Enhancing Photostability of Sn-Pb Perovskite Solar Cells by an Alkylammonium Pseudo-Halogen Additive

摘要

High-performance tin-lead perovskite solar cells (PSCs) are needed for allperovskite-tandem solar cells. However, iodide related fast photodegradationseverely limits the operational stability of Sn-Pb perovskites despite the demonstratedhigh efficiency and thermal stability. Herein, this work employs analkylammonium pseudo-halogen additive to enhance the power conversionefficiency (PCE) and photostability of methylammonium (MA)-free, Sn-PbPSCs. Density functional theory (DFT) calculations reveal that the pseudohalogentetrafluoroborate (BF_4?) has strong binding capacity with metal ions(Sn~（2+）/Pb~（2+）) in the Sn-Pb perovskite lattice, which lowers iodine vacancy formation.Upon combining BF_4? with an octylammonium (OA~+) cation, the PCEof the device with a built-in light-scattering layer is boosted to 23.7%, whichrepresents a new record for Sn-Pb PSCs. The improved efficiency benefitsfrom the suppressed defect density. Under continuous 1 sun illumination,the OABF4 embodied PSCs show slower generation of interstitial iodides andiodine, which greatly improves the device photostability under open-circuitcondition. Moreover, the device based on OABF_4 retains 88% of the initialPCE for 1000 h under the maximum-power-point tracking (MPPT) withoutcooling.