Spatially Isomeric Fulleropyrrolidines Enable Controlled Stacking of Perovskite Colloids for High-Performance Tin-Based Perovskite Solar Cells.

The advancement of tin-based perovskite solar cells (TPSCs) has been severely hindered by the poor controllability of perovskite crystal growth and the energy level mismatch between the perovskite and fullerene-based electron transport layer (ETL). Here, we synthesized three cis-configured pyridyl-substituted fulleropyrrolidines (PPF), specifically 2-pyridyl (PPF2), 3-pyridyl (PPF3), and 4-pyridyl (PPF4), and utilized them as precursor additives to regulate the crystallization kinetics during film formation. The spatial distance between the two pyridine groups in PPF2, PPF3, and PPF4 increases sequentially, enabling PPF4 to interact with more perovskite colloidal particles. These interactions effectively enlarge the precursor colloid size and decelerate the crystallization rate of the perovskite, resulting in high-quality PPF4-based perovskite films with reduced defect density and lower exciton binding energy. Additionally, we incorporated a well-defined fullerene bis-adduct, C60BB, as an interlayer between the perovskite and PCBM layers to optimize energy level alignment. Through the synergistic effects of PPF4 and C60BB, our champion device achieved an efficiency of 16.05% (certified: 15.86%), surpassing the 16% efficiency bottleneck and setting a new benchmark for TPSCs. Moreover, the devices exhibited outstanding stability, retaining 99% of their initial efficiency after 600 hours of maximum power point tracking under 1 sun condition.