Crystallization control of air-processed wide-bandgap perovskite for carbon-based perovskite solar cells with 17.69% efficiency

The preparation of high-efficiency perovskite solar cells (PSCs) in the ambient air environment has been challenging, especially for methylamine-free formamidine (FA)-based PSCs. One of the essential reasons is the slow nucleation rate of perovskite in a high-humidity air environment, leading to the uncontrolled growth of the intermediate phase and poor crystalline quality of the film. Here, we focus on the preparation of wide-bandgap FA-based perovskite films in the ambient air environment. A simple component engineering strategy is proposed to regulate the crystallization process of perovskite film. The nucleation process of perovskite can be significantly promoted by modulating the interaction of components in the precursor solution. The uncontrollable growth of the one-dimensional intermediate phase is suppressed, ultimately resulting in the improvement of the crystallinity of perovskite films. The defect state density of the film is significantly reduced, and the non-radiative recombination processes are effectively suppressed. The efficiency of the hole transport layer (HTL)-free carbon-based PSCs (C-PSCs) reached 17.69 %, which is the highest efficiency of HTL-free C-PSCs prepared with wide-bandgap perovskite (>1.6 eV).