Application of ethyl acetoacetate bifocal additive for achieving high-performance perovskite solar cells

Perovskite layer in perovskite solar cells (PSCs) is usually polycrystalline structure with relatively small crystal size, many grain boundaries and a large number of defects, which will be one of the main reasons that limit the improvement of their photovoltaic performance and stability. Hence, improving the film quality and reducing the defect density for perovskite layer are the key to prepare high-performance PSCs. Herein, the ethyl acetoacetate (EAA) containing two functional groups of C--O and -COO is introduced into perovskite precursor solution as a novel bifocal additive, which could not only promote the growth of perovskite, but also effectively deactivate the defect. The results display that EAA can increase the crystallinity and average grain sizes, effectively reduce the defects and significantly restrain the defect-assisted non-radiative recombination, attributing to the strong interaction between EAA and Pb2+ in perovskite. As a result, the perovskite film with EAA shows better film-quality, reduced defects, and suppressed defect-assisted non-radiative recombination. Hence, the EAA device achieves a high PCE of 22.08% with a markedly enhanced open-circuit voltage of 1.15 V. More importantly, the EAA perovskite exhibits excellent humidity stability. The perovskite devices with high water contact angle of 84.4 degrees can retain around 80% of their initial PCEs under 40% RH for 4000 h. The results afford an easy but effective method to high-quality perovskite films with reduced defect density for highly efficient and stable PSCs.