Introducing moderate iodide vacancies in halide perovskites has been frequently observed to form n-type doping effect and optimize the power conversion efficiency (PCE) of perovskite solar cells (PSCs). However, it has been widely recognized that iodide vacancies are mobile and photochemically detrimental. Herein, tris(2-aminoethyl)amine (TAEA), a branched molecule containing three primary amino groups and one tertiary amino group, is reported to passivate the undercoordinated Pb²⁺ ions and meanwhile n-dope the perovskite surface with its multiple amino groups. After TAEA post-treatment, the PSCs show robustly improved fill factor (FF) from 76.2% to 82.9%, improved open-circuit voltage (V_OC) from 1.08 to 1.16 V, and enhanced PCE from 19.4% to 23.4%. Moreover, the oxygen stability of the TAEA treated perovskite film has been substantially improved simultaneously, which is essentially different from the decreased oxygen stability in the case of using iodide vacancy as the n-dopant. Benefited from the iodide vacancies filling effect by TAEA, the activation energy (E_a) of ions migration in perovskites also increased from 0.43 to 0.67 eV.

Although numerous metal halide perovskite materials have been investigated in the field of optoelectronic, the development of perovskite heterojunctions with exotic structures is still rare. Herein, we report the epitaxial growth of quasi-two-dimensional (Q-2D) perovskites on methylammonium lead iodide (MAPbI₃) single crystals to form perovskite heterojunctions with interfacial bonding. The MAPbI₃ adjacent to epitaxial Q-2D perovskite shows blue shifted photoluminescence with shortened lifetime, which becomes significant with the reduced layer number of the Q-2D perovskites. Our findings suggest the presence of an interfacial strain gradient leading to enhanced photocarrier separation. Accordingly, compared to the MAPbI₃ single crystal detector, the BA₂MAPb₂I₇/MAPbI₃ (BA: n-butylamine) heterojunction-based photodetector demonstrates a bandpass detecting property and exhibits 5 times enhanced external quantum efficiency and 83 times enhanced specific detectivity (D* = 3.26 × 10¹¹ Jones). Remarkably, the unencapsulated BA₂MAPb₂I₇/MAPbI₃ heterojunction is stable in ambient condition for > 300 days. The Q-2D/3D heterojunction shows suppressed ion inter-diffusion due to the presence of Q-2D phase.