Increased performance of A-DA’D-A type acceptor based organic solar cell using a thermally coevaporated cathode-modifying blend layer

Abstract The blend thin films of bathocuproine and fullerene (BCP:C 60 ) have been thermally coevaporated to modify the active layer/cathode interfaces in organic solar cells. The BCP forms a much smaller-barrier contact with cathode than the C 60 . Because the surface zone of active layer is polymer donor-rich and small-molecular acceptor-deficient, C 60 molecules make insufficiently large contact area with electron acceptor, leading to inefficient electron extraction. However, BCP molecules penetrate the surface of active layer, due to the smaller molecular size of BCP than that of C 60 , and likely form sufficiently large contact area with electron acceptor thereby to enable efficient electron extraction. Compared to conventional 10 nm BCP, 10 nm BCP:C 60 (1:1 in mass ratio) enables higher efficiency based on the active layer using A-DA’D-A type acceptor, mostly because C 60 constituent dissociates some excitons photogenerated in the polymer donor of surface zone and thereby increases short-circuit current density. The current research provides novel insights into the development of cathode-modifying layers for organic solar cells.