Recent advances in defect passivation of perovskite active layer via additive engineering: a review

The performance and stability of perovskite solar cells (PSCs) are mainly affected by various defects inside the perovskite active layer and the corresponding electron/hole interfaces of transport layers. Much progress has been made in the development of perovskite layer passivation strategies, contributing to the efficient performance of PSCs with improved ambient environment stability. This paper reviews additive engineering techniques for the passivation of the perovskite active layer that have the aim of improving perovskite crystallization, reducing carrier recombination, and improving device stability. Passivation of the active layer by various additives can improve the performance of PSCs by reducing trap states and enhancing moisture stability by reducing the grain boundaries. Optimizing the ratio of PbI₂ in the perovskite precursor has been discovered to be effective in passivating trap states at the grain boundaries and on the surface of the film. Non-radiative recombination trap centers inside the active layer can be passivated through the incorporation of additives such as organic surfactants, elemental iodine, and metal compounds or nanoparticles. This technique has also played a part in improving energy band alignment between the perovskite layer and the respective electron/hole transport layers. The present work covers most of the published reports on the additive engineering approach. Details of precursor preparation, the effects on the properties of the perovskite layer, and the effects on device efficiency, device hysteresis and device stability are presented.