Hybrid organic-inorganic perovskites (e.g., CH3NH3PbI3) are promising light absorbers for the third-generation photovoltaics. Herein we demonstrate a modified two-step deposition method to fabricate a uniform CH3NH3PbI3 capping layer with high-coverage and thickness of 300 nm on top of the mesoporous TiO2. The CH3NH3PbI3 layer shows high light-harvesting efficiency and long carrier lifetime over 50 ns. On the basis of the as-prepared film, TiO2/CH3NH3PbI3 heterojunction solar cells achieve a power conversion efficiency of 10.47% with a high open-circuit voltage of 948 mV, the highest recorded to date for hole-transport-material-free (HTM-free) perovskite-based heterojunction cells. The efficiency exceeding 10% shows promising prospects for the HTM-free solar cells based on organic lead halides.

Al-doped ZnO (AZO) modified ZnO nanorods have been applied in CH3NH3PbI3 perovskite solar cells, which can show a positive effect on open circuit voltage and power conversion efficiency. The average power conversion efficiency is improved from 8.5% to 10.07% and the maximum efficiency reaches 10.7%.

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