Recent Advances in Quality Strengthening of Perovskite Films by Additive Engineering for Efficient Solar Cells

In the past decade, perovskite solar cells (PSCs), exhibiting high efficiency, low cost, and flexibility, have made inspiring signs of progress and show great potential in large-scale commercialization as representative third-generation photovoltaic technology. Nevertheless, due to rapid crystallization of perovskite crystals through the solution film-forming technique, a primary challenge is the fabrication of excellent perovskite films with superior optoelectronic characteristics and good flexibility. However, the defects and lattice stresses generated in the perovskite layer during rapid crystallization might diminish the efficiency, robustness, and reliability of PSCs. To date, a variety of techniques are being identified for strengthening the quality of perovskite films, which include interfacial engineering, solvent engineering, doping, and additives engineering. Among these strategies, developing effective additives is of utmost importance in controlling the kinetics of perovskite film crystallization, leading to improved device performance and mechanical stability, especially for flexible PSCs (FPSCs). Herein, the state-of-the-art additives developed in PSCs during the past few years are retrospected, such as ionic liquids, polymers, and small organic molecules, and particular attention is paid to the advanced progress of additive engineering in FPSCs. Moreover, critical perspectives are put forward on the opportunities and challenges of additive engineering in the future development of PSCs.