Optimization of CuIn_1–XGa_XS₂ Nanoparticles and Their Application in the Hole-Transporting Layer of Highly Efficient and Stable Mixed-Halide Perovskite Solar Cells

Abstract

Inorganic hole-transport materials (HTMs) have been frequently applied in perovskite solar cells (PSCs) and are a promising solution to improve the poor stability of PSCs. In this study, we investigate solution-processed copper indium gallium disulfide (CIGS) nanocrystals (NCs) as a dopant-free inorganic HTM in n–i–p type PSCs. Moreover, Cs0.05(MA0.17-FA0.83)0.95Pb­(I0.83Br0.17)3 mixed-halide perovskite with proper crystalline quality and long-time stability was utilized as the light-absorbing layer under ambient conditions. To optimize the cell performance and better charge extraction from the perovskite layer, the Ga concentration in the Cu­(In1–X Ga X )­S2 composition was changed, and the X value was altered between 0.0 and 0.75. It was shown that the CIGS band gap enhances with increasing Ga content; thus, with tunable band gaps and engineering of the energy level alignment, a better collection of photogenerated holes and a reduced electron–hole recombination rate could be achieved. The maximum power conversion efficiency of 15.6% was obtained for the PSC with Cu­(In0.5Ga0.5)­S2 hole-transport layer composition, which is the highest efficiency reported so far for CIGS-based dopant-free PSCs. This value is very close to the efficiency of devices fabricated with doped spiro-OMeTAD as an organic HTM. Additionally, the stability of nonencapsulated PSCs was studied, and CIGS-based devices demonstrated 70% retention after 90 days of aging in the dark and in 50% relative humidity conditions. This result is quite better than the similar measurements for the doped spiro-OMeTAD-based devices.

A brief review of hole transporting materials commonly used in perovskite solar cells

“…[78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][96][97][98][99][100][101][102][103][104][105][106][107][108][109]. In 2017, Ye and co-workers[104] reported a new p-type conductor Cu (thiourea)I [Cu(Tu)I] in inverted PSCs.…”

“…The devices based on it performed a PCE of 19.86% and superior stability (maintaining more than 90% of original PCE for 1000 h after exposure to air with a relative humidity of 80% without any encapsulation). Taghavinia et al fabricated planar n-i-p PSCs employing solution-processed copper indium gallium disulfide (CIGS) nanocrystals as HTM[107]. They studied the influence of Ga concentration on the Cu(In 1-x Ga x )S 2 composition on the device performance.…”

Polyvinylcarbazole as an Efficient Interfacial Modifier for Low‐Cost Perovskite Solar Cells with CuInS2/Carbon Hole‐Collecting Electrode

“…Utilizing this measurement, we can conclude that depositing PMMA and PVK results in decreasing hole transfer resistance (because all other layers and interfaces are the same in the three structures) therefore increasing R ct−1 in the Nyquist plot in case of adding PMMA interfacial layer is related to increasing charge recombination resistance that is a positive effect. The conduction band energy of CuInS 2 is almost the same as the conduction band energy of PSK [ 22 ] (around 4.0 eV); although it is necessary to calculate band bending at the interface of CuInS 2 and PSK layers to conclude what will happen at this interface, electron leakage from PSK to CuInS 2 is likely. PMMA and PVK with E LUMO of −2.0 and −2.2 eV are good blocking layers against electron leakage from the conduction band of PSK to CuInS 2.…”

“…Most of these procedures also require high temperature for calcination or sintering materials, which is higher than the temperature that PSK materials can tolerate. CuSCN [12,21] and CuIn x Ga (1Àx) (S y ,Se (2Ày) ) [22,23] have already been used as HTM on the PSK layer.…”

Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

“…Various inorganic HTMs have also been developed . The ternary or quaternary p‐type inorganic semiconductors already applied in thin film solar cells were reported (e.g., CuInS 2 , CuZnSnS 4 , and Cu 2− x GeS 3 ) . These materials were of interest because of their earth abundance, excellent chemical stability, and environmentally friendly characteristics, as well as good electronic properties.…”