Dichlorobenzodithiophene‐4‐8‐dione Derived Polymer Donor Enables Efficient Thin‐Film/Thick‐Film Organic Solar Cells

Polymer donors with electron-withdrawing benzodithiophene-4-8-dione (BDD) unit play an important role in improving power-conversion-efficiency (PCE) of organic solar cells (OSCs), although these achievements rely on high-cost electron-donating fluorinated thienyl-benzodithiophene (BDTT) moiety. Herein, a dichlorobenzodithiophene-4-8-dione (BDD2Cl) unit is developed to design fluorine-free BDTT-alt-BDD2Cl-structured cost-effective polymer donor (PBDTT-BDD2Cl). Compared to its halogen-free BDTT-alt-BDD-structured control (PBDB-T), PBDTT-BDD2Cl shows deep-shifted energy levels, improved solubility, crystallinity, and packing, tending to suppress energy loss, manipulate film-forming kinetics, and improve charge transport properties. Accordingly, the PBDTT-BDD2Cl:L8-BO device demonstrates dramatically higher photovoltage (0.947 V) and lower non-radiative energy loss (0.182 eV) and compared to the PBDB-T:L8-BO device (0.735 and 0.369 eV), while it achieves decreased PCE. When incorporating it into D18:L8-BO host, ternary D18:PBDTT-BDD2Cl:L8-BO shows optimized donor/acceptor miscibility, delayed material nucleation, and prolonged molecular ordered packing duration, leading to boosted charge dynamics and favorable morphology. Thereby, thin-film (100 nm) OSC achieves a superior PCE (21.1%, certified as 20.6%, ranking among the highest values) than the D18:PBDB-T:L8-BO control (19.3%), while its thick-film (500 nm) device also obtains a top-high PCE (17.3%) among these reported thick-films (≥500 nm). This work highlights that BDD2Cl is an ideal candidate for developing cost-effective polymer donors toward efficient thin-film/thick-film OSCs.