Toward efficient and stable perovskite photovoltaics with fluorinated phosphonate salt surface passivation

Abstract

Surface passivation has been proven as an effective strategy to improve power conversion efficiency and stability of perovskite solar cells. However, the rationale of choosing appropriate passivator is still not clear yet, whether it should form strong or weak interaction with perovskite beneath. Here, we selectively choose two molecules, fluorinated phosphonic acid and its corresponding phosphonate salt, and monitor the extent of interaction between these passivators and perovskite surface. The effect of these passivation on stability and device performance is also conducted. Higher photoluminescence and carrier lifetime were observed in perovskite film treated with phosphonium salt passivation which possesses stronger interaction with perovskite. The corresponded device shows enhancement in conversion efficiency from 18.27% to 19.44%. Furthermore, water contact angle of passivated perovskite film was exceeding 110.9° as compared to the untreated perovskite (74.5°). This super hydrophobic nature enables excellent long term stability of devices, retaining over 90% of their initial efficiency after 90 days stored under ambient condition with 30% relative humidity.