Suppressed Photooxidation in PbSn Perovskite Solar Cells by Field-Modified Selective Contact

Mixed PbSn perovskites are necessary components in all-perovskite tandem and triple-junction solar cells. However, the lifespan of PbSn subcells is severely limited by Sn oxidation. Here, we studied the degradation mechanism of PbSn perovskite devices and discovered that the inefficient extraction of holes from the hole transport layer (HTL) into the conductive electrode results in the hole-induced oxidation of Sn2+ to Sn4+. Such accumulation set the HTL in a higher oxidation state than the redox potential of Sn2+ to Sn4+, leading to a thermodynamically preferred oxidation reaction between the hole and Sn2+.<br/>To address this issue, we aimed to eliminate the HTL while minimizing interface recombination at the newly formed perovskite-electrode contact. Here, we embed high-κ dielectric nanoparticle islands in the perovskite-electrode interface to improve the local electric field, thereby promoting efficient charge extraction from perovskite to the electrode.<br/>We have achieved power conversion efficiencies of 23.7% in PbSn perovskite solar cells, with encapsulated devices retaining 80% of the initial PCE &gt; 1500 hours of maximum power point tracking (MPPT) at room temperature (ISOS-L1) and &gt; 600 hours of operation at 65 °C (ISOS-L2) in a reliability chamber with active heating and temperature monitoring. This is the first time a report of &gt; 20 % of PCE PbSn devices surviving the ISOS-L2 accelerated test over 600 hours.