Architecting Percolating Ionic Networks in Spiro-OMeTAD via Radical-Dopant Cooperation for Enhanced Hole Transport and Stability

Abstract Doping spiro-OMeTAD has contributed to the power conversion efficiency (PCE) improvement of perovskite solar cells. Nevertheless, the actual roles of the radical and dopant, and their influence on the hole transport, have not been identified much. Herein, we explore the roles of the radical and dopant in doped spiro-OMeTAD and study their effects on hole transport. In particular, we identify the formation of a percolating ionic network (PIN), driven by cooperative radical-dopant interactions, as a previously unrecognized origin of efficient hole transport in doped spiro-OMeTAD. Moreover, we optimized the dopant design by changing the cation bulkiness to maximize hole transport without co-solvents. Finally, we introduce in situ polymerization of the dopant for fixation of the percolated network to improve morphological stability. As a result, we achieve 25.59% PCE with improved stability, retaining over 90% of its initial efficiency after 1600 h under 85 °C and over 95% after 800 h under 60 ± 10% relative humidity.