Full Defects Passivation Enables 21% Efficiency Perovskite Solar Cells Operating in Air

The lattice defects in the bulk and on the surface of the halide perovskite layer serve as trap sites and recombination centers to annihilate photogenerated carriers, determining the performance and stability of perovskite optoelectronic devices. Herein, the previously reported surface defects passivation engineering is extended to a full defects passivation strategy through stereoscopically introducing the cysteamine hydrochloride (CSA-Cl) in the bulk and on the surface of perovskites. First-principle density functional theory (DFT) calculations are employed to theoretically verify the multiple defects passivation effect of the CAS-Cl on the perovskite. The perovskite layer with full defects passivation exhibits superior carrier dynamics as revealed by femtosecond transient absorption due to the reduced defect density determined by a highly sensitive photothermal deflection spectroscopy technique. Consequently, a high efficiency approaching 21% is achieved for the inverted planar perovskite solar cells (PVSCs). More importantly, the CAS-Cl passivated PVSCs exhibit operation in air, which will be beneficial for the in situ device test for understanding the photophysics involved. This work provides a promising strategy to reduce the defects in both the perovskite bulk and surface for superior optoelectronic properties, facilitating the development of highly efficient and stable PVSCs and other optoelectronic devices.