2D/3D Heterostructure Halide Perovskite Thin Films through an Innovative Spray‐Deposition of Bulky Organic Cation‐Containing Ammonium Salts

Abstract Hybrid halide perovskite involving low‐dimensional (2D or quasi‐2D) perovskites and their three‐dimensional (3D) counterparts provide long‐term stability in solar photovoltaics (PV) applications. Besides stability, perovskite PV commercialization would scalability in roll‐to‐roll fabrication of large‐area devices. Herein, it is reported on a pneumatic spray‐deposition methodology utilized to fabricate 2D/3D heterostructure perovskite films with tunable morphological and optical properties. Ammonium salts featuring bulky organic cations, such as phenethylammonium iodide (PEAI), 2‐thiophenemethylammonium iodide (TMAI), cyclohexylmethylammonium iodide (CMAI), and n ‐dodecylammonium iodide (DDAI) are spray‐deposited on top of 3D‐formamidinium lead triiodide (3D‐FAPbI 3 ) perovskite thin films, to synthesize a series of 2D perovskites, including (PEA) 2 FAPb 2 I 7 , (TMA) 2 PbI 4 , (CMA) 2 FAPb 2 I 7 , and (DDA) 2 FAPb 2 I 7 . X‐ray diffraction (XRD) and grazing incidence wide‐angle X‐ray scattering measurements confirm the evolution of 2D perovskite layer with distinct crystal structure and dimensionality ( n = 1 and 2). Additionally, field‐emission scanning electron microscopy reveals diverse surface morphologies achievable in the 2D perovskite layers. Hyperspectral photoluminescence mapping further demonstrates that the emission at ≈566–570 nm corresponds exclusively to the 2D perovskite phase with n = 2. This study advances the development of 2D/3D heterostructure perovskites using bulky organic cations and underscores the potential of pneumatic spray‐deposition as a scalable fabrication technique for producing next‐generation optoelectronic devices.