Poly(vinylidene fluoride‐co‐hexafluoropropylene) additive in perovskite for stable performance of carbon‐based perovskite solar cells

Abstract

The efficiency of perovskite devices is depending on the crystallization process with a controlled microstructure. Perovskite precursors with polymer additive significantly improve the perovskite film crystallinity, large grain boundaries, serve as passivating defect sites yielding increased power conversion efficiency (PCE). In this study, we improved the hole-transport free carbon-based perovskite solar cells by using polymer additive to passivate the perovskite grains with large size crystal and assist to grow with the preferred orientation of the polycrystalline perovskite layer. The polymer additive systematically alters the morphology of the perovskite films. The perovskite with polymer additives exhibited reduced trap density, which could enhance the open-circuit voltage. The fluoro-polymer as an additive into perovskite layer facilitated a hydrogen bond with organic cation to form H-F bond, which could prevent degradation from moisture. The solar device with 5 wt% PVDF-HFP additives achieved ~14% improvement in open-circuit voltage and yielded a PCE of 11.11%. Moreover, the shelf-life of the solar device retains 86% from its original efficiency with a period of 30 days (stored under ambient condition, 60%-70% humidity). It is revealing that the fluoro-polymer enhances the passivation of perovskite grains and gives a hope in perovskite photovoltaics.