Efficient flexible perovskite solar cells and modules using a stable SnO₂-nanocrystal isopropanol dispersion

The outstanding advantages of lightweight and flexibility enable flexible perovskite solar cells (PSCs) to have great application potential in mobile energy devices. Due to the low cost, low-temperature processibility, and high electron mobility, SnO2 nanocrystals have been widely employed as the electron transport layer in flexible PSCs. To prepare high-quality SnO2 layers, a monodispersed nanocrystal solution is normally used. However, the SnO2 nanocrystals can easily aggregate, especially after long periods of storage. Herein, we develop a green and cost-effective strategy for the synthesis of high-quality SnO2 nanocrystals at low temperatures by introducing small molecules of glycerol, obtaining a stable and well-dispersed SnO2-nanocrystal isopropanol dispersion successfully. Due to the enhanced dispersity and super wettability of this alcohol-based SnO2-nanocrystal solution, large-area smooth and dense SnO2 films are easily deposited on the plastic conductive substrate. Furthermore, this contributes to effective charge transfer and suppressed non-radiative recombination at the interface between the SnO2 and perovskite layers. As a result, a greatly enhanced power conversion efficiency (PCE) of 21.8% from 19.2% is achieved for small-area flexible PSCs. A large-area 5 cm x 5 cm flexible perovskite solar mini-module with a champion PCE of 16.5% and good stability is also demonstrated via this glycerol-modified SnO2-nanocrystal isopropanol dispersion approach.