Dopant‐Free Ternary Conjugated Polymeric Hole‐Transporting Materials for Efficient Inverted Planar Perovskite Solar Cells

In inverted perovskite solar cells (PSCs), hole transport materials (HTMs) can efficiently improve hole extraction and transfer as well as the crystallization of perovskite films and thus enhance the photovoltaic performance. Herein, two dopant‐free, regular A 1 –D–A 2 –D‐type (D: electron donor; A: electron acceptor) polymeric HTMs, PTPDTBT and PDPPTBT, are developed by integrating the benzothiadiazole unit (A 1 ) with the electron‐accepting species of either a thieno[3,4‐ c ]pyrrole‐4,6‐dione or a pyrrolo[3,4‐ c ]pyrrole‐1,4‐dione segment (A 2 ), respectively, where the thiophene unit (D) results in a kinked molecular geometry. These A 1 –D–A 2 –D‐type terpolymers exhibit comparable nonpolar properties but distinct film‐quality morphology and charge transport characteristics. PDPPTBT with the more insulating side‐chain groups is found to improve the quality of perovskite films cast on top with larger grain sizes and more homogeneous crystallization. As a consequence, the PDPPTBT‐based PSCs without any dopants and additional interlayers display a champion power conversion efficiency of 18.17%, one of the highest values of MAPbI 3 ‐based inverted PSCs using dopant‐free D‐A‐type polymeric HTMs. Furthermore, the PDPPTBT‐based device exhibits negligible hysteresis and high long‐term stability. This work provides a potential strategy to design dopant‐free A 1 –D–A 2 –D‐type polymeric HTMs for efficient and stable PSCs.