Cage Molecules\nStabilize Lead Halide Perovskite Thin\nFilms

The environmental stability of hybrid organic–inorganic\nperovskite (HOIP) materials needs to increase to enable their widespread\nadoption in thin-film solar and optoelectronic devices. Molecular\nadditives have recently emerged as an effective strategy for regulating\nHOIP crystal growth and passivating defects. However, to date the\nchoice of additives is largely limited to a dozen or so materials\nunder the design philosophy that high crystallinity is a prerequisite\nfor stable HOIP thin films. In this study, we incorporate porous organic\ncages (POCs) as functional additives into perovskite thin films for\nthe first time and investigate the HOIP–POC interaction via\na combined experimental and computational approach. POCs are significantly\nlarger than the small-molecule additives explored for HOIP synthesis\nto date but much smaller than polymeric sealants. Partially amorphized\ncomposites of MAPbI<sub>3</sub> (methylammonium lead iodide, HOIP)\nand RCC3 (an amine POC) form a network-like surface topography and\nlead to an increase in the optical bandgap from 1.60 to 1.63 eV. Further <i>in situ</i> optical imaging suggests that RCC3 can delay the\nMAPbI<sub>3</sub> film degradation onset up to 50× under heat\nand humidity stresses, showing promise for improving reliability in\nHOIP-based solar-cell and light-emitting applications. Furthermore,\nthere is evidence of molecular interactions between RCC3 and MAPbI<sub>3</sub>, as fingerprinted by the suppressed N–H stretching\nmode in MA<sup>+</sup> from Fourier transform infrared (FTIR) spectra\nand density functional theory (DFT) simulations that suggest strong\nhydrogen bonding between MA<sup>+</sup> and RCC3. Given the diversity\nof POCs and HOIPs, our work opens a new avenue to stabilize HOIPs\nvia tailored molecular interactions with functional organic materials.