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

Nickel oxide (NiO_x) is considered to be an attractive hole transport material in planar inverted perovskite solar cells (PSCs). Unfortunately, the further development of NiO_x-based PSCs is severely restrained due to the poor interface quality between NiO_x 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 NiO_x-based PSCs. Theoretical analysis and experimental results demonstrate that DFCHY plays a role in bridging the NiO_x/perovskite interface, not only suppressing the high oxidation state of Ni³⁺ and enhancing the conductivity in NiO_x 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 NiO_x/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.