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

Hole transport layers (HTLs) play 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 a device based on a NiOx/Spiro HTL has faster hole extraction ability and better energy alignment than that of a pure Spiro device, thus improving the PCE from 19.8 to 21.66%. Compared with the 60% initial efficiency of Spiro-based devices, the NiOx/Spiro bilayer devices have higher stability and maintain 90% initial efficiency over 1200 h. In this work, NiOx is applied to perovskite devices with N–I–P configuration, which provides a possible mitigation strategy to reduce the VOC deficit for efficient and stable devices.