Manipulating Electron Density Distribution of Nicotinamide Derivatives Toward Defect Passivation In Perovskite Solar Cells

The design of additives mainly involves selection of functional groups with coordination relationships with defects in perovskite materials. However, it is particularly important to further adjust the geometrical configuration and electronic structure of an additive. Here, the nicotinamide (NA) and its derivative 6-Methylnicotinamide (CNA) with electron-donor functional groups are comparatively analyzed to investigate the effect of molecular dipole and electronic configuration on the defect passivation of perovskite absorbers and the photovoltaic properties of perovskite solar cells (PSCs). Theoretical calculations demonstrate that the CNA molecule with its large molecular dipole combine with the undercoordinated Pb2+ ions in perovskite to form a higher binding energy, which is beneficial to improve the formation energy of Pb-related defects. Experimental characterization confirms that the CNA molecule significantly enhances the coordination effect between acylamino and undercoordinated defective Pb2+ cations, which is conducive to obtain high-quality, low-defect density of state, large grain size, and smooth surface perovskite absorbers. Thanks to the electronic configuration and electronic cloud distribution of CNA molecules, the PSCs yield impressive efficiency as high as 24.33% with excellent environmental storage, heat, and light stabilities. This research provides a research basis for designing additives with steric-charge-dependence to assist perovskite photovoltaics.