbon electrode-based perovskite solar

cells (C-PSCs) have drawn great attention due to their excellent stability

and simple fabrication process. However, the photovoltaic parameters

of C-PSCs usually exhibit large negative temperature coecients (TCs).

Herein, the TCs of C-PSCs can be suppressed by enhancing electron extrac-

tion. An ecient electron transport layer (ETL), [6,6]-phenyl-C61-butyric acid

methyl ester (PCBM)-coated nanoneedle-like brookite TiO2 (ND-B-TiO2)

is used as ETL to prepare HTL-free pure FAPbI3-based C-PSCs. Compared

with bare ND-B-TiO2, PCBM@ND-B-TiO2 shows higher electron mobility,

and better band alignment with formamidinium lead triiodide (FAPbI3)

perovskite, as well as improved contact with perovskite, which leads to

enhanced electron extraction and transportation. Consequently, the power

conversion eciency (PCE) of HTL-free carbon-based FAPbI3 PSC can reach

up to 14.55%, which is one of the highest eciencies for FAPbI3-based

planar C-PSCs so far. More importantly, the optimized device is less sensi-

tive to the operating temperature due to the boosted carrier extraction and

passivated interface defects, showing a small TC(PCE) of only ≈−0.11%/°C

between 25 °C and 85 °C. The work demonstrates that enhancing electron

extraction is an eective way to achieve high-performance C-PSCs and high-

temperature solar cells.

X. Zhang, Y. Zhang, C. Wu, J. Han, Y. Zhang, C. Chen, S. Zheng

Department of New Energy Materials and Devices

State Key Laboratory of Reliability and Intelligence of Electrical Equipment

School of Materials Science and Engineering

Hebei University of Technology

Tianjin 300130, P. R. China

E-mail: cuncunwu@163.com; sjzheng@hebut.edu.cn

Y. Guan

Department of Chemistry

College of Chemistry and Molecular Engineering

Peking University

Beijing 100871, P. R. China

W. Yu, L. Xiao

State Key Laboratory for Macroscopic Physics and Department of Physics

Peking University

Beijing 100871, P. R. China

E-mail: lxxiao@pku.edu.cn

The ORCID identiﬁcation number(s) for the author(s) of this article

can be found under https://doi.org/10.1002/adom.202201598.

ReseaRch aRticle

Adv. Optical Mater. 2022, 10, 2201598

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