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(a) Picture showing the synthesis of N-doped 3D graphene foam and transfer it for DSSC CE; (b) and (c) schematic illustrating the assembly of DSSC using N-doped 3D graphene foam and triiodide reduction process at the CE. Reprinted with permission from John Wiley and Sons. 104
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To date graphene and graphene-derived materials have created an immense research interests due to its extraordinary physical, chemical, and physiochemical properties, which delineated graphene as an outstanding material for future electronics, optics, and energy-harvesting devices. Typically, graphene has high mobility and optical transparency alon...
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... (Pt) is widely used as CEs for DSSCs owing to its excellent catalytic activity and low resistance. However, due to high cost, low abundance, and low chemical inertness, replacing Pt with other materials is becoming a fundamental issue for DSSCs. So far, it has been reported that different forms of carbon materials are quite stable and best alternatives for Pt CEs in DSSCs. 97 In this context, graphene has several advantages for being a potential CE material for solar cells: high electrical con- ductance, high thermal conductivity, ultrahigh transmittance, and excellent mechanical properties. In particular, graphene exhibited remarkable transparency in the entire solar spectrum including IR region. Therefore, graphene CEs are quite advantageous for those types of solar cells/tandem solar cells, which need to absorb the entire range of photon energies (from UV-visible to IR) to generate excitons ef fi ciently. 21,33,98,99 Furthermore, the high surface area of a 2D graphene sheet (2630 m 2 /g), in addition to its intrinsic high transmittance and charge mobility, offers greater versatility as a CE in DSSCs. Hasin et al. 9 fi rst reported the triiodide reduction capability of graphene and, thus, demonstrated the wide pos- sibilities for applications in DSSC CEs. The report also showed that the surface functionalization by cationic polymer is one of the promising ways to increase the electrocatalytic property of graphene fi lms, which has numerous advantages over improving DSSC ef fi ciency. Kavan et al. 100 demonstrated the graphene nanoplatelet- based DSSC CE as an optically transparent cathode, which is electrocatalytically active for the I À 3 /I À redox reaction. They fabricated the graphene-based cathode using a drop-cast method, and the device showed a PCE of about 5%. Roy-Mayhew et al. demonstrated the functionalized graphene sheet as DSSC CE with a PCE of 3.83%. They demonstrated the enhancement of electrocatalytic activity of graphene by functionalizing it using poly(ethylene-oxide)-poly(propylene-oxide)- poly(ethylene-oxide) triblock copolymer. In this context, Das et al. 31 showed the functionalization of large-scale CVD graphene using fl uorine (F À ions) ions with higher catalytic activity toward triiodide reduction compared to pristine graphene. The PCE of the DSSC showed ; 2.56% with corresponding V OC , J SC , and FF of 0.66 mV, 10.9 mA/cm 2 , and 35.9% respectively [Figs. 7(j) – 7(n)]. 31 Similarly, HNO 3 -doped graphene showed an enhancement in the electrocatalytic activities of graphene with a DSSC ef fi ciency of ; 3.21% as shown in Figs. 7(f) – 7(i). The cell performance is lower than that expected, and this is due to the lower FF, which causes potential voltage drop at the graphene/FTO interface. Therefore, it has been well demonstrated that functionalized graphene is more effective than pristine graphene to enhance the kinetics of I À 3 reduction at cathode. As described in Ref. 54, graphene ’ s electrocatalytic activity strongly varies with its defect concentration and oxygen-containing functional groups as shown in Fig. 8. Similarly, electro-catalytic activities of graphene are also associated with its active sites, which play a key role in CT at the interface. Few reports showed that the attachment of other functional groups such as – COOH, – CO, – NHCO – in graphene effectively improves graphene ’ s electronic as well as electrocatalytic properties. 