A Large-Bandgap Guest Material Enabling Improved Efficiency and Reduced Energy Loss for Ternary Polymer Solar Cells

The rational design of guest photovoltaic materials (the third components) for enhancing the power conversion efficiency (PCE) of ternary polymer solar cells (PSCs) is a challenge. In this work, a large-bandgap material ((5Z,5 ' Z)-5,5 '-(((4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-b:5,6-b ']dithiophene-2,7-diyl)bis(2,5-difluoro-4,1-phenylene))bis(methanylylidene))bis(3-ethyl-2-thioxothiazolidin-4-one, IBR-F) is designed, synthesized, and used as the guest material for ternary PSCs to improve the PCE and reduce the energy loss. IBR-F possesses a larger energy bandgap of 2.04 eV and a deeper highest occupied molecular orbital (HOMO) level compared to PM6, as well as exhibiting good miscibility with PM6. Thus, the HOMO level is effectively downshifted when blending PM6 with IBR-F, which is in favor of obtaining a higher open-circuit voltage (V-oc). Meanwhile, the incorporation of IBR-F into the PM6:Y6 blend can maintain the well-developed bulk-heterojunction morphological properties of the host blend without extra thermal annealing and improve the charge dissociation and collection efficiencies. As a result, the ternary PSC based on PM6:IBR-F:Y6 (1:0.2:1.2 w/w) demonstrates a higher V-oc of 0.887 V and a reduced energy loss of 0.55 eV compared to the binary device based on PM6:Y6 (1:1.2 w/w) with a V-oc of 0.840 V and energy loss of 0.59 eV, delivering an improved PCE of 17.15%.

Automated summary

The study involves the rational design and synthesis of a large-bandgap material IBR-F for ternary PSCs, which leads to an improved PCE and reduced energy loss. Experimental results demonstrate that the incorporation of IBR-F results in higher Voc, lower energy loss, and significantly improved PCE in the ternary PSCs.