More effective perovskite surface passivation strategy via optimized functional groups enables efficient p-i-n perovskite solar cells

Solution process-based polycrystalline perovskite film has various types of defects. Eliminating these defects is important to increase the performance and stability of perovskite photovoltaics (PePVs). Although materials with various functional groups have been reported, mechanisms for the passivation effect of each molecule are still not well known. In this work, we introduce a piperidine monofunctional group as a defect protection agent and adapt a new bi-functional additive by combining different functional groups such as CN, NH₂, and phenyl under the premise of the defect passivation effect of this mono-molecule. After introducing an additive containing two functional groups, the effect of defect passivation is further enhanced. More interestingly, the optimal device with CN group showed stronger interactions with Pb²⁺, achieving an efficiency of 19.91% with larger grain size of perovskite. Thirty days later, the device also maintained 50% of its original efficiency in air, indicating improved stability. This research demonstrates that a good additive design strategy can help boost solar cell efficiency and stability.