Synthesis And Properties Study Of Non-fullerene Acceptors Based On Benzothiadiazole

As the energy crisis and environmental pollution become increasingly severe,how to efficiently utilize clean and pollution-free energy has become an important issue in the society.In this regard,the development and utilization of solar energy is of great significance.Over the past decade,the photovoltaic performance of organic solar cells（OSCs）has made significant progress,and their power conversion efficiency has reached commercialization requirements,gradually developing into a practical photovoltaic technique.The rapid development of OSC efficiency in recent years is mainly due to the design and development of efficient non-fullerene acceptor materials.Among them,the A-D-A structure with an electron-donating central core unit and electron-withdrawing end capping units（A）is one of the most efficient non-fullerene acceptor structures that have been explored.Based on this structural feature,the absorption spectrum and energy level structure of the non-fullerene acceptor can be effectively adjusted by changing the structure of the central core unit,thereby affecting the optoelectronic properties and the final photovoltaic performance of the device.In this paper,we designed and synthesized two new non-fullerene acceptor molecules by adjusting the structure of the central core unit,and systematically characterized their absorption properties,electrochemical properties,and photovoltaic performance.The results and conclusions are as follows:In the second chapter,the benzodithiophene unit is used as the core unit of the non-fullerene acceptor（target）molecule,then the conjugated length of the core structure is extended by connecting thiophenes on both sides of the benzodithiophene through the Still coupling reaction.Finally the A-D-A type non-fullerene acceptor BDT-IC molecule was designed and synthesized by coupling with the indanone terminal unit through the Knoevenagel condensation reaction.The BDT-IC molecules exhibit broad absorption（300 nm-800 nm）no matter in dilute solution or thin film state.The LUMO energy level of BDT-IC is-3.85 e V,and the HOMO energy level is-5.40 e V measured by electrochemical cyclic voltammetry.The active layer was prepared by blending BDT-IC as acceptor and polymer PBDB-T as donor.The photovoltaic performance of the device was improved by optimizing the donor-acceptor weight ratio and solvent additives conditions.The results show that the power conversion efficiency of the device reaches 14.54%at the donor-acceptor weight ratio of 1:2 and the 0.5%v/v DIO additive.In the third chapter,the non-fullerene acceptor BDT-BT-IC molecule was designed and synthesized by selecting benzodithiophene-benzothiadiazole coupling as the D-A-D type conjugated molecular skeleton,and the fluorine-substituted indanone structural unit as the terminal group.The BDT-BT-IC molecule exhibits broad absorption（400 nm-900 nm）in the thin film state,and the maximum absorption peak is at 755 nm.Electrochemical test results show that the BDT-BT-IC molecule has a lower HOMO energy level and a narrower bandgap than the BDT-IC molecule.The active layer was prepared by blending the BDT-BT-IC with PBDB-T polymer,which is complementary to BDT-BT-IC in absorption and well-matched in energy level.The photovoltaic performance of the device was improved by optimizing the additives and the annealing conditions when fabricating the active layer.The optimized device shows high external quantum efficiency（EQE）in the range of 300 nm-900 nm,with a maximum EQE exceeding 90%.The maximum electron mobility based on PBDB-T:BDT-BT-IC composite film reaches 1.70×10^-3 cm²/Vs.