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In the past few years, fluorine atom has been widely introduced into organic semiconductor (OS) materials to improve the photovoltaic performance of polymer solar cells (PSCs). In contrast, chlorine atom is rarely concerned, although it is also a halogen element and is more easily introduced into OS materials. Herein, we designed and synthesized a new D-A-type two-dimension (2D)-conjugated polymer, PM7, containing a chlorinated-thienyl benzodithiophene (BDT-2Cl) donor unit and a benzodithiophene-4,8-dione acceptor unit. Compared to the control polymer PBDB-T without chlorine substitution, PM7 shows lower HOMO energy level, higher absorption coefficient, enhanced crystallinity and higher carrier mobility. Moreover, the toluene-processed PSCs based on PM7 as donor and small molecule n-OS IT-4F as acceptor achieved a high power conversion efficiency (PCE) of 13.1% with high open-circuit voltage (Voc) of 0.88 V, short-circuit current density (Jsc) of 20.9 mA cm−2 and fill factor (FF) of 71.1%, while the PBDB-T:IT-4F-based PSC only exhibited a low PCE of 5.8% with low Voc of 0.67 V, Jsc of 15.0 mA cm−2 and FF of 57.6%. The PCE of 13.1% is among the highest values reported for the PSCs to date. These results indicate that the chlorine substitution is a simple and effective strategy to design high-performance conjugated polymer photovoltaic materials.

In addition to high power conversion efficiency (PCE) and good stability, the low-cost of photovoltaic materials is also very important for the practical application of organic solar cells (OSCs). Herein, we synthesized a carboxylate substituted pyrazine-based electron-deficient building block (DTCPz) with a simple structure and low synthetic cost, and then developed a novel wide bandgap polymer donor PFBCPZ. Due to the synergistic electron-withdrawing effects of the fluorination in donor unit (BDT-TF) and esterification and C=N double-bond in DTCPz unit, PFBCPZ shows a deeper HOMO level of −5.60 eV, a strong intermolecular π-π interaction, good crystallinity and stacking, and high hole-mobility of 2.11 × 10−3 cm2 V−1 s−1. Matched with a low bandgap acceptor IT-4F, excellent charge transfer, weak recombination, and small non-radiative energy loss in OSCs was achieved, resulting in an impressive fill factor of 0.785 and a high open-circuit voltage of 0.92 V. As a result, a PCE of up to 15.3% is obtained in OSCs, which is the highest value in the IT-4F-based binary OSCs so far and indicates that low-cost DTCPz with a simple structure is a promising building block to construct high-performance polymer donors for application in efficient OSCs.