Radical p-Doping Spiro-OMeTAD for Efficient, Stable and Self-Healing Flexible Perovskite Solar Cells.

Spiro-OMeTAD is the primary hole transport material (HTM) for high-efficiency and stable flexible perovskite solar cells (FPSCs). However, the slow oxidation rate and susceptibility to film cracking under stress in Spiro-OMeTAD lead to reduced device stability and efficiency. In this paper, a multi-functional novel self-healing nitroxide radical monomer, 4-[[5-(1,2-dithiolane-3-yl)-1-oxopentyl]amino]-2,2,6,6-tetramethylpiperidin-1-oxyl (DT-TEMPO), has been introduced to address these challenges. DT-TEMPO, on one side, enhances the hole mobility and conductivity by p-doping Spiro-OMeTAD, while boosting the charge transfer process from perovskite to Spiro-OMeTAD with an optimized energy level alignment on the other side. Additionally, DT-TEMPO endows a self-healing capability to Spiro-OMeTAD through the introduction of dynamic breaking and reconstructing disulfide bond. The optimized perovskite solar cells achieve impressive power conversion efficiencies, 25.69% on rigid substrates (certified 25.30%), 21.23% on rigid mini-modules, and 24.19% on flexible substrates. Remarkably, the FPSCs with DT-TEMPO retain over 90% of their initial efficiency even after 20 000 bending cycles (r = 6 mm) and recover to ≈95% of their initial value through the self-healing process.