Crystallization Control via Alkylammonium Halides for Efficient and Stable Perovskite Solar Cells

Abstract

From fire and agriculture to the industrial revolution, electrical energy has been essential to human civilization. However, global demand has grown unsustainably with the rise of artificial intelligence, while conventional power generation continues to cause pollution and safety issues. To ensure sustain- ability, halide perovskites with superior optoelectronic properties offer great promise for harvesting light, heat, and mechanical energy. This research focuses on interfacial engineering and crystallization control using alkylammonium halides to improve the stability, efficiency, and multifunctionality of de- vices in both conventional (n–i–p) and inverted (p–i–n) perovskite solar cell architectures. 3D perovskite crystallization and surface morphology in alkylammonium chloride (RACl)-doped FAPbI₃ were controlled by tuning the alkyl chain length of RA⁺ to adjust volatility and binding affinity. This approach directed the δ-to-α phase transition, producing high-quality, low-defect film. Further- more, systematic correlation between chain length, volatility, and lattice distortion revealed the molec- ular-level origin of enhanced phase stability and charge transport. Top interface of 3D perovskite layer between perovskite absorbers and hole transport layers (HTLs) were designed using organic cation susceptibility analysis and machine learning–guided screening. By incorporating alkylammonium halides with different electron-donating properties, methoxy-phene- thylammonium iodide (M-PEAI) and cyclohexylammonium bromide (CHABr), strong intermolecular interactions spontaneously formed a thermally stable quasi-2D interlayer, enabling efficient charge ex- traction and surface passivation. Combining targeted molecular structures with Bayesian optimization further identified thermally stable interfacial materials with enhanced charge transport and defect pas- sivation. Buried interface induced by methylammonium chloride (MACl) was further controlled by incorporat- ing a low-solubility chlorine-containing additive to promote heterogeneous nucleation. This approach maximizes the chloride (Cl⁻) effect in the crystallization of perovskite layers during the transition from inorganic ETLs to organic HTLs in inverted PSCs (p–i–n). Additionally, the cooperative role of chloride and cation species was found to regulate interfacial crystallization, resulting in improved morphological uniformity and device reproducibility. This work demonstrates that controlling nucleation, crystallization, and interfacial chemistry is key to advancing stable, reliable, and multifunctional halide perovskite devices for next-generation energy harvesting and optoelectronics.