Bilayer Quasiplanar Heterojunction Organic Solar Cells with a Co-Acceptor: A Synergistic Approach for Stability and Efficiency

Quasiplanar heterojunction (Q-PHJ) organic solar cells (OSCs) with a bilayer-type D/A phase distribution and a nanoscale bulk heterojunction (BHJ) region at the D/A interface have attracted significant attention for their efficient exciton dissociation and charge transfer to meet the demand for more efficient and stable photovoltaic devices. Herein, we demonstrate a co-acceptor-based Q-PHJ (co-Q-PHJ) OSC with enhanced crystallinity achieved by using two structurally compatible acceptors (BTIC-BO4Cl-βδ and ITCC). With a higher lowest unoccupied molecular orbital energy level and a wider band gap than BTIC-BO4Cl-βδ, ITCC can broaden the absorption range and support charge transfer for co-Q-PHJ devices. Consequently, when combined with D18 donor, the co-Q-PHJ OSCs fabricated with separately depositing donor and acceptor layers by using orthogonal solvents achieved a remarkable efficiency of 17.3%, which is much higher than that of the control ternary BHJ OSCs (16.0%). More importantly, the co-Q-PHJ device has a T80 lifetime of 612 h tested under 50 °C which is 5 times longer than that of the BHJ control device (∼110 h). The obvious increase in thermal stability and efficiency makes the co-Q-PHJ solar cells the basis of a practical strategy for the utilization of multi-component materials with strong crystallinities in such a real bilayer device structure.