Improved Efficiency and Stability of Perovskite Solar Cells Using a Difluorobenzothiadiazole-Based Interfacial Material

The humidity stability of the perovskite solar cell (PSC) is an important issue, which limits its commercialization and practical application. To construct a waterproof interface upon a perovskite film is a valid strategy to improve the stability. In this article, a difluorobenzothiadiazole-based polymer, PffBT4T-C9C13, is employed as an interfacial material and a water barrier on the perovskite by a well-designed deposition method. A uniform perovskite film with a large crystal grain is obtained after the decoration of the polymer owing to its positive impact on the crystal growth. PffBT4T-C9C13 not only protects perovskite from water corrosion but also passivates the surface defects of perovskite. Charge accumulation at the interface is sufficiently suppressed, which is of benefit for the charge transport and extraction. As a result, PSCs with the structure of ITO/TiO2/MA1–xFAxPbI3/PffBT4T-C9C13/spiro-MeOTAD/Ag achieve the highest power conversion efficiency of 20.21%. More importantly, remarkable improvement of the humidity stability is achieved for both perovskite films and PSCs with PffBT4T-C9C13. The unencapsulated device retains more than 80% of its highest power conversion efficiency after 14 days’ aging in humidity of about 50%, and no apparent decomposition of the modified film is observed in 93 days. Therefore, this scheme provides a valuable approach to develop highly efficient and highly stable PSCs.