Polymorphic Phase Control Mechanism of Organic Inorganic Hybrid Perovskite Engineered by Dual-Site Alloying

Abstract

As a next-generation solar cell, perovskite solar cells (PSCs) have been attracting considerable attention. A FAPbI(3) is particularly considered as an optimal material with a proper band gap and thus has been employed as a base material for the PSCs with more than 20% efficiency; however, the competitive polymorphic growth of alpha- and delta-phases is a major hurdle in utilizing this material. To provide the theoretical model of the polymorphic phase competition of FAPbI(3) for the first time, we here investigate how compositional engineering can pave a route to control the polymorphic growth of FAPbI(3) using density functional theory combined with a statistical mechanical treatment of the configurational space. We find that dual-site alloying of both cations and halides is critically important to achieve the specific stabilization of the a-phase while maintaining the good miscibility, thermodynamic stability, and optimal band gap property. Based on our first successful theoretical modeling of the FAPbI(3) system and its polymorphic phase competition behavior during, dual-site alloying, we anticipate deriving new rational guidelines on compositional engineering of organic inorganic hybrid perovskite alloys for designing PSCs with high efficiencies and stabilities.