Achieving Both Enhanced Voltage and Current through Fine-Tuning Molecular Backbone and Morphology Control in Organic Solar Cells

It is a great challenge to simultaneously improve the two tangled parameters, open circuit voltage (V_oc) and short circuit current density (J_sc) for organic solar cells (OSCs). Herein, such a challenge is addressed by a synergistic approach using fine-tuning molecular backbone and morphology control simultaneously by a simple yet effective side chain modulation on the backbone of an acceptor–donor–acceptor (A–D–A)-type acceptor. With this, two terthieno[3,2-b]thiophene (3TT) based A–D–A-type acceptors, 3TT-OCIC with backbone modulation and 3TT-CIC without such modification, are designed and synthesized. Compared with the controlled molecule 3TT-CIC, 3TT-OCIC shows power conversion efficiency (PCE) of 13.13% with improved V_oc of 0.69 V and J_sc of 27.58 mA cm⁻², corresponding to PCE of 12.15% with V_oc of 0.65 V and J_sc of 27.04 mA cm⁻² for 3TT-CIC–based device. Furthermore, with effective near infrared absorption, 3TT-OCIC is used as the rear subcell acceptor in a tandem device and gave an excellent PCE of 15.72%.