Fluorination of the Quinoxaline-Based p-Type Polymer and n-Type Small Molecule for High VOC Organic Solar Cells

The "Same-A-Strategy" (SAS) employing the same acceptor unit (A) to construct both donor and acceptor materials was effective to achieve high open-circuit voltage (VOC) but only confined to the benzotriazole (BTA) unit. In this work, we chose quinoxaline (Qx) instead of BTA as the A unit to construct photovoltaic materials and extended the application of the SAS. By introducing the fluorine atom to the thiophene side chains of the p-type polymer and Qx units of the n-type small molecule, the optoelectronic properties can be effectively fine-tuned. The photovoltaic device based on PE61:Qx3b achieved a power conversion efficiency (PCE) of 8.24% with a VOC of 1.02 V. After fluorination of the n-type material, the PE61:F-Qx3b-based device achieved an improved PCE of 10.45% with a medium VOC of 0.98 V owing to the stronger π–π stacking, more matched energy levels, and suppressed bimolecular recombination. Further fluorination of the p-type material, the PE62:F-Qx3b-based device obtained a VOC as high as 1.09 V while achieving a slightly high PCE at 9.78% based on the Qx unit with a very high VOC. These four devices maintain a high VOC around 1.0 V with a low energy loss from 0.57 to 0.71 eV. Our results indicate that the Qx unit is also appropriate for the SAS to attain high-voltage solar cells, and fluorination is helpful to promise performance.