Over 19.2% Efficiency of Layer-By-Layer Organic Photovoltaics by Ameliorating Exciton Dissociation and Charge Transport

Layer-by-layer (LbL) organic photovoltaics (OPVs) are fabricated with polymer PM1 as donor and small molecule L8-BO as acceptor by employing sequential spin-coating technology. The small molecule BTP-eC9 and polymer PTAA are deliberately selected for individually incorporating into PM1 layer and L8-BO layer, resulting in the power conversion efficiency (PCE) increased from 18.22% to 19.23%. The improvement of performance is attributed to the synergistically increased short circuit current density (J_SC) of 27.78 mA cm⁻² and fill factor (FF) of 78.23%. The introduction of BTP-eC9 into PM1 layer can promote the photogenerated exciton dissociation, especially for the excitons near the anode. Meanwhile, molecular crystallinity of PM1 is also enhanced by incorporating appropriate BTP-eC9 into PM1 layer. The incorporation of PTAA into L8-BO layer can provide hole transport channels to effectively improve the transport of holes generated by the self-dissociation of L8-BO, resulting in the enhanced FFs from 77.40% to 78.23%. The synergistic effects of BTP-eC9 and PTAA incorporation in donor and acceptor layers result in a 19.23% PCE of the optimized LbL-OPVs. This work demonstrates that there is great room to hierarchically optimize donor and acceptor layers for achieving highly efficient LbL-OPVs.