Potassium iodide is widely used as an additive to fabricate perovskite solar cells and light-emitting diodes, to enhance their stability and performance. The excess I⁻ from KI fill in the I⁻vacancies and suppress potential pathways for ion migration. The K⁺ cations can bond with undercoordinated halides or passivate negatively charged trap states at the grain surface, which enhances the performance of the device. It can also be used as a catalyst in various reactions such as the synthesis of biodiesel and cyclic carbonates with five-membered rings.