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

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.