Solvent Engineering for Scalable Fabrication of High-Quality Formamidinium Cesium-Based Perovskite Films Toward Highly Efficient and Stable Solar Modules

Demonstrating the high efficiency and stability of large-area perovskite solar modules (PSMs) is crucial for the industrialization of this innovative photovoltaic technology. However, it remains challenging to achieve the controllable fabrication of high-quality perovskite films over large areas. Herein, a ternary solvent system composed of 2-methoxyethanol (2ME), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP), is thoroughly investigated to fine-tune the solubility, volatility, and coordination characteristics for formamidinium cesium (FACs) perovskite precursor solution. Initially, 2ME and DMF are employed to adjust the volatility and their coordination of Pb²⁺ ions, thereby regulating perovskite nucleation rate. Following this, NMP is introduced as a chelating agent to facilitate the formation of stable intermediate phase, which could extend the processing time window for the solution coating and facilitate crystal growth in the subsequent annealing process. With the optimized solvent system, high-quality, large-area FACs perovskite films are successfully fabricated. The resultant inverted PSMs based on a sole NiO hole-transport layer achieved certified efficiencies of 18.73% and 14.62% with aperture areas of 100.15 and 2123.18 cm². Furthermore, the encapsulated mini-module and sub-module retained 97.2% and 95.8% of their initial efficiencies with maximum power tracking, after aging for 1000 h under 1 and 0.5-sun equivalent white-light illumination, respectively.