Surface recrystallized stable 2D-3D graded perovskite solar cells for efficiency beyond 21%

Recently, organic-inorganic hybrid perovskite solar cells (PSCs) have experienced a rapid growth in terms of efficiency. However, the instability of hybrid perovskite materials towards ambient conditions restricts their commercialization. Formation of a thin layer of 2D perovskite over a 3D structure has now boosted the strategy to improve the perovskite stability. This 2D-3D heterostructure enables improved light harvesting properties and enhanced carrier transport of the 3D perovskite along with augmented ambient stability due to the capped 2D layer. Herein, we demonstrate the untapped potential of the surface recrystallized 2D-3D graded perovskite fabricated with the surface treatment of the strategically synthesized multifunctional 4-(aminomethyl)benzoic acid hydrogen bromide (ABHB) molecule. In particular, the bromide ions fill the halide vacancies in the perovskite lattice, while the amine groups and the carboxylic acid functionality significantly minimize the defect states and reduce ion migration. Consequently, ABHB treatment delivers outstanding efficiencies of 21.18% (for a small-area device - 0.12 cm(2)) and 18.81% (for a large-area device - 2 cm(2)) as well as negligible hysteresis. Furthermore, the capped 2D layer restricts moisture penetration into the perovskite layer because of improved hydrophobicity and significantly enhances the ambient stability of PSCs.