| Summary: | Bismuth triiodide (BiI<sub>3</sub>) is a particularly promising absorber material for inorganic thin-film solar cells due to its merits of nontoxicity and low cost. However, one key factor that limits the efficiency of BiI<sub>3</sub> solar cells is the film morphology, which is strongly correlated with the trap states of the BiI<sub>3</sub> film. Herein, we report a coordination engineering strategy by using Lewis base dimethyl sulfoxide (DMSO) to induce the formation of a stable BiI<sub>3</sub>(DMSO)<sub>2</sub> complex for controlling the morphology of BiI<sub>3</sub> films. Density functional theory calculations further provide a theoretical framework for understanding the interaction of the BiI<sub>3</sub>(DMSO)<sub>2</sub> complex with BiI<sub>3</sub>. The obtained BiI<sub>3</sub>(DMSO)<sub>2</sub> complex could assist the fabrication of highly uniform and pinhole-free films with preferred crystallographic orientation. This high-quality film enables reduced trap densities, a suppressed charge recombination, and improved carrier mobility. In addition, the use of copper(I) thiocyanate (CuSCN) as a hole transport layer improves the charge transport, enabling the realization of solar cells with a record power conversion efficiency of 1.80% and a champion fill factor of 51.5%. Our work deepens the insights into controlling the morphology of BiI<sub>3</sub> thin films through the coordination engineering strategy and paves the way toward further improving the photovoltaic performances of BiI<sub>3</sub> solar cells.
|
|---|