Dithiol surface treatment towards improved charge transfer dynamic and reduced lead leakage in lead halide perovskite solar cells

With efficiency surpassing 25%, perovskite solar cells (PSCs) have received much attention because of their excellent potential in photovoltaic field. However, there are some challenging issues still exist which need to be addressed. One issue is that the surface/interface and grain boundaries related defects and traps could work as charge recombination centers during the device operation, compromising the charge transfer as well as the device performance. Another issue is the leakage of toxic Pb, which may cause undesired contamination to water or soil and make devices not appropriate to work outdoors. Herein, the dithiol molecule was introduced to passivate surface defects and traps as well as reduce the Pb leakage. The unsaturated Pb2+ usually acting as recombination centers could coordinate with thiol group to reduce the recombination. Meanwhile, the beneficial band bend was observed, which facilitates the interface charge transfer. Crucially, we confirmed dithiol molecule could help reduce the Pb leakage. Retarded dissolution of PbI2 into water was observed for perovskite films after dithiol treatment, which eventually contributed less Pb leakage. Overall, this study proposes a universal strategy for defects passivation and reduced lead leakage, which is promising for environmental stable optoelectronic applications.