Synthesis And Photovoltaic Characterization Of Polymers Based On Alkylthienothiophene-dithienobenzodithiophere

As the traditional energy sources dried up and increasing deterioration of the environment, the development and utilization of new energy is a problem which needs to be solved urgently. In recent years, polymer solar cells（PSCs） have become a research hotspot with the excellent advantages, such as low price, good flexible, light weight, easy to modify, etc. However, the power conversion efficiency of PSCs is relatively low, the design and synthesis of excellent performance PSC materials has a very important meaning for the development and utilization of solar energy.In this paper, by the modification of the benzo[1,2-b:4,5-b’]dithiophene（BDT） as the electron donor unit, we have synthesized a new type of electron donor unit 4,8-bis[（5-butyloctyl）thieno[3,2-b]thiophene-2-yl]benzo[1,2-b:4,5-b’]dithiophene（BDT-TTBO） which has two-dimensional polycyclic structure with a greater conjugated degree. Using BDT-TTBO as the donor unit, we selected electron acceptor units showing excellent performance, and synthesized a series of donor-acceptor（D-A） conjugated polymers through the Stille reaction. Finally, the obtained conjugated polymers were characterized and their photovoltaic performance were investigated. The main contents of this thesis were as following,1. Chapter 2, alkyl-thieno[3,2-b]thiophene was introduced to the backbone of BDT, two-dimensional structure of BDT derivative electron donor unit, namely, 4,8-bis [（5-butyloctyl）thieno[3,2-b]thiophene-2-yl]benzo[1,2-b:4,5-b’]dithiophene（BDT-TTBO） was synthesized. By Stille coupling reaction between the abovementioned monomers and benzo[1,2,5]thiadiazole and 5,6-difluorobenzo[1,2,5]thiadiazole, two polymers, namely PBDT-TTBO-BT and PBDT-TTBO-FBT were synthesized, respectively. The resulted copolymer PBDT-TTBO-BT showed the optical band gap of approximately 1.69 eV, EHOMO and ELOMO of-5.46 eV and-3.81 eV. The device was prepared by using PBDT-TTBO-BT as donor material and PC₆₁ BM as acceptor material, the highest power conversion efficiency（PCE） was 1.19%(V_OC = 0.79 V,J_SC = 4.26 mA/cm²,FF = 35.40%). By the contrast, the containing fluorine copolymer PBDT-TTBO-FBT exhibited the optical band gap of about 1.70 eV, EHOMO and ELOMO of-5.53 eV and-3.88 eV. And the device was finished by using PBDT-TTBO-FBT as donor material and PC₆₁ BM as acceptor material, the highest PCE was 1.67%(V_OC =0.82 V,J_SC = 5.62 mA/cm²,FF =36.31 %).2. Chapter 3, the monomer 4,7-bis（5-bromo-2-ethylhexyl thiophene）benzo[1,2,5] thiadiazole（DTBTEH） and 4,7-bis（5-bromo-2-ethylhexyl thiophene）-5,6-difluorobenzo[1,2,5] thiadiazole（DTFBTEH） were compouned, then reacted with the electro-donating monomer BDTSn-TTBO, two polymers, namely PBDT-TTBO-DTBTEH and PBDT-TTBO-DTFBTEH were synthesized, respectively. The resulted copolymer PBDT-TTBO-DTBTEH showed the optical band gap of approximately 1.58 eV, EHOMO and ELOMO of-5.45 eV and-3.80 eV. The device was prepared by using PBDT-TTBO-DTBTEH as donor material and PC₆₁ BM as acceptor material, the highest PCE was 2.70%(V_OC = 0.77 V,J_SC = 6.62 mA/cm²,FF = 53.04%). By the contrast, the containing fluorine copolymer PBDT-TTBO-DTFBTEH exhibited the optical band gap of about 1.75 eV, EHOMO and ELOMO of-5.52 eV and-3.81 eV. And the device was finished by using PBDT-TTBO-DTFBTEH as donor material and PC₆₁ BM as acceptor material, the highest PCE was 2.81%(V_OC = 0.82 V,J_SC = 6.28 mA/cm²,FF =54.52 %).3. Chapter 4, By Stille coupling, BDTSn-TTBO reacted with 4,6-dibromo-2-（2-hexyldecylsulfonyl）-thieno[3,4-b]thiophen（TTS） and 2,5-2-hexyldecyl-1,4-dioxygen-3,6-bis（5-bromothiophene）-pyrrole[3,4-c]pyrrole（DPP） respectively, then got two polymers PBDT-TTBO-TTS and PBDT-TTBO-DPP. The polymers had good thermal stability and solubility. The optical band gap of PBDT-TTBO-TTS and PBDT-TTBO-DPP were about 1.66 eV and 1.46 eV, EHOMO of-5.35 eV and-5.38 eV, ELOMO of-3.87 eV and-3.92 eV. The device was prepared by using PBDT-TTBO-TTS as donor material and PC₆₁ BM as acceptor material, the highest PCE was 1.07%(J_SC = 3.45 mA/cm², V_OC =0.95 V, FF =32.61 %).