Bilayer structure perovskite solar cells with ruddlesden-popper phase for improved stability and performance

Organic-inorganic perovskite solar cells have shown considerable development, and these impressive performance enhancements have generated much interest in their commercial use. The main research challenge in the commercialization of perovskite is its long-term stability. In this study, we aim to improve the stability and performance of the perovskite solar cells by using a bilayer structure of 3D FAPbI₃ (FA = formamidinium) and 2D BA₂PbI₄ (BA = butylammonium) perovskites. The 2D perovskite layer was continuously formed along the surface of the 3D layer via double spin coating, with the 2D layer thicknesses being controlled using various BA₂PbI₄ solution concentrations. Introducing the 2D perovskite effectively suppresses humidity-induced degradation by preventing moisture ingress and reduces recombination loss by passivating surface trap states, thereby considerably improving both the stability and performance of perovskite solar cells. As a result, a bilayer perovskite solar cell with a 55 nm-thick 2D layer maintained ∼93 % of its initial efficiency after 500 h in long-term stability under 85 % relative humidity at 85 °C and exhibited the best efficiency of 20.25 %.