Enhancing Spectral Response of Thermally Stable Printed Dion–Jacobson 2D FAPbI₃ Photovoltaics via Manipulating Charge Transfer

Two-dimensional (2D) perovskites are structurally more stable than their three-dimensional (3D) analogs. However, the overwhelming majority of 2D perovskite solar cells (PSCs) incorporate volatile methylammonium (MA) cations, which unfortunately compromise their efficiency and stability. Here, we report efficient and thermally stable single-cation-formamidinium (FA) Dion–Jacobson (DJ) PSCs by manipulating charge transfer. Introducing a small amount of thiourea (TU) to the precursor yields printed 2D perovskite films with uniformly distributed multiple phases in comparison to gradient phase distribution in the control film. Consequently, markedly enhanced spectral response and charge extraction are realized in TU-based devices, primarily owing to the efficient charge transfer from small- n to large- n phases. Eventually, the champion DJ-type FAPbI 3 ((BDA)(FA) 4 Pb 5 I 16 ) PSCs exhibit a high short-circuit current density of 20.48 mA cm –2 and an efficiency of 17.27%, setting an efficiency record for printed DJ-type PSCs ( n ≤ 5), and demonstrate better thermal and operational stability than their DJ-MAPbI 3 counterparts.