Adjustable Skeleton of Bilateral Lewis Base Passivator for CsPbI3 Perovskite Solar Cells with PCE over 20% and Superior Stability

All-inorganic CsPbI3 perovskite solar cells (PSCs) play a significant role in the new generation photovoltaic technology because of their unique optical band gap and excellent light absorption performance. However, the generation of defect states during the fabrication will cause serious non-radiative recombination and film degradation. Therefore, a new organic additive 4-Thioureidobenzoic acid (4-TBA) was introduced to decrease the defect density and optimize the device performance in this work. Thiourea group and carboxyl group in 4-TBA could not only be anchored on the film surface to passivate uncoordinated Pb2+ defects as bilateral Lewis base, but also form the adjustable skeleton at the grain boundaries to fill Cs+ vacancies, support perovskite framework, boost the charge transfer and enhance the film crystallinity. Owning to the hydrophobicity of benzene ring structure of 4-TBA, the hydrophobic protective layer could be formed on the film surface and grain boundary to isolate the damage of external moisture to the device. Furthermore, with the release of residual stress in the film, the stability of device is substantially improved. Eventually, the 0.02 mol% 4-TBA based device prepared by one-step spin-coating method possesses an ultra-high power conversion efficiency (PCE) of 20.26%, which is one of the greatest efficiencies of all-inorganic CsPbI3 PSC at present. Surprisingly, after 1000 h of environmental stability test, the optimized device still maintains 95.6% of original efficiency without encapsulation, and the PCE attenuation is only 4.4%, showing excellent long-term stability.