Multifunctional sodium phytate as buried interface Passivator for high efficiency and stable planar perovskite solar cells

The buried interface defects of SnO₂ electron transport layer (ETL)/perovskite limit the enhancement of photoelectric conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) based on SnO₂. Here, sodium phytate (SP) is employed as a complex molecule for passivating the buried interface defects of SnO₂/perovskite, thus achieving comprehensive improvement of SnO₂ ETL, perovskite film, and interface heterojunction. It is found that the six electron-donating groups (PO₄^2-) in SP can provide multiple chelating sites to bind closely with uncoordinated Sn²⁺ at the buried SnO₂/perovskite interface, thereby enhancing the quality of SnO₂ ETL and passivating the buried interface defects. SP can raise the surface energy of SnO₂ ETL, inhibit perovskite nucleation, and improve the average grain size of perovskite film from 530 nm to 665 nm. Thus, the efficiency of PSC made with SP-SnO₂ is dramatically enhanced from 19.55 % to 22.29 %, which is 14.0 % higher than that of the PSC made with SnO₂ (19.55 %). The unencapsulated devices made with SP-SnO₂ show excellent humidity stability, maintaining 84 % of their initial efficiency after 1000 h in an air environment with a relative humidity (RH) of 60 %, while SnO₂-based PSCs remain only 58 %. The complexation strategy affords a universal method to passivate buried interface defects, revealing broad application prospects in efficient and stable PSCs.