Cu2ZnGeS4 as a novel hole transport material for carbon-based perovskite solar cells with power conversion efficiency above 18%

Hole transport material (HTM) is vital for further improvement of the power conversion efficiencies (PCEs) of carbon-based perovskite solar cells (C-PSCs). However, up to now the available HTMs for C-PSCs are relatively rare compared with those for Au/Ag based PSCs. In this work, Cu2ZnGeS4 nanocrystals are synthesized and explored as a potential HTM for C-PSCs for the first time. The valence band of Cu2ZnGeS4 is slightly shallower than that of perovskite film, at the same time, the conduction band of Cu2ZnGeS4 is much higher than that of perovskite film, indicating a suitable band alignment between Cu2ZnGeS4 and the perovskite layer. When Cu2ZnGeS4 nanocrystals are employed as HTM for C-PSCs, a maximum PCE of 18.02% is demonstrated. Therefore, our results indicate that Cu2ZnGeS4 nanocrystal is a promising inorganic HTM, which can be optimized to further boost the performances of C-PSCs.