Bifunctional green cellulose derivatives employed for high efficiency and stable perovskite solar cells under ambient environment

•Green cellulose derivatives employed as bifunctional additive for perovskite film.•The perovskite film with large grain sizes and defectless morphology is obtained.•High efficiency (19.53%) of PSCs fabricated under ambient environment is achieved.•The devices (unencapsulated) show well temperature and moisture stability. Organometallic halide perovskite solar cells (PSCs) with high efficiency have attracted enormous attention for commercialization. However, the perovskite undergoes rapid degradation in humid condition, leading to serious decline in both device performance and stability. Herein, an extremely cheap, environmentally friendly and nature cellulose derivative with plentiful hydrogen bonds, cellulose acetate (CA), is introduced into perovskite precursor solution to serve as bifunctional green additive. The hydrogen bonding interactions between the perovskite and CA could passivate the defects at the grain boundaries to suppress the non-radiative recombination, improving the open-circuit voltage and power conversion efficiency (PCE) of PSC. Besides, the long polymer chain of CA can eliminate the annealing-induced lattice tensile/compressive strain during the perovskite film fabrication under ambient environment to enhance its stability. As a result, the dense and defect-less morphology of CA-modified perovskite film with large sized grains, passivated grain boundaries and ideal surface coverage is obtained. The optimized PSC achieves an impressive 19.53% PCE and negligible hysteresis of the photocurrent. Moreover, the thermal stability and humidity resistance of CA-modified PSC are both significantly improved. This strategy provides a promising method for advancing the PSCs application and commercialization.