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 (V-OC) 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 V-OC 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 V-OC of 0.98 V owing to the stronger pi-pi stacking, more matched energy levels, and suppressed bimolecular recombination. Further fluorination of the p-type material, the PE62:F-Qx3b-based device obtained a V-OC as high as 1.09 V while achieving a slightly high PCE at 9.78% based on the Qx unit with a very high V-OC. These four devices maintain a high V-OC 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.

Automated summary

The study demonstrates the effectiveness of using the same acceptor unit to construct both donor and acceptor materials, achieving high efficiency and higher open-circuit voltage by fine-tuning optoelectronic properties through the introduction of fluorine atoms.