Benzodithiophene‐Thienothiadiazole Copolymers as Dopant‐Free Hole‐Transporting Layers Enabling Efficient and Stable Perovskite Solar Cells

The exploration of dopant‐free hole‐transporting materials (HTMs) with excellent optoelectronic properties and defect passivation ability is of great significance for simultaneously improving the efficiency and stability of perovskite solar cells (PSCs). Herein, two donor–acceptor type conjugated polymers PTTDZ‐F and PTTDZ‐Cl with alternating benzodithiophene (BDT) and thienothiadiazole (TTD) units are successfully developed with desirable hole mobilities and conductivities. The formation of non‐covalent interaction (S···N) between thiophene bridge and TTD units significantly improves the co‐planarity of the molecular backbone and promotes the intramolecular charge transfer from BDT to TTD. The hydrophobicity and energy levels of the polymers are finely regulated via introducing different halogen atoms on the BDT moiety. Moreover, the functional groups in polymers efficiently passivate the surface charged traps in perovskite. As a result, champion power conversion efficiencies of 21.50% and 22.20% along with negligible hysteresis have been achieved for devices based on dopant‐free PTTDZ‐F and PTTDZ‐Cl, respectively. The unencapsulated devices also demonstrate excellent long‐term operational stability. Over 93% of their initial efficiencies can be retained after 320 h of maximum output power point tracking under 1 sun illumination. Herein, it paves a new avenue for developing highly stable and efficient HTMs for PSCs.