Composition engineering of Cu2ZnGexSn1-xS4 nanoparticles hole transport layer for carbon electrode-based perovskite solar cells

Cu2ZnSnS4 (CZTS) and Cu2ZnGeS4 (CZGS) nanoparticles are important inorganic hole transport layers (HTLs) for carbon electrode-based perovskite solar cells (C-PSCs), however the performances of the corresponding C-PSCs are still not satisfactory, which mainly originates from the un-optimized photo-electronic properties of the pristine CZTS and CZGS nanoparticles. Herein, composition engineering via alloying CZTS and CZGS is used to optimize the photo-electronic properties of the resulting CZGxT1-xS HTLs (x = 0, 0.25, 0.50, 0.75, and 1.0), which plays a pivotal role on the performances of the C-PSCs. On one hand, the optimum CZG0.5T0.5S HTL exhibits suitable conduction band energy barrier at the perovskite/CZG0.5T0.5S interface, thus, charge carrier recombination at the perovskite/CZG0.5T0.5S interface could be effectively suppressed. On the other hand, CZG0.5T0.5S HTL exhibit much larger conductivity, which could efficiently transport the holes from perovskite to carbon electrode. Therefore, C-PSCs with the CZG0.5T0.5S HTL could demonstrate a champion power conversion efficiency of 19.76%.