Thienoisoindigo-Based Dopant-Free Hole Transporting Material for Efficient p–i–n Perovskite Solar Cells with the Grain Size in Micrometer Scale

In this study, a series of 2,2′ and 3,3′ substituted thienoisoindigo (TII)-based small molecules (H3–H7) were synthesized by using 1,3-di(9H-carbazol-9-yl) benzene, N-phenylcarbazole, triphenylamine, and benzene as electron donor (D) at the periphery, while TII as electron acceptor (A) at the core. The highest occupied molecular orbital energy levels of H3–H7 range from −5.31 to −5.43 eV, while their lowest unoccupied molecular orbital energy levels range from −3.43 to −3.59 eV. Under AM 1.5 condition, the perovskite solar cell (PSC) with inverted p–i–n device structure using H7 as the dopant-free hole transporting material achieved a power conversion efficiency (PCE) of 12.1%, which is comparable to that using PEDOT:PSS as the hole transporting material (12.0%). Under an argon atmosphere, the PCE of H7-based PSC did not decay within 168 h, and it can retain 86.3% of its original PCE after 1000 h. The morphology study revealed that the film of H3–H7 was smooth and hydrophobic, while the perovskite film sp...