PTB7 as additive in Anti-solvent to enhance perovskite film surface crystallinity for solar cells with efficiency over 21%.

Anti-solvent washing has been widely used in preparation of compact and uniform perovskite films. However, it often brings more surface defects in the prepared film. Additive PTB7 in anti-solvent is proven to significantly enhance perovskite crystallinity on the film surface. Finally, a champion power-conversion efficiency of 21.41% was achieved in PTB7-washed PSCs which retained over 90% of the initial PCE after 350 h using maximum power point tracking without being encapsulated. [Display omitted] • PTB7 significantly enhance perovskite film surface crystallinity, as evidenced by depth sensitive grazing incidence X-ray diffraction. • PTB7 molecules tend to interact with Pb atoms which slows down crystallization dynamics in the surface region for enhanced perovskite crystallinity and effectively passivates defects at perovskite grain boundary and film surface. • The alkyl chains in PTB7 were shown to improve film surface hydrophobicity. • The champion device obtained an elevated efficiency of 21.41% and improved stability. Low temperature solution-processed organic–inorganic hybrid perovskite films inevitably encounter defects especially on surface and at grain boundaries. Anti-solvent washing has been widely practiced in fabricating uniform and dense perovskite films, but unfortunately it could cause even more defects on surface. Herein, polymer PTB7 was introduced into anti-solvent as an additive to significantly enhance perovskite film surface crystallinity with fewer defects, as evidenced by depth sensitive grazing incidence X-ray diffraction. Such improvements could be attributed to the Lewis base coordination bonds formed between PTB7 and Pb atoms in the surface region which slow down crystallization dynamics for enhanced perovskite surface crystallinity and effectively passivate defects at the perovskite grain boundary and film surface. With PTB7 in anti-solvent, the fabricated perovskite solar cells (PSCs) achieved a champion power conversion efficiency (PCE) of 21.41% from that of 19.79% for the control devices without PTB7. In addition, the hydrophobic alkyl chains in PTB7 were shown to improve film surface hydrophobicity with enhanced environmental stability of both the fabricated films and PSCs. Thus, addition of PTB7 in anti-solvent is proven to effectively improve the performance and stability of PSCs which could be easily applied in the fabrication of PSCs and other perovskite-based optoelectronics. [ABSTRACT FROM AUTHOR]