| Summary: | We report our investigation on the S-shaped current–voltage characteristics in a hot-casting–processed (BA)2 (MA)3Pb4I13 Ruddlesden–Popper (RP) perovskite solar cell. The two-dimensional perovskite solar cells are fabricated with NiOx as the hole transport layer (HTL), which leads to significantly high open-circuit voltage (Voc). The champion device shows a Voc of 1.21 V and a short current density (Jsc) of 17.14 mA/cm2, leading to an overall power conversion efficiency (PCE) of 13.7%. Although the PCE is much higher than the control device fabricated on PEDOT:PSS, a significant S-shaped current–voltage behavior is observed in these NiOx-based devices. It is found that the S-shaped current–voltage behavior is related to the lower dimensional phase distribution and crystallinity at the bottom interface of the RP perovskite layer, and the S-shaped distortion is less severe after the device ageing test.
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