The Insolubility Problem of Organic Hole-Transport Materials Solved by Solvothermal Technology: Toward Solution-Processable Perovskite Solar Cells

Generally, the high efficiency of solution-processable perovskite solar cells (PSCs) comes at the expense of using expensive organic matters as a hole-transport material (HTM). Although intense efforts have tried to use commercially available and low-cost macrocyclic molecules as HTM candidates, they still face two enormous challenges: poor solubility and inherent instability. Here, solvothermal treatment for old and insoluble HTMs (phthalocyanine (Pc) and its derivatives) has been proposed, which is unusual due to the occurrence of solubilization for insoluble precursors induced by the carbonization of the dissolved part. Since the macrocyclic structure still exists, the as-prepared new-type carbon dots not only retain the capacity of hole transfer but serve as an effective passivation additive. Synergy makes the all-air-processed carbon-based PSCs (CH3NH3PbI3) fabricated with carbon dots achieve a decent power conversion efficiency of 13.7%. Importantly, organics have undergone solvothermal treatment, completely breaking through the instability bottleneck, which exists in the long-term operation of PSCs. The universality of this methodology will usher exploration into other low-cost insoluble organics and drastically enhance the high-performance cost ratio of PSC equipment.