Lone‐Pair‐Induced Lattice Distortion in Lead‐Free Hybrid Perovskites for High‐Performance Nanogenerators
Majid Haji Bagheri, Asif Abdullah Khan, Md Fahim Al Fattah, Mahmoud Almadhoun, Shamaila Shahzadi, Aixi Pan, Md Soyaeb Hasan, Henry Wu, Arash Aghigh, Bhawna Bhawna, François Légaré, Vivek Maheshwari, Dayan BanABSTRACT
Achieving high piezoelectric performance in lead‐free halide perovskites remains challenging because substituting lead typically compromises piezoelectricity through reduced lattice distortion and introduces stability concerns. Here, a lead‐free two‐dimensional Ruddlesden‐Popper hybrid perovskite, (ATHP) 2 SnCl 4 (ATHP = 4‐aminotetrahydropyran), is developed with strongly distorted [SnCl6] 4 − octahedra and enhanced lattice asymmetry relative to its lead‐based analogue. First‐principles calculations reveal pronounced Sn 5s‐Cl 3p hybridization and an anisotropic Sn 2+ lone‐pair lobe, producing stereochemical activity and structural polarization. Cooperative interactions between the lone pair and uniformly oriented [ATHP] + cations stabilize the layered structure, yielding an experimental spontaneous polarization of 8.3 µC.cm −2 , and a d 33 of 65.7 pC.N −1 in the optimized composite. The piezoelectric nanogenerator (PENG) delivers a milliwatt‐level power density of 2.34 mW.cm −2 , among the highest reported for lead‐free hybrid‐perovskite PENGs and competitive with lead‐based systems. The device maintains 65% of its voltage and 25% of its current density at −90°C, corresponding to ∼3.5‐ and ∼12‐fold higher retention than pure poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)), while retaining 76.8% and 71.3%, respectively, at 90% relative humidity. Cryogenic operation is demonstrated by continuously powering an electronic watch for over 15 min at −50°C. These findings establish a lone‐pair‐engineering route to stable, flexible, high‐efficiency lead‐free perovskite PENGs for extreme environments.