How Ammonium Valeric Acid Iodide Additive Can Lead to More Efficient and Stable Carbon-Based Perovskite Solar Cells: Role of Microstructure and Interfaces?

As perovskite photovoltaic devices can now compete with silicon technology in terms of efficiency, many strategies are investigated to improve their stability. In particular, degradation reactions can be hindered by appropriate device encapsulation, device architecture, and perovskite formulation. Mesoporous device architectures with a carbon electrode offer a plausible solution for the future commercialization of perovskite solar cells. They represent a low-cost and stable solution with high potential for large-scale production. Several studies have already demonstrated the potential of the mixed 2D/3D ammonium valeric acid iodide-based MAPbI₃ formulation to increase the lifetime of pure MAPbI₃. They can however not describe the mechanisms responsible for the lifetime improvement. Using a full set of characterization techniques in the initial state and as a function of time during damp-heat aging, new insights into the performance and degradation mechanisms may be observed. With (5-AVA)_0.05MA_0.95PbI₃, the solar cells are very stable up to 3500 h and the degradation of performances essentially results from the loss of electrical contacts mainly located at the interfaces. In contrast, for the neat MAPbI₃, a poor stability is evidenced (T50 = 500 h) and the loss in performance results from the degradation of the bulk perovskite layer itself.