NiOx/Spiro Hole Transport Bilayers for Stable Perovskite Solar Cells with Efficiency Exceeding 21%

Hole transport layer (HTL) plays a crucial role in the efficiency and stability of perovskite solar cells (PSCs). The most efficient PSCs based on spiro-OMeTAD (Spiro) generally have stability problems. Here, NiOx/Spiro HTL has been designed and implemented by combining the advantages of these two films. The results indicated that device based on NiOx/Spiro HTL has faster hole extraction ability and better energy alignment than that of pure Spiro device, thus improving the PCE from 19.4% to 21.66%. Compared with the 60% initial efficiency of Spiro-based device, the NiOx/Spiro bilayer devices have higher stability and maintain 90% initial efficiency over 1200 hours. In this work, NiOx is applied to perovskite devices with N-I-P configuration, which provides a possible mitigation strategy to reduce VOC deficit for efficient and stable devices.