Fine coverage and uniform phase distribution in 2D (PEA)2Cs3Pb4I13 solar cells with a record efficiency beyond 15%

Abstract

By introducing phenylethylammonium cation (PEA+) as steric hindrance, the two-dimensional (2D) Ruddlesden-Popper (RP) (PEA)2(Cs)n−1PbnI3n+1 (n ≤ 5) exhibits much stronger phase stability than 3D CsPbI3. However, uncontrollable crystallization process leads to poor coverage and unfavorable phase management in the final (PEA)2(Cs)n−1PbnI3n+1 film, resulting in low power conversion efficiency (PCE < 10%) and poor stability of the related perovskite solar cells (PSCs). Here, we propose an underlying surface engineering (USE) method, which improves the wettability of the substrate and promotes the diffusion of the precursor solution to fabricate a high-quality film with high coverage and low defect density. Further characterizations confirm that this method enables a more uniform phase distribution and achieves an orderly arrangement of small-n and large-n phases from bottom to surface in film, which contributes to effective charge transfer to enhance photocurrent transmission and extraction. As a result, the PCE of (PEA)2Cs3Pb4I13 PSCs was boosted from initial 9.03% to a record value of 15.92%, accompanied by enhanced stability. Encouragingly, this method also has versatility in other RP and Dion-Jacobson (DJ) types of 2D CsPbI3 PSCs, paving a broad road for its commercial application in the future.