From spin coating to doctor blading: A systematic study on the photovoltaic performance of an isoindigo-based polymer

Doctor blading is suitable to roll-to-roll process with much little solution wasting and is less studied compared with the mainstream spin coating. In this work, we used a novel polymer blended with two common fullerene derivatives as active solutions. To systemically understand the different coating methods and the different fullerene acceptors on the effect of polymer solar cells (PSCs) photovoltaic performance, the wet active solution physic-chemical properties and variations of the dried active layer characterizations were investigated. It was observed that it is much easier to obtain a homogeneous film from doctor blading compared with spin coating for the polymer: PC71BM solution due to the high surface tension and viscosity. Moreover, the high boiling point additive plays an important role in inhibiting the wet film shrinkage and forming a uniform film. The longer film drying time for the doctor-blading films leads to larger domains than spin coating, thus increases the geminate recombination and results in lower mobilities as well as power conversion efficiencies (PCE). Doctor-blading-processed PSCs with PCE of 4.46% were achieved for P3TI:PC71BM devices, which were comparable to those of spin-coating devices. This work provided valuable suggestions and solutions for the doctor-blading process, especially for crystalline D-A polymer-based devices.