Novel Surface Passivation Technique for Low-Temperature Solution-Processed Perovskite PV Cells.

Low-temperature solution-processed perovskite solar cells are attracting immense interest due to their ease of fabrication and potential for mass production on flexible substrates. However, the unfavorable surface properties of planar substrates often lead to large variations in perovskite crystal size and weak charge extractions at interfaces, resulting in inferior performance. Here, we report the improved performance, reproducibility, and high stability of "p-i-n" planar heterojunction perovskite solar cells. The key fabrication process is the addition of the amine-polymer poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN-P1) to a simple spin-coating process. The PFN-P1 works as a surfactant and helps promote uniform crystallization. As a result, perovskite films with PFN-P1 have a uniform distribution of grain sizes and improved open circuit voltage. Devices with PFN-P1 showed the best efficiency (13.2%), with a small standard deviation (0.40), out of 60 cells. Moreover, ∼90% of the initial efficiency was retained over more than 6 months. Additionally, devices fabricated from PFN-P1 mixed perovskite films showed higher stability under continuous operation at maximum power point over 150 h. Our results show that this approach is simple and effective for improving device performance, reproducibility, and stability by modifying perovskite properties with PFN-P1. Because of the simplicity of the fabrication process and reliable performance increase, this approach marks important progress in low-temperature solution-processed perovskite solar cells.