Synthesis And Photovoltaic Properties Of Organic Solar Cell Donor/Acceptor Materials Based On Thieno[3,2-b] Thiophene

The development of clean energy such as solar energy becomes essential,since the fossil energy is non-renewable and has brought severe environmental issues during the exploration and conversion.Organic solar cells?OSC?have attracted wide attention as they show advantages in diversity of material structures,flexibility,translucent or transparent device,and low-cost for large-area printing of device.In 1995,Heeger's group fabricated the bulk heterojunction?BHJ?solar cell.Since then,the exploration of high performance electron donor and acceptor have been the focus in this area.The electron donors can be polymer or small molecule,and the electron acceptors are categorized into fullerene acceptors?FAs?and non-fullerene acceptors?NFAs?.While FAs show good electron mobility,they have drawbacks such as weak absorption in visible and NIR regions,low LUMO energy levels,limitation of electronic energy level adjustment,and poor stability of devices.The development of NFAs is a key strategy to solve these problems.In this thesis,we design and synthesize four polymer donors and two small-molecule NFAs,which are then respectively matched with appropriate acceptors and donors to fabricate BHJ-OSCs.Chapter 1:Research background and design rationale.Firstly,we give a brief summary on the working principle and historic development of OSCs.Then,we introduce the recent progress of OSCs materials.Finally,we give the design rationale of this thesis.Chapter 2:Design and synthesis of wide bandgap polymer donors based on BDT.In order to gain insight into the influence of atoms?H,Cl,F?on the photovoltaic performance of BDT-based OSCs,we designed and synthesized three wide bandgap polymer donors PHL4,PHL5,and PHL9 respectively employing H-BDT,Cl-BDT and F-BDT as electron-donating moiety.IT-4F was selected as acceptor to fabricate the BHJ-OSCs with PHL4,PHL5,and PHL9.The BHJ-OSCs made from PHL5 and IT-4F show good performance with power conversion efficiency?PCE?of 9.0%,open circuit voltage(V_OC)of 0.79V,short-circuit current(J_SC)of 18.5 mA cm^-2,and fill factor?FF?of 61.5%.Chapter 3:Design and synthesis of symmetric medium bandgap polymer donors.On the basis of PHL4,the electron-withdrawing unit was changed to give a symmetric medium bandgap donor PHL11.The narrow band gap acceptor COi8DFIC was selected as acceptor to fabricate BHJ-OSC with PHL11.The resulting BHJ-OSC shows better performance those in Chapter 2,i.e.,PCE of 11.88%,V_OC of 0.70 V,J_SC of 25.94 mA cm^-2,and FF of 65.2%.Chapter 4:Design and synthesis of small molecule NFAs.Two small molecule NFAs,PHL15 and PHL19,were synthesized by employing alkoxy/alkythio thiophenes as electron-donating units and DF-IC as electron-withdrawing unit.We have fabricated a series of HBJ-OSCs by selected various electron donor materials to mix with PHL15and PHL19.It was found that the HBJ-OSCs of PHL15 and LJF3 showed the best performance with PCE of 6.9%,V_OC of 0.79 V,J_SC of 15.20 mA cm^-2,and FF of 57.1%.On the other hand,PHL19 is not suitable for the fabrication of HBJ-OSCs owing to the poor solubility.