Synthesis And Photovoltaic Properties Of Polymers Consisting Of Thiophene-benzene-thiophene And Diketopyrrolopyrrole

Bulk heterojunction(BHJ)polymer solar cells(PSCs)have been intensively studied in recent years for their low-cost,roll-to-roll production and environment friendly.Over the past decade,many studies have done in this field,the power conversion efficiency(PCE)of BHJ PSCs has improved significantly and that of single-junction BHJ PSCs have gradually exceeded 12%.Although progress has been impressive,further development of conjugated polymers is essential to achieve high-performance PSCs for commercialization.In such a background,we designed and synthesized three A-D-A terpolymer donor materials,three D-A-D terpolymer donor materials,as well as a series of novel polymer donor materials based on diketopyrrolopyrrole(DPP)side chain.The photophysical and electrochemical properties of the target polymers were researched.We have fabricated BHJ PSCs based on the target polymers,their photovoltaic performances were tested simultaneously.The main contents of this dissertation are as follows:1.Three conjugated terpolymers GP1,GP2 and GP3 based on thiophene-benzene-thiophene(TBT),4,7-dithien-5-yl-2,1,3-benzothiadiazole(BDTT)side chain,and DPP were synthesized.And the influences of the difference alkyl chain to the photophysical,electrochemical and photovoltaic properties were studied fully.The PSC device based on GP1 exhibits a low Jsc because of its largest lamellar distance and ?-? stacking distance.The polymer GP3 shows smaller lamellar distance and ?-? stacking distance,but its domain size is larger relatively.GP2 has an appropriate alkyl side chain,so it possesses more orderly ?-? stacking and broader absorption range and the appropriate microphase separation,which leads to higher PCE of 3.31%.2.Three conjugated terpolymers GP4,GP5 and GP6 based on TBT and alkylthienyl-substituted benzodithiophene(BDTT)as electron-rich units,DPP as electron-deficient unit were synthesized.Their photophysical,electrochemical and photovoltaic properties were tested.The optical,electrochemical properties,lamellar distance and ?-?* stacking distance of the random terpolymers were optimized by vary the ratio of TBT and DBTT.It was found that,as the TBT content increased,the?-? stacking distances decrease,but the HOMO level heighten,which lead to a highJsc and low Voc values.As a result,polymer solar cells based on GP5: PC61 BM blends(1 : 2,w/w)exhibited a high PCE of 4.18%.3.A new series of copolymers with one electron-rich unit BDTT and two electron-deficient units DPP and TTDPP building blocks were designed,synthesized,and their photophysical,electrochemical and photovoltaic properties were tested.We found that,as the TTDPP content increased,the absorption in the short-wavelength band enhanced,the ?-? stacking distances decrease and the HOMO level dropped,which lead to a high Voc values.As a result,polymer solar cells based on GP10:PC61BM blends(1: 2,w/w)exhibited a high PCE of 4.46%,indicating that the chemical structure of this conjugated random terpolymers composed of two different electron-deficient units is an effective approach to balance the Jsc and Voc of conjugated polymers for high performance PSCs.In addition,the optimizations on the GP8 device performance via solution(THF)vapor annealing were investigated.Exposure to THF vapor allows for a reorganization of the blend,which leads to optimal phase separation,a higher Jsc and PCE of 4.74%.