Hybrid nonfullerene acceptor merged from IT-4F and Y6 for efficient organic solar cells

Over the last decade, power conversion efficiencies (PCEs) of organic solar cells (OSCs) have grown double to ∼20 %, which primarily originates from the development of non-fullerene acceptors (NFAs). Up to now, ITIC- and Y-series NFAs remain the most successful acceptor materials, with IT-4F and Y6 molecules being their representative compounds, respectively. Herein, a hybrid NFA TITT-2F, integrating structural features of both IT-4F and Y6, was developed, which is based on thieno[2′,3':4,5]thieno[3,2-b]indole-thieno[3,2-b]thiophene core incorporating a spiro group. As a result, TITT-2F exhibits medium crystallinity and absorption spectrum with a low optical bandgap of ∼1.44 eV, a planar molecular geometry, and suitably-aligned energy levels. An OSC based on PM6:TITT-2F afforded a respectable PCE of 12.16 %. Furthermore, a ternary PM6:5 %TITT-2F:95 %Y6 cell exhibited a promising PCE of 16.37 % with a V_OC of 0.86 V, a J_SC of 26.74 mA/cm², and a fill factor (FF) of 71.56 %. These enhancements are attributed to balanced charge carrier mobilities, efficient exciton dissociation, and face-on orientation in blend films. These findings demonstrate that hybrid NFAs hold a great potential for well-performed OSC applications.