102,103 Recently, Xue et al. proposed a new graphene-based 3D architecture for DSSC CEs as illustrated in Fig. 9. In this report, 3D graphene oxide foam is doped with nitrogen and used as a CE of DSSC, which showed a PCE of 7.07%. Likewise, graphene embedded with polymer materials also showed promises for electrocatalytic cathode for DSSC. Several conducting polymers like, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), polyaniline (PANI) have been used to enhance the electrocatalytic activities as well as the con- ductivity of the graphene/polymer composite. Hong et al. reported the PEDOT:PSS/graphene composite CE for DSSCs with 4.5% PCE. In this work, they demonstrated the increment of J SC of DSSC after addition of a small amount of graphene in PEDOT-PSS, which was attributed to the higher catalyzing ability of graphene for iodine reduction at the CE. 105 Similarly, the graphene/PEDOT composite fl exible electrode was demonstrated by Lee et al. 106 In their report, they fabricated the graphene/PEDOT CE on the fl exible PET substrate and assembled as DSSC. The PCE of DSSC without TCO and Pt is 6.26%, which is almost comparable to DSSC with TCO and Pt ( ; 6.68%). 106 Similarly, MnO 2 -PANI/r-GO composite showed a PCE of ; 6.15% with V OC , J SC , and FF of about 0.74 mV, 12.88 mA/cm 2 , and 65% respectively. One recent approach showed that the polydiallyldimethylammonium chloride/graphene oxide (PDDA/graphene) composite was used as DSSC CE with ; 9.5% PCE. In this report, Xu et al. fabricated the cationic polymer (PDDA) decorated on neg- atively charged graphene oxide (GO) by the layer-by-layer assembly method and found enhanced catalytic activity of GO due to the charge disparity between the electronegative carbon atoms and the nitrogen of ammonium ions. On the other hand graphene/NP composite electrodes stipulate the research based on composite cathode toward high-ef fi ciency DSSC. In this course of research, NPs anchored with graphene has also been demonstrated as a composite CE for DSSCs. Pt NP-anchored graphene was demonstrated for enhancing graphene ’ s electrocatalytic activity for triiodide reduction in DSSCs. 63,107,108 The goal of these studies was to reduce Pt loading in DSSC CE by incorporating Pt/graphene composite electrodes without affecting its PCE. In this context, one report was found based on graphene/Ag NW composite electrodes with a PCE of 1.61%. 109 Nonmetallic NPs such as CoS, NiO, Ni P , and TiN have been used to fabricate graphene- based composite electrodes. CVD graphene/CoS composite electrodes showed a PCE of 3.42% with V OC , J SC , and FF of ; 0.72 V, ; 13.0 mA/cm 2 , and 36.40%, respectively. 101 Das et al. 101 demonstrated that implantation of CoS NPs on graphene enhanced catalytic activities of the composite electrodes due to the formation of catalytically active triple junction sites, which further facilitates the CT reactions at the DSSC cathode [Figs. 7(a) – 7(e)]. Similarly, Wen et al. 112 showed the graphene/TiN NP composite electrodes for effective DSSC cathode with a PCE up to 5.78%. On the other hand, graphene/CNTs also showed high promises as catalytic electrodes for triiodide reduction in DSSCs, hence, demonstrated in recent reports. 113 – 115 Table I lists the details about the performances of DSSCs based on graphene and graphene-derived CE. Apart from DSSCs, semiconductor quantum dots (QDs) as light absorbing materials in QD-sensitized solar cells (QDSSC) also awake great interest by their fascinating features. In view of tuning the absorption spectrum of semiconductor QDs, 126 probing the particle size is an ef fi cient way to harvest the entire range of the solar spectrum. 127 In addition, owing to the unique electronic band structure, QDs can overcome the Shockley – Queisser limit of energy conversion ef fi ciency. 128 The ability of QDs to harvest hot electrons and to generate multiple carriers makes them a viable candidate for light-harvesting sensitizers in solar cells. 129 Several semiconductor materials (CdS, CdSe, PbS, etc.) 130 – 135 have been used as light sensitizers on wide band gap mesoporous metal oxide layers (TiO 2 and ZnO) due to their low cost and simple sensiti- zation processing. The device function of QDSCs is analogous to DSSCs [Fig. 10(a)], where the dye molecules are replaced with semiconductor QDs. Besides, the theoretical ef fi ciency of QDSCs is as high as 44%, the practical performance still lags behind that of DSSCs at present. 139 Hodes 136 exclusively compared the critical factors of QDSCs to answer the question, why it is inferior to DSSCs. The main issues in QDSCs are (i) fast electron recombination at surface states of the TiO 2 /QD junction ascribed to a slower electron injection rate from QDs to TiO 2 [Fig. 10(b)] and (ii) hole trapping between QDs. To achieve competitive photoconversion ef fi ciency with DSSCs, the above factors have to be bottlenecked in QDSCs. In the context of promoting QDSC performance, different approaches were demonstrated — doping anode, 140,141 shell layer, 142 QD ...
