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%.