Fused selenophene-thieno[3,2-B] thiophene-selenophene (ST)-based narrow-bandgap electron acceptor for efficient organic solar cells with small voltage loss

A novel near-infrared-light-absorbing fused-ring electron acceptor, STIC, was developed for organic solar cells. STIC exhibited a narrow bandgap with an absorption edge reaching 940 nm, which was ascribed to the strong electron-rich selenophene-thieno[3,2-b]thiophene-selenophene (ST) unit and strong intramolecular charge transfer of STIC. Also, STIC-based devices showed low open-circuit voltage (V_oc) loss values, attributed to the rigid ST core providing low reorganization energy. The device based on the PBDB-T:STIC blend exhibited a power conversion efficiency (PCE) of 9.68% with a high short-circuit current density (J_sc) of 19.96 mA cm^-2 and a low V_oc loss of 0.55 eV.