Assisted Solubilization Strategy in Spiro‐OMeTAD for Thermally and Mechanically Stable Perovskite Solar Cells

Abstract The ions migration and de‐doping reactions caused by conventional doping seriously jeopardizes the thermal stability of perovskite solar cells (PVSCs) based on spiro‐OMeTAD as hole transport layer (HTL), which poses a significant challenge for subsequent commercialization. To address these issues, a novel assisted solubilization strategy has been firstly developed using deep eutectic solvent (DES) synthesized from N‐(cyanomethyl)acetamide (NCMA) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). NCMA can form multiple strong interaction modes with LiTFSI through N−H⋅⋅⋅O hydrogen bonding and Li−O/Li−N coordination, which effectively inhibits Li + ions migration at high temperature and increases solubility of LiTFSI in chlorobenzene without acetonitrile and 4‐tert‐butylpyridine (tBP), fundamentally solving de‐doping reaction. In addition, the molecular network with abundant functional groups in DES improves fracture energy of perovskite/spiro‐OMeTAD interface and enhances interfacial adhesion via strong chelation with perovskite and Ag electrode. Consequently, benefiting from tBP removement and inhibited ions migration, the optimized PVSCs achieve a power conversion efficiency (PCE) of 25.02 %, and the unencapsulated device retains over 90 % of initial PCE at 85 °C, 40 % RH for 1200 h (ISOS‐D‐2 standard). This innovative assisted solubilization strategy represents a critical step toward improving device stability and accelerating the commercialization of PVSCs.