Synthesis And Properties Of Two-Dimensional (2D) Modified D-A Polymer Donors Based On Benzo[1,2-b:4,5-b'] Dithiophene (BDT)

As we all know,solar cells are a research hotspot in the energy field and an important topic that is difficult to overcome.As a new energy technology,organic solar cells have the advantages of light weight,wide absorption range,large-scale production through solvent processing and the manufacture of flexible and translucent devices.In recent years,a large number of organic solar cell active layer materials with novel structures and excellent performance have been developed.So far,the energy conversion efficiency(PCE)of organic solar cells based on non-fullerene acceptor materials has jumped to 18.20%,indicating the broad application potential of cost-effective and large area electricity production.This paper briefly describes the development of organic solar cells,and systematically summarizes and expounds the benzo[1,2-b:4,5-b']dithiophene(BDT)-based conjugated polymer donor materials.The effect of the conjugation effect and substitution position of the molecules on the photophysical,HOMO energy level,charge mobility and photovoltaic performance of organic solar cells were investigated.This paper provides a reference for the design of high-efficiency organic solar cells.The research contents and experimental results of this paper are summarized as follows:(1)In order to investigate the effects of substitution position on photovoltaic performance of donor polymers,two benzothiophene ring substituted benzo(1,2-b:4,5-b')dithiophene(BDT)-based conjugated polymers(PBDTBTs-BDD and PBDTTBs-BDD)are designed and synthesized.The optical band gaps of PBDTBTs-BDD and PBDTTBs-BDD are 2.08 e V and 1.97 e V,respectively.The effects of different substitution positions of the side chain alkyl chains on the molecular packing mode,morphological characteristics,absorption spectrum,electronic energy level,and various parameters of the photovoltaic performance of organic solar cells were studied.When using ITIC or Y6 as the acceptor materials,the PCE of PBDTBTs-BDD-based organic solar cells is 7.76% and 12.07%,respectively,and the PCE of PBDTTBs-BDD-based organic solar cells is 5.04% and 5.81%,respectively.(2)Based on the work of(1),we have designed and synthesized two kinds of polymer donors based on two benzothiophene ring substituted BDT units and fluorine(F)substitution thiophene[3,4-b]thiophene(TT)units.The TT unit was known for its stable quinone structure and wide application in designing low band gap polymers.The photophysical properties,electrochemical properties and photovoltaic properties of organic solar cells were systematically studied.It is found that introduction of the TT unit can enhance photon capture and charge collection capabilities,thereby increasing the short-circuit current of the device.With IT-4F as the acceptor materialls,the PCE of photovoltaic devices based on PBDTBTs-TT:IT-4F and PBDTTBs-TT:IT-4F are 6.43% and 7.06%,respectively.