Synthesis And Performance Of The Photovoltaic Materials Based On Thiophene-substituted Isoindigo

In this dissertation,the configuration and working principle of bulk heterojunction(BHJ)organic solar cells(OSCs)have been briefly introduced,and the research progress and design strategy of high-performance electron donor and electron acceptor materials in photoactive layers of BHJ OSCs are reviewed.The power conversion efficiency(PCE)of a OSC device is determined by the light harvesting capacity,energy levels,solubility,aggregation state,phase morphology,and carrier mobilities of the photoactive layer.Hence,a series of two-dimensional conjugated polymers based on benzo[1,2-b:4,5-b’]dithiophene(BDT)as electron-donating(D)units and thiophene-substituted isoindigo as electon-withdrawing(A)units,two small molecules with 3,3’-difluoro-2,2,-bithiophene as the core unit and thiophene-substituted isoindigo as two arms have been designed and synthesized by optimizing the structure in order to improve the light-harvesting capacity,molecular energy levels,solubility,crystallinity,microphase seperation structure and carrier mobility of the photosensitive materials.The intermediates and the products were characterized by MALDI-TOF MS,1H NMR and 13CNMR.Simultaneously,the thermal properties,optical properties,electrochemical properties,and crystallinity of the objective products have been systematically studied by TGA,UV-Vis,CV and WAXRD.Finally,the BHJ OSC devices based on these polymers and small molecules have been prepared,and the relationship between the molecular structure and photovoltaic properties have been also investigated.(1)Two A-D-A type small moleculs based on 3,3’-difluoro-2,2’-bithiophene as the central core and thiophene-substituted isoindigo derivitives as two arms have been designed and synthesized.The effects of monothiophene-and dithiophene-substituted isoindigo on the photophysical properties,electrochemical properties and molecular aggregation of the small molecules have been investigated.The results show that the small molecule S-TBIG based on monothiophene-substituted isoindigo derivitive as the arms possesses lower-lying highest occupied molecular orbital energy level,higher carrier mobility and stonger π-π stacking,so its OSCs exhibit a higher PCE value of 2.19%with a open-circuit voltage(Voc)of 0.69 V,a short-circuit current density(Jsc)of 6.50 mA cm-2 and a fill factor(FF)of 48.48%.(2)Two kinds of two-dimensional conjugated polymers,named as PBDT-TBIG and PBDTT-TBIG,have been designed and synthesized by using BDT derivitives as D units and mono thiophene-substituted isoindigo derivitives as A units on side chains.The effects of alkoxy(BDT)and alkylthienyl(BDTT)side chains of BDT derivitives on photovoltaic performance of the conjugated polymers have been also studied.The results indicate that the HOMO energy levels of the polymers can be depressed to under-5.32 eV and the Voc values can be improved to over 0.85 V.Simultaneously,PBDT-TBIG with alkoxy-substituted BDT derivitive as D units possesses higher hole mobility,smaller π-π stacking distance and more suitable blend film morphology,so its OSCs exhibit the highest PCE value of 5.87%,which is higher than the PCE values of the OSCs based on the reported polymers with thiophene-substituted isoindigo derivitives as A units.