Hybrid central substitution of acceptors boosts the efficiency of near-infrared organic photovoltaics

Abstract

Near-infrared (NIR) organic photovoltaic molecules are usually restricted by the “energy-gap law”, making it greatly challenging to simultaneously achieve organic solar cells (OSCs) with a high open-circuit voltage (V_OC) and NIR absorption. Herein, a synergistic strategy involving the hybrid central substitution on acceptors with an electron-donating methyl/methoxy group was developed, allowing NIR absorption with the electron-withdrawing bromine inducing favorable molecular packing. Single-crystal analysis revealed the rarely observed OC–H⋯S non-covalent interaction and potentially beneficial entanglement of alkyl chains in CH29 with a central methoxy group. Consequently, an OSC fabricated with CH29 achieved an excellent V_OC of 884 mV and a short-circuit current density of 28.30 mA cm⁻² under a quite narrow optical bandgap of ≈1.33 eV while showing an almost minimal energy loss. Our successful attempt at hybrid central substitution provides a feasible pathway to construct high-performance NIR acceptors, which are essential to obtaining record-breaking OSCs, especially for the rear cells of tandem devices that simultaneously require high V_OC and a broad photoelectric response.