Interfacial α-FAPbI3 phase stabilization by reducing oxygen vacancies in SnO2−x

Abstract

•Oxygen vacancies in SnO2−x generate iodine interstitials (Ii) at FAPbI3/SnO2−x interface •Ii modifies FAPbI3/SnO2−x interface by degrading α-FAPbI3 to δ-FAPbI3 and PbI2 •Oxidized black phosphorus quantum dots thoroughly passivate oxygen vacancies in SnO2−x •Organic cation loss was observed at FAPbI3/SnO2−x interface due to oxygen vacancies Reducing nonradiative recombination in SnO2−x has been a critical point for fabricating efficient and stable perovskite solar cells (PSCs). Controlling oxygen vacancies in SnO2−x is an efficient strategy, but most research only presents the consequential results without scrutinizing the phenomenological part of the strategy. Here, we deeply examined and revealed a new beneficial effect of controlling oxygen vacancies in SnO2−x. Oxygen atoms of SnO2−x were responsible for retaining α-FAPbI3 at the FAPbI3/SnO2−x interface by controlling the formation of iodine interstitials, which are strong initiators of unfavorable perovskite phase transitions. Using crystallographic analysis, we observed suppression of these phase transitions when oxygen vacancies were mitigated in SnO2−x by oxidized black phosphorus quantum dots. Furthermore, formamidinium (FA) cation retention was also observed as a beneficial effect of the strategy by introducing hydrogen bonding sources for FA cations at the interface. Our findings suggest the genuine necessity of oxygen vacancy reduction in SnO2−x. Reducing nonradiative recombination in SnO2−x has been a critical point for fabricating efficient and stable perovskite solar cells (PSCs). Controlling oxygen vacancies in SnO2−x is an efficient strategy, but most research only presents the consequential results without scrutinizing the phenomenological part of the strategy. Here, we deeply examined and revealed a new beneficial effect of controlling oxygen vacancies in SnO2−x. Oxygen atoms of SnO2−x were responsible for retaining α-FAPbI3 at the FAPbI3/SnO2−x interface by controlling the formation of iodine interstitials, which are strong initiators of unfavorable perovskite phase transitions. Using crystallographic analysis, we observed suppression of these phase transitions when oxygen vacancies were mitigated in SnO2−x by oxidized black phosphorus quantum dots. Furthermore, formamidinium (FA) cation retention was also observed as a beneficial effect of the strategy by introducing hydrogen bonding sources for FA cations at the interface. Our findings suggest the genuine necessity of oxygen vacancy reduction in SnO2−x.