Doping a Main-Chain\nTwisted Wide Bandgap Bifunctional\nMolecule Enables Efficient Ternary Organic Solar Cells

The rapid development of organic solar cells (OSCs) has\nbeen particularly\nremarkable following the introduction of the high-performance small\nmolecule electron acceptor Y6 and its derivatives. Despite the advances\nin state-of-the-art OSCs, challenges remain, notably the relatively\nlow open circuit voltage (<i>V</i><sub>OC</sub>) and charge\nmobility imbalance, which continue to hinder further improvements\nin OSCs’ performance. To address these issues, in this work,\nwe synthesized a main-chain twisted wide bandgap small molecule <b>i-IEDTB</b>, which not only possesses superior hole mobility over\nelectron mobility but also has higher lowest unoccupied molecular\norbital (LUMO) energy levels, and adopted it as a bifunctional third\ncompound to couple with a high-performance terpolymer Z10 and Y6 based\nOSC system. The integration of <b>i-IEDTB</b> in the Z10:Y6\nblend, either as an acceptor or as a donor, significantly reduces\nthe excessive aggregation of Y6 and facilitates a harmonized distribution\nof electron and hole mobilities by modulating the crystallization\nproperties of the materials. This strategic intervention leads to\na marked improvement in <i>V</i><sub>OC</sub> and fill factor\n(FF). Consequently, the power conversion efficiency (PCE) of the optimized\nZ10:(Y6:<b>i-IEDTB</b>) ternary device is elevated to an impressive\n17.70%, surpassing the 16.50% of binary Z10:Y6 OSC. Besides, after\ndoping 5% weight <b>i-IEDTB</b> replaced that of Z10, the device’s <i>V</i><sub>OC</sub>, and FF were also increased to 0.846 V and\n78.08% respectively, resulting in an enhanced PCE of 17.47%. Further\ninvestigation demonstrates the universality of this molecule in PM6:BTP-eC9-based\nand PM6:L8-BO-based OSCs, achieving champion efficiencies of 18.14\nand 18.08%, respectively. This work highlights the key role of <b>i-IEDTB</b> as a bifunctional complementary component in modulating\nthe crystallographic order and carrier balance within the Y-type acceptor-based\nOSCs.