2D or not 2D? Selectively formed low-dimensional perovskitoids based on chiral organic cation to passivate perovskite solar cells

Abstract

Passivation by low-dimensional (LD) perovskitoid is an effective strategy for reducing defects and stabilizing the bulk 3D perovskite in state-of-the-art perovskite solar cells (PSCs). Here, for the first time, inlaid 1D or 2D perovskite phases from the same organic spacer, chiral β-methylphenethyl ammonium iodide (MPAI), were used to passivate the 3D perovskite film. This is realized via a uniquely temperature-controlled crystal-to-crystal transformation from MPAI containing Ruddlesden-Popper 2D phase to low-D hybrid perovskitoid with the same spacer cation. Upon post-treatment of the bulk 3D perovskite surface with the chiral MPAI, two types of LD perovskitoids could form selectively inside the 3D perovskite film by tuning the annealing temperature and inducing 2D@3D or 1D@3D heterostructures. The formation of two LD chiral perovskitoid phases led to different surface textures, decreased defect-assisted recombination, and brought more favorable energy level alignment. Furthermore, the device characterization turned out that the 2D perovskite is more efficient as a passivator than the 1D perovskitoid due to the better charge transport, less defect state density, and more suitable energy level matching of the 2D@3D film. As a result, the champion PCE of exceeding 22% was achieved with the 2D@3D hetero-perovskite-based devices under standard AM 1.5 G one sun illumination, which after 1300 h-storage in the air ambient (∼30 RH%), remained 98% of the initial performance. This study induced new thinking in controlling the dimensionality of LD perovskitoid, which is also enlightening for other multi-dimensional perovskite-based applications.