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

Organo-lead halide perovskite solar cells (PSCs) have attracted tremendous attention owing to their superior photovoltaic properties. However, the device stabilities are still a challenge for the commercialization of PSCs. Spiro-OMeTAD as a widely used hole transport layer (HTL) in PSCs is suffering degradation from the permeate of moisture due to the hygroscopic additive and the presence of pinholes. One approach to diminishing these adverse effects is to insert a buffer layer. Lead sulphide (PbS) is a traditional direct bandgap semiconductor with high hole mobility. We found that when inserting a thin layer of PbS between the metal electrode and spiro-OMeTAD, the PSCs with PbS buffer layer exhibited a better photovoltaic performance and significantly enhanced stability. The superior hole mobility of spiro-OMeTAD/PbS bilayer was considered to be the dominated origin of the device performance improvement. And the hydrophobic nature and dense morphology of PbS enable it to provide an efficient permeation barrier against moisture and metal migration. The champion cell with PbS buffer layer displayed a PCE of 19.58% and maintained almost 100% of its initial PCE after 1000 h stored in ambient air.