Optimization of CuIn1-xGaxS2 Nanoparticles and Their Application in the Hole-Transporting Layer of Highly Efficient and Stable Mixed-Halide Perovskite Solar Cells

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 (GIGS) nanocrystals (NCs) as a dopant-free inorganic HTM in n-i-p type PSCs. Moreover, Cs-0.05(MA(0.17)-FA(0.83))(0.95)Pb(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-xGax)S-2 composition was changed, and the X value was altered between 0.0 and 0.75. It was shown that the GIGS 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)S-2 hole-transport layer composition, which is the highest efficiency reported so far for GIGS-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 GIGS-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.