Dichlorobenzodithiophene‐4‐8‐dione Derived Polymer Donor Enables Efficient Thin‐Film/Thick‐Film Organic Solar Cells
Han Liu, Qunping Fan, Kai Xiang, Ke Wang, Chenyang Dong, Xingpeng Liu, Yang Zhang, Xiong Li, Lihe Yan, Xinkang Wang, Tao Jia, Hairui Bai, Hongxiang Li, Qiang Tao, Jiangang Liu, Yuhang Liu, Chao Liang, Junwu Chen, Wei Ma, Wenyan SuABSTRACT
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.