Effects of solvent additives on the morphology and transport property of a perylene diimide dimer film in perovskite solar cells for improved performance

Perylene diimide derivatives (PDIs) are a kind of very promising non-fullerene electron transport material for organic-inorganic perovskite solar cells (PerSCs), owing to their excellent photoelectric properties and low-cost synthesis. However, their tendency to form aggregates strongly influences the film morphology and transport properties. Herein, we provided a simple way to tune the morphology and transport properties of PDIs by solvent additive engineering. A series of solvent additives (1,8-diiodooctane, 1-chloronaphthalene, 1-phenylnaphthalene, 1-methylnaphthalene) was investigated for their role in the morphology and transport property of PDI dimer (Bis-PDI-T-EG) film as well as on the photovoltaic performance of PerSCs. Among these four solvent additives, 1-methylnaphthalene (MN) was found one of the best additive that possesses good adjusting ability to control both morphological and electrical properties of Bis-PDI-T-EG film. The fabricated PerSCs with optimized Bis-PDI-T-EG + 0.05 v/v% MN electron transport layer (ETL) displayed the best power conversion efficiency (PCE) of 14.96%. The performance of PerSCs was further improved by adding 0.05 wt% graphene together with 0.05 v/v% MN, and the maximum PCE of 15.11% was achieved.