Phenol is introduced as a solvent additive in the perovskite precursor solution. In a wide concentration range between 5 and 75 mg ml−1, it can improve the quality of active layers by decreasing the concentration of defect states, leading to a 20% enhancement in perovskite solar cell performance. O–Pb coordination and complete removal of the additive contribute to the high quality of the perovskite film.
