Investigation of the S-Shaped Current-Voltage Curve in High Open-Circuit Voltage Ruddlesden-Popper Perovskite Solar Cells

We report our investigation on the S-shaped current-voltage characteristics in a hot-casting-processed (BA)(2) (MA)(3)Pb4I13 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 (V-oc). The champion device shows a V-oc of 1.21 V and a short current density (J(sc)) of 17.14 mA/cm(2), 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.