Highly Stable and Efficient Formamidinium-Based 2D Ruddlesden-Popper Perovskite Solar Cell via Lattice Manipulation.

Formamidinium-based (FA) 2D perovskites have emerged as highly promising candidates in solar cells. However, the insertion of 2D spacer cations into the perovskite lattice concomitantly introduces micro-strain and unfavorable orientations that hinder efficiency and stability. In this study, by finely tuning the FA-based 2D perovskite lattice through spacer cation engineering, we achieved a stable lattice structure with balanced distortion, micro-strain relaxation, and reduced carrier-lattice interactions. These advancements effectively stabilize the inherently soft lattice against light and thermal aging stress, particularly extreme temperature changes. To reduce the photocurrent loss induced by undesired crystal texture, we further employed a polarity-matched molecular-type selenourea (SENA) additive to modulate the crystallization kinetics. The introduction of the SENA significantly inhibits the disordered crystallization induced by spacer cations and drives the templated growth of the quantum well structure with a vertical orientation. This controlled crystallization process effectively reduces crystal defects and enhances charge separation. Ultimately, the optimized FA-based perovskite photovoltaic devices achieved a remarkable power conversion efficiency (PCE) of 20.03% (certified steady-state efficiency of 19.30%), setting a new record for low-n 2D perovskite solar cells. Furthermore, the devices exhibited less than 1% efficiency degradation after operating at maximum power point for 1000 hours and maintained 92.3% and 91.1% of the initial efficiency after aging at 85°C for 720 hours and 50 cycles of cold-warm shock, respectively. This article is protected by copyright. All rights reserved.