4-Methoxy phenethylammonium halide salts for surface passivation of perovskite films towards efficient and stable solar cells

Surface defects-mediated non-radiative charge recombination in polycrystalline perovskite films has been widely acknowledged to be responsible for the undesired open-circuit voltage (VOC) deficit, which is still a great challenge for perovskite solar cells (PSCs) to achieve the Shockley-Queisser efficiency limit. Herein, we report the use of 4-methoxy phenethylammonium halide salts (4-MeO-PEAX, X = I, Br, Cl) on the surface of formamidinium-cesium (FACs) perovskite films for surface passivation. The impact of halogen species in 4-MeOPEAX on the quality of FACs perovskite films and device performance are comparatively investigated. We find that the prepared FACs perovskite films demonstrate dramatically reduced defect density and surface roughness, improved crystallinity, preferred (001) orientation and prolonged carrier lifetime after the post-treatment by 4MeO-PEACl. Consequently, the 4-MeO-PEACl post-processed p-i-n PSCs have achieved a significantly improved power conversion efficiency of 22.63 % and VOC of 1.13 V. The unencapsulated devices post-treated with 4-MeOPEACl maintained 90 %, 88 % and 84 % of their initial efficiencies, after being thermally stressed at 65 degrees C under dark for 312 h, stored in ambient air for 720 h and operated under continuous 1 sun equivalent illumination with maximum power point tracking at 50 degrees C for 1000 h, respectively.