Solution‐Processed Organic Solar Cells with High Open‐Circuit Voltage of 1.3 V and Low Non‐Radiative Voltage Loss of 0.16 V

Compared with inorganic or perovskite solar cells, the relatively large non-radiative recombination voltage losses (ΔVnon-rad ) in organic solar cells (OSCs) limit the improvement of the open-circuit voltage (Voc ). Herein, OSCs are fabricated by adopting two pairs of D-π-A polymers (PBT1-C/PBT1-C-2Cl and PBDB-T/PBDB-T-2Cl) as electron donors and a wide-bandgap molecule BTA3 as the electron acceptor. In these blends, a charge-transfer state energy (ECT ) as high as 1.70-1.76 eV is achieved, leading to small energetic differences between the singlet excited states and charge-transfer states (ΔECT ≈ 0.1 eV). In addition, after introducing chlorine atoms into the π-bridge or the side chain of benzodithiophene (BDT) unit, electroluminescence external quantum efficiencies as high as 1.9 × 10-3 and 1.0 × 10-3 are realized in OSCs based on PBTI-C-2Cl and PBDB-T-2Cl, respectively. Their corresponding ΔVnon-rad are 0.16 and 0.17 V, which are lower than those of OSCs based on the analog polymers without a chlorine atom (0.21 and 0.24 V for PBT1-C and PBDB-T, respectively), resulting in high Voc of 1.3 V. The ΔVnon-rad of 0.16 V and Voc of 1.3 V achieved in PBT1-C-2Cl:BTA3 OSCs are thought to represent the best values for solution-processed OSCs reported in the literature so far.