Efficient tin-based perovskite solar cells with trans- isomeric fulleropyrrolidine additives

Tin-based perovskite solar cells (TPSCs) are among the best candidates for lead-free photovoltaic technology owing to their low toxicity and high theoretical efficiency. However, the efficiency and stability of TPSCs lag far behind their lead counterparts because of the poor controllability of perovskite film growth and the intrinsically easy oxidation of Sn 2+ . Here we synthesize two pyridyl-substituted fulleropyrrolidines (PPF) with cis (CPPF) and trans (TPPF) configurations and use them as precursor additives. The spatial configurations of the CPPF and TPPF greatly affect their electron density distributions and interactions with perovskite components. Compared with the CPPF, the TPPF has spatially separated pyridine groups that can catch more perovskite colloids through coordination bonds, thus slowing the perovskite crystallization process. The resultant perovskite film displayed better crystal orientation and compactness. The TPPF also remains located at the grain boundaries, improves the interface energy level alignment and suppresses Sn 2+ oxidation. As a result, the TPPF-based TPSCs exhibit a high power conversion efficiency of 15.38% (certified 15.14%) and excellent stability, maintaining 99% and 93% of their initial efficiencies after 3,000 h of storage and 500 h of continuous illumination, respectively. This work highlights the importance of regulating coordination in the precursor solution in preparing high-quality tin-based perovskite films, paving the way to more efficient and stable TPSCs.