Enhancing efficiency and stability of perovskite solar cells via a high mobility p-type PbS buffer layer

Although the perovskite solar cells (PSCs) based on organic hole transport materials (HTMs) have demonstrated excellent photovoltaic performance, there are still some obstacles that limiting their future commercialization, one of which is the device stability. Herein, we first report that depositing a (200) orientated PbS thin film upon organic HTMs as buffer layer can significantly enhance the stability and improve the performance of PSCs. The superior hole extraction efficiency of spiro-OMeTAD/PbS bilayer can balance the charge transfer and the hydrophobic nature of PbS could avoid the permeation of moisture. As a result, the PSCs with PbS buffer layer exhibited a better photovoltaic performance (a champion power conversion efficiency of 19.58%) with respect to the reference cells (18.79%), and maintained almost 100% of its initial PCE after 1000 h stored in ambient air. Furthermore, when suffer from some more severe conditions, the device with PbS retained 56% of its initial PCE after 96 h annealing at 85 °C, while only 25% for the reference cells. Our results provide a simple method to avoid the weakness of organic HTMs, and suggest that PbS thin film could be an alternative buffer layer material in PSCs to simultaneously improve the device stability and photovoltaic performance.