A buried interface modification strategy for enhancing the photovoltaic performance of NiOx-based inverted perovskite solar cells

Nickel oxide (NiOx) is considered to be an attractive hole transport material in planar inverted perovskite solar cells (PSCs). Unfortunately, the further development of NiOx-based PSCs is severely restrained due to the poor interface quality between NiOx and perovskite layers. In this paper, a buried interface modification strategy using a polar molecule material 4,4-difluorocyclohexylamine hydrochloride (simplified as DFCHY) is introduced to improve the performance of NiOx-based PSCs. Theoretical analysis and experimental results demonstrate that DFCHY plays a role in bridging the NiOx/perovskite interface, not only suppressing the high oxidation state of Ni3+ and enhancing the conductivity in NiOx film, but also passivating buried interface of perovskite film and improving its crystallinity, further effectively reducing trap density and enhancing charge transfer at the interface of NiOx/perovskite layers. The champion inverted PSCs using DFCHY as a buried interface modifier achieve a power conversion efficiency of 17.08% with negligible hysteresis. Furthermore, the unencapsulated PSCs with DFCHY modification exhibit outstanding long-term stability, maintaining above 90% of their initial efficiency after 1000 h storage in a nitrogen-filled glovebox.