Synthesis And Photovoltaic Properties Of Polymers Based On Bithiophene Bridged Benzo-thiadiazole

Solar cells are devices that generate electricity through the photovoltaic effect of materials,which are the long-awaited renewable clean energy for human beings.The power conversion efficiency of organic solar cells has now exceeded 14%after 20 years of development,showing excellent potential for applications.Studies have shown that high-performance donor materials should have absorption spectra matching the solar spectrum,higher carrier mobility,suitable energy levels,better film-forming properties and with the receptor to form the appropriate nano-scale interpenetrating network structure.However,it is necessary to improve the solar cell photo-stabilities,power conversion efficiency,life expectancy and other properties.In this dissertation,ten alternating medium band gap conjugated polymers derived from 4,8-bis(4,5-dioctylthien-2-yl)benzo[1,2-b:4,5-b']dithiophene(BDT-T)or 5,10-bis(4,5-didecylthien-2-yl)dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene(DTBDT-T)are synthesized and characterized.The thermal stabilities,photo-stabilities,optoelectronic properties etc.of the polymers were investigated.In chapter 3,using 4,8-bis(4,5-dioctylthien-2-yl)benzo[1,2-b:4,5-b']dithiophene(BDT-T)electron donor units and modified benzothiadiazole units as electron acceptor units,the copolymers PBDT-BT-TT,PBDT-BT-FTT,PBDT-FBT-TT and PBDT-FBT-FTT are synthesized and characterized.After 10 h of irradiation,the polymers maintained 84%,83%,83%and 78%of its initial light absorption at the maximal absorption peaks,respectively.The photocurrent response ranging from 300 nm to 800 nm,and the maximum absorption peaks of the polymer are 601 nm,598 nn,566 nm and 613 nm,respectively.Furthermore,the highest molecular orbital energy level(EHOMO)are-5.38 eV,-5.45 eV,-5.52e V and-5.55 eV,respectively.The lowest molecular unoccupied orbital energy level(ELUMO)are-3.60 eV,-3.75 eV,-3.75 eV and-3.87 eV,respectively.Going through the varied preparation optimization methods of device,the solution additive DIO can significantly separate the active layer film,greatly increasing the Js,and FF.Thus the photoelectric conversion efficiency of PBDT-BT-TT,PBDT-BT-FTT,PBDT-FBT-TT,and PBDT-FBT-FTT were 4.47%,2.31%,1.43%,and 2.56%,respectively.In chapter 4,based on the monomers synthesized in the 3 chapter,we developed four novel CPs(respectively named as PDTBDT-BT-TT and PDTBDT-BT-FTT,PDTBDT-FBT-TT,PDTBDT-FBT-FTT)by copolymerizing 5,10-bis(4,5-didecylthien-2-yl)dithieno[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']-dithiophene(DTBDT-T)by Stille cross-coupling reaction.After 10 h of irradiation,the polymers maintained 83%,82%,82%and 77%of its initial light absorption at the maximal absorption peaks,respectively.The photocurrent response ranging from 300 nm to 800 nm,and the maximum absorption peaks of the polymer are 604 nm,600 nm,573 nm and 614 nm,respectively.Moreover,the highest molecular orbital energy level(EHOMO)are-5.32 eV,-5.41 eV,-5.48 eV and-5.49 eV,respectively.The lowest molecular unoccupied orbital energy level(ELUMO)are-3.63 eV,-3.74 eV,-3.73 eV and-3.82 eV,respectively.Meanwhile,under the condition of AM 1.5G 100 mW/cm2,the PCEs of the optimal devices based on PDTBDT-BT-TT,PDTBDT-BT-FTT,PDTBDT-FBT-TT and PDTBDT-FBT-FTT were 3.87%,3.06%,1.50%,and 5.28%,respectively.In Chapter 5,Two conjugated polymers(PBDT-TPTI and PDTBDT-TPTI)derived from 4,8-bis(4,5-dioctylthien-2-yl)benzo[1,2-b:4,5-b']dithiophene and 5,10-bis(4,5-didecyl-thien-2-yl)dithieno-[2,3-d:2',3'-d']benzo[1,2-b:4,5-b']dithiophene with pentacyclic aromatic lactam of N,N-didodecylthieno[2',3':5,6]pyrido[3,4-g]thieno[3,2-c]-iso-quinoline-5,11-dione(TPTI),are synthesized and characterized.At the same time,the Inverted solar cell from the blend films of PBDT-TPTI and PDTBDT-TPTI with PC71BM,presented higher PCEs of 5.98%and 6.05%compared to the PCEs of 4.48%from P3HT/PC71BM under AM 1.5G 100mW/cm2.The power conversion efficiency of the inverted photovoltaic cells from PBDT-TPTI and PDTBDT-TPTI were increase to 7.58%and 6.91%.The photocurrent responses of the devices response were between 300 nm and 792 nm,when the ITIC was served as electron acceptor materials.