Bismuth‐based perovskites are promising candidates for lead‐free and air‐stable photovoltaics. However, the poor surface morphologies and high exciton binding energy of the bismuth‐based perovskites have limited their performances. Herein, the density functional theory calculations unveil that CsBi3I10 possesses favorable optoelectronic properties such as a narrow bandgap, a small effective mass, and relatively high electron mobility. To tackle the poor‐surface morphology problem, the high‐quality CsBi3I10 films are fabricated via gas‐assisted spin‐coating and solvent vapor annealing in ambient conditions. Using the [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) as the electron acceptor, an optimized inverted CsBi3I10/PCBM bulk‐heterojunction structure enables a high power conversion efficiency of 1.18% among the CsBi3I10‐based perovskite solar cells. The approach exemplified in this work could be useful for designing the high‐performance Bi‐based lead‐free perovskite solar cells.

With the increasing energy demands, the production of high-performance perovskite solar cells at economic cost is favorable. However, there are limitations to their commercial applications due to defect formation and instability. Passivation technologies help support their desirable traits. Recently, experiments have proven nanoscale group VA monolayers to be good passivator candidates. Simulated by these recent results, we applied density functional theory to systematically investigate the structural, electronic, optical, and mechanical properties of α and β phases of group VA monolayers, including phosphorene, arsenene, antimonene, and bismuthene in this project. The theoretical results reveal the following: (1) α-phosphorene and β-arsenene have ideal valence band maximum locations, while all monolayers have ideal conduction band minimum locations for enhancing open-circuit potential; (2) most monolayers have light effective masses for improving short-circuit current densities; (3) the location of passivators is important due to their high absorption coefficients; and (4) α-arsenene, α-bismuthene, and α-antimonene are ductile, which can potentially be used in flexible solar cells. Overall, theoretical insights suggest that α-phosphorene and both α- and β-arsenene are promising passivators with the consideration of all the electronic, optical, and mechanical properties.

Halogenated MXenes have been experimentally demonstrated to be promising two-dimensional materials for a wide range of applicability. However, their physicochemical properties are largely unknown at the atomic level. In this study, we applied density functional theory (DFT) to theoretically investigate the halogenation effects on the structural, electronic, and mechanical characteristics of Ti3C2, which is the most studied MXene material. Three atomic configurations with different adsorption sites for four kinds of halogen terminals (fluorine, chlorine, bromine, and iodine) were considered. Our DFT results reveal that the adsorption site of terminals has a considerable impact on the properties of MXene. This can be ascribed to the different coordination environments of the surface Ti atoms, which change d-orbital splitting configurations of surface Ti atoms and the stabilities of systems. According to the density of states, crystal orbital Hamilton population, and charge analyses, all the considered halogenated MXenes are metallic. The electronic and mechanical properties of the halogenated MXenes are strongly dependent on the electronegativity of the halogen terminal group. The Ti-F bond has more ionic characteristics, which causes Ti3C2F2 mechanically behave in a more ductile manner. Our DFT results, therefore, suggest that the physicochemical properties of MXenes can be tuned for practical applications by selecting specific halogen terminal groups.