Replication Data for: Heavy Water Additive in Formamidinium: A Novel Approach to Enhance Perovskite Solar Cell Efficiency

Heavy water or deuterium oxide (D2O) comprises of deuterium, a hydrogen isotope twice the mass of hydrogen. Contrary to the disadvantages of deuterated perovskites, such as shorter recombination lifetimes and lower/invariant efficiencies, we herein divulge the serendipitous effect of D2O as a beneficial solvent additive for enhancing the power conversion efficiency (PCE) of triple-A cation (cesium (Cs)/methylammonium (MA)/formaminidium (FA)) perovskite solar cells from approximately 19.2% (reference) to 20.8% (using 1 vol% D2O) with higher stability. Ultrafast optical spectroscopy confirms trap states passivation increased carrier recombination lifetimes and enhanced charge carrier diffusion lengths in our deuterated samples. Fourier transform infrared spectroscopy and solid-state nuclear magnetic resonance (NMR) spectroscopy validate the N-H2 group as the preferential isotope exchange site. Furthermore, NMR results reveal the induced alteration of the FA to MA ratio due to deuteration causes a widespread alteration to several dynamic processes that influence the photo-physical properties. First-principles density functional theory calculations reveal a decrease in PbI6 phonon frequencies in the deuterated perovskite lattice. This stabilizes the PbI6 structures and weakens the electron-LO phonon (Fröhlich) coupling, yielding higher electron mobility. Importantly, our findings demonstrate that selective isotope exchange potentially opens new opportunities for tuning perovskite optoelectronic properties.