An investigation of annealing methods for benzodithiophene terthiophene rhodanine based all small molecule organic solar cells

Mainstream organic solar cells (OSCs) suffer a great variation of photovoltaic performance among different batches of polymers, which brings an opportunity for all-small-molecule OSCs to take leading position of industrialization. In recent years, benzodithiophene terthiophene rhodamine (BTR), as small molecule donor, has played an important role in this field. Here we investigated two typical BTR based all-small-molecule OSCs processed with different annealing methods, to explore the morphology optimization brought by them. As a result, BTR:PC71BM system was optimized by solvent vapor annealing (SVA) reaching an excellent fill factor (FF) of 79.1% via tuning molecular packing intensity, while BTR:Y6 with temperature annealing (TA) yielded a power conversion efficiency (PCE) of 12.125% whose molecular packing orientation had been changed. Additionally, by crossing using SVA and TA methods, we found that these two method can't be utilized together to further improve the PCE for either system. Therefore, our work offers better PCEs for these two reported combinations and further studies the compatibility between specific BTR based active layers and designated annealing methods, providing deeper understanding of device engineering on all-small-molecule OSCs.