Constructing ternary double bulk heterojunction organic solar cells via layer-by-layer deposition method

Abstract

The layer-by-layer (LbL) deposition method has become an effective strategy to prepare the active layer in organic solar cells (OSCs). In this research, the ternary double-bulk heterojunction (double-BHJ) OSCs based on PM1:BTP-eC9/PM1:L8-BO are prepared by the LbL deposition method. The highly crystalline BTP-eC9 at the bottom acts as crystalline seeds, which facilitate the formation of a more ordered molecular arrangement and higher crystallinity for the double-BHJ active layer compared to the PM1:L8-BO active layer. The excellent compatibility between L8-BO and BTP-eC9 partially drives BTP-eC9 in the bottom layer to approach L8-BO in the top layer during the top layer PM1:L8-BO spin-coating process, which facilitates the formation of donor/acceptor (D/A) bicontinuous interpenetrating networks. The optimized morphology effectively reduces non-radiative recombination energy loss in the double BHJ OSC, achieving a higher open-circuit voltage (V_OC). Ultimately, a power conversion efficiency (PCE) of 19.62% for the ternary double-BHJ OSCs is obtained, which is excellent compared to the 18.18% for OSCs based on PM1:L8-BO and 17.11% for OSCs based on PM1:BTP-eC9. This work shows that constructing the double-BHJ OSCs using the LbL deposition method is an effective strategy for obtaining excellent active layer morphology, which can offer an effective approach to enhance the performance of multi-component OSCs.