Optimized Morphology Enables High-Efficiency Nonfullerene Ternary Organic Solar Cells

Tuning the three-dimensional morphology in the active layer is an effective method to improve the performance of bulk heterojunction organic solar cells (OSCs). In this work, an acceptor-donor-acceptor structured small molecule ST10-CN-1 was synthesized and employed as the guest donor to fabricate ternary OSCs based on a PBDB-T:IT-M host binary system. The incorporation of ST10-CN-1 could broaden the active layer's absorption range of solar light thereby leading to a promotional short-circuit current. Moreover, adding an appropriate amount of ST10-CN-1 could effectively regulate the morphology of the active layer in both the lateral direction and vertical stratification. All of these morphological alterations helped to speed up the exciton dissociation, charge transit, and charge collecting processes, which in turn increased the power conversion efficiency. As a result, an excellent PCE of 11.5% for the ternary device based on PBDB-T:IT-M:ST10-CN-1 was obtained. The enhanced PCE was also linked to the formation of an alloylike state between PBDB-T and ST10-CN-1, as evidenced by the fact that the open circuit voltage of ternary OSCs lay between those for PBDB-T:IT-M (0.925 V) and ST10-CN-1:IT-M (1.064 V). This work illustrates that refining the morphology of the active layer by incorporating an appropriate third component is an effective way to further enhance the device's performance.

Automated summary

This study synthesized an acceptor-donor-acceptor structured small molecule ST10-CN-1 as the guest donor in ternary organic solar cells (OSCs) based on a PBDB-T:IT-M host binary system. Incorporating ST10-CN-1 broadened the absorption range of the active layer and improved the short-circuit current. Also, it regulated the morphology of the active layer and enhanced the exciton dissociation, charge transit, and charge collecting processes, leading to an excellent power conversion efficiency (PCE) of 11.5% for the ternary device. The formation of an alloylike state between PBDB-T and ST10-CN-1 contributed to the enhanced PCE.