Crystallization Control for Ambient Printed FA-Based Lead Triiodide Perovskite Solar Cells

Upscalable printing of high-performance and stable perovskite solar cells (PSCs) is highly desired for commercialization. However, the efficiencies of printed PSCs lag behind those of their lab-scale spin-coated counterparts owing to the lack of systematic understanding and control over perovskite crystallization dynamics. Here, the controlled crystallization dynamics achieved using an additive 1-butylpyridine tetrafluoroborate (BPyBF4) for high-quality ambient printed alpha-formamidinium lead triiodide (FAPbI3) perovskite films are reported. Using in situ grazing-incidence wide-angle X-ray scattering and optical diagnostics, the spontaneous formation of alpha-FAPbI3 from precursors during printing without the involvement of delta-FAPbI3 is demonstrated. The addition of BPyBF4 delays the crystallization onset of alpha-FAPbI3, enhances the conversion from sol-gel to perovskite, and reduces stacking defects during printing. Therefore, the altered crystallization results in fewer voids, larger grains, and less trap-induced recombination loss within printed films. The printed PSCs yield high power conversion efficiencies of 23.50% and 21.60% for a 0.09 cm-2area device and a 5 cm x 5 cm-area module, respectively. Improved device stability is further demonstrated, i.e., approximately 94% of the initial efficiency is retained for over 2400 h under ambient conditions without encapsulation. This study provides an effective crystallization control method for the ambient printing manufacture of large-area high-performance PSCs. The crystallization dynamics of alpha-formamidinium lead triiodide (alpha-FAPbI3) perovskites during ambient blade coating are manipulated by employing an additive 1-butylpyridine tetrafluoroborate (BPyBF4), resulting in the highly crystalline perovskite film with large grains, eliminated voids, and reduced defects. This enables the high power conversion efficiencies of 23.50% and 21.60% for a 0.09 cm2 area device and a 5 cm x 5 cm-area module, respectively.image