Organic Photovoltaic Cells Based on Nonhalogenated Polymer Donors and Nonhalogenated A-DA′D-A-Type Nonfullerene Acceptors with High V_OC and Low Nonradiative Voltage Loss

Compared with other all-inorganic/organic–inorganic hybrid solar cells, the large voltage loss (Vloss) of organic photovoltaic (OPV) cells, especially the nonradiative voltage loss (ΔVnonrad), limited the further improvement of performance. Although A-DA′D-A-type Y-series nonfullerene acceptors (NFAs) largely improve the power conversion efficiencies (PCEs) to 18%, the open-circuit voltage (VOC) of this kind of material was still restricted to below 1.0 V. Herein, we designed and synthesized a narrow bandgap (Eg = 1.41 eV) acceptor BTA77 with an A-DA′D-A-type backbone containing a nonhalogenated terminal group to achieve high electroluminescence efficiency and high VOC. Combined with the nonhalogenated polymer PBDB-T with a conjugated thiophene side chain, BTA77 realized a VOC of 0.944 V, a Vloss of 0.552 V, and a PCE of 13.75%, which is one of the highest PCEs based on nonhalogenated A-DA′D-A-type acceptors with VOC > 0.9 V. After further blending with the nonhalogenated donor polymer PBT1-C with a conjugated phenyl side chain, the VOC increases to 1.021 V with a super low ΔVnonrad of 0.14 V owing to the greatly improved electroluminescence external quantum efficiency (EQEEL) of 4.42 × 10–3. Our results indicate that there is still a large room to decrease the ΔVnonrad and increase VOC by synergistic molecular engineering of p-type polymers and n-type small molecules.