Superior charge dynamics via ternary doping layer-by-layer strategy in high-efficiency organic solar cells

Nowadays, the preparation of pseudo-planar heterojunctions (P-PHJ) using the layer-by-layer (LbL) method has aroused considerable interest due to its merits in increasing the dimensions of pure domains and establishing vertical phase distribution, which is favorable for charge transport. However, the excessive pure domain scale can easily be generated in P-PHJ, thereby lowering the exciton dissociation efficiency. In this study, a ternary doping layer-by-layer (D-LbL) strategy is proposed to prepare the active layer of D + A2/A1 + D structure, where D18 is donor (D), L8-BO is acceptor 1 (A1), and BTP-eC9 is acceptor 2 (A2). A series of characterizations shows that the interpenetrating network structure and molecular crystallinity of the active layer are significantly optimized via the ternary D-LbL strategies, which ensures both exciton dissociation efficiency and charge transport efficiency. The organic solar cells (OSCs) based on D + A2/A1 + D exhibits an excellent photoelectric conversion efficiency of 19.37 % along with a high open-circuit voltage of 0.913 V, a superior short-circuit current density of 26.99 mA cm-2 and an excellent fill factor of 78.62 %, which is much superior to that of the binary P-PHJ OSCs (17.77 %). This work demonstrates that the ternary D-LbL strategy is an excellent approach for optimizing the active layer morphology to achieve outstanding charge dynamics.