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... Graphene and ITO are mostly used in solar cell applications due to their excellent optical and electrical characteristics [16][17][18]. This may be because of the absorption of light, which many researchers utilize in the coating to enhance the transparency of metal oxide materials. ...
In this work, we synthesized graphene (g)-incorporated Indium Tin Oxide (ITO) and investigated its structural, morphological, electrical, optical and magnetic properties. The ITO materials, including the 1 % and 2 % g-ITO variants, have a cubic crystal phase, while graphene possesses a hexagonal lattice structure. The Raman spectra exhibited distinct ITO peaks, along with the presence of active modes such as A 1 , E 1 , and E g associated with the CC stretching peak. UV-DRS was performed to study the optical absorption properties in the range of 200-900 nm for the as-prepared ITO, ITO-g (1 %), and ITO-g (2 %) composites. The composite exhibited energy absorption at wavelengths of 320, 314, and 312 nm for ITO, ITO-g (1 %), and ITO-g (2 %), respectively. The photoluminescence spectra exhibited a prominent ultraviolet emission peak at a wavelength of 374 nm as well as a blue-green emission peak at 446 nm, which were found in both the pure and doped samples. Finally, electrical and magnetization was conducted on both unadulterated and g-ITO.
... These distinct characteristics make graphene-based materials appropriate for an extensive range of applications. For instance, graphene is utilized in a variety of thermal, optical, and electrical systems, such as temperature sensors [8,9], transparent electrodes [10], conductive composites (electrically, thermally, or both) [11][12][13], solar cells [14], and thermal imaging [15]. ...
... In this work, we tested liquid phase exfoliated (LPE) graphene material as an HTL [66], taking advantage of the high electrical conductivity and stability of graphene [67]. Further-more, liquid phase exfoliation of graphite is a promising method for producing a graphene dispersion that is simultaneously scalable, water-based, and that can be performed at room temperature, offering a high yield [68] compared to GO or rGO. ...
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... Owing to these properties it has been widely used in optoelectronic applications such as transparent conducting electrodes [8], graphene-based perovskite solar cells (power conversion e ciency ~ 20.3%) [9,10], photodetectors [11], FETs [12]. Many researchers have synthesized monolayer graphene for several applications in the elds like composite materials, energy harvesting and storage, electronics/bioelectronics, photonics, and biological methods [13,14]. ...
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Dye‐Sensitized Solar Cells (DSSCs), also known as Grätzel cells, are a third‐generation photovoltaic technology that has garnered extensive interest due to its simplicity of fabrication, economical, and relatively high power conversion efficiency (PCE). The PCE of the photovoltaic cells is primarily related to the architecture of the cells, as well as the electrodes and electrolyte employed. Using zinc oxide (ZnO) coupled with two‐dimensional graphene as photoelectrode enables efficient charge transfer and minimizes electron–hole recombination in the DSSCs, resulting in improved performance. This review outlines the feasibility and performance enhancement of ZnO/graphene nanocomposite and its derivatives as photoelectrode for DSSCs. The structural features, optical properties, electron transport, and dye interaction of the ZnO/graphene nanocomposite‐based photoelectrode were considered in this review. In addition, the limitations of ZnO/graphene derivatives as photoelectrodes and their solutions were extensively discussed, as well as their prospects. The ZnO/graphene‐based photovoltaic cells exhibit an efficiency of up to 11.5% under different dyes and electrolytes. The recent progress achieved with this photoelectrode, which is a viable substitute for titanium dioxide (TiO2), is also thoroughly reviewed. Highlighted the structural, optical, electron transport, limitations, and interaction of dye in ZnO/graphene derivatives for DSSCs. ZnO/graphene‐based DSSCs would be very helpful for researchers studying these materials as photoanode in DSSCs. A detailed electron transport mechanism of ZnO/graphene‐based DSSCs have been intensively reviewed.
