Realizing a new class of hybrid organic–inorganic multifunctional perovskite

Abstract

Modification of CH₃NH₃PbI₃ and related hybrid organic–inorganic semiconductors has become an increasingly important effort because of the need to control fundamental material properties. Herein, we closely study material growth to identify the most significant controlling variables determining morphological evolution in a new class of hybrid perovskite alloy. Specifically, drop-casting based perovskite analysis shows that CH₃NH₃Pb(Mn)_yI₃, CH₃NH₃Pb(Fe)_yI₃, CH₃NH₃Pb(Co)_yI₃, and CH₃NH₃Pb(Ni)_yI₃ constitute a unique class of hybrid organic–inorganic perovskite in which growth route most strongly determines morphology. Mn, Fe, Co, and Ni consistently modify CH₃NH₃PbI₃ growth, enabling direct perovskite nucleation to compete with growth through solvent induced intermediate states. We show unambiguously that solvent-perovskite co-crystal formation is responsible for the rod-like thin-film morphology that a great deal of work optimizing perovskite growth in planar heterojunction solar cells endeavors to circumvent. In addition to providing insight into the role of growth route in morphological evolution, we also identity the impact of CH₃NH₃I stoichiometry and the impact of magnetic properties on growth as secondary variables that significantly affect optoelectronic properties. Leveraging this understanding to minimize the impact of morphological phenomena on performance, we closely analyze the compositional impact of these transition metals on optoelectronic quality using CH₃NH₃Pb(Fe)_yI₃ as a model system showing that transition metal inclusion of this type leads to trap-assisted recombination within the perovskite bulk that both sharply limits J_sc and causes significant hysteresis. By comparing device performance of Mn, Fe, Co, and Ni based systems, we show that Mn relieves this sharp limitation on J_sc and almost completely eliminates hysteresis. CH₃NH₃Pb(Mn)_yI₃ thus allows the implementation of direct perovskite nucleation while minimizing the deleterious impact of transition metal inclusion. PL analysis shows that this material is also more emissive than CH₃NH₃PbI₃, making it ideal for light production as well. Methodology and insights developed herein outline a generalizable approach for navigating complexity of perovskite compositional modification.