PbSe quantum dot passivated via mixed halide perovskite nanocrystals for solar cells with over 9% efficiency

PbSe quantum dots (QDs) have stronger electronic coupling resulting from a large Bohr exciton radius, suggesting PbSe QDs may be able to achieve superior charge separation and transport in optoelectronic devices compared with PbS QDs. However, PbS QDs solar cell have achieved a certified 12.01% power conversion efficiency (PCE), whereas PbSe QD photovoltaics lag behind at 8.2% PCE. One reason for this difference is that there has been significantly less work done on surface passivation of PbSe QDs. Here, the surface passivation of chlorinated PbSe QDs is optimized via a halide ion exchange treatment using mixed halide CsPb(Br/I)₃ perovskite nanocrystals. Champion devices made from treated QDs achieved a PCE of 9.2%, V_oc of 0.56 V, J_sc of 25.7 mA cm⁻², and fill factor of 64%. Average PCEs for optimized cells are 8.9%. Detailed physical characterizations including capacitance‐voltage (C‐V), V_oc, and J_sc as a function of light intensity, transient photovoltage, and photocurrent measurements are all carried out to investigate the mechanism of the improvement in the PCE and to understand the role of the mixed halide perovskites in providing superior surface passivation for PbSe solar cells. At this time, 9.2% is the highest PCE yet reported for PbSe QDs solar cells.