Synthesis And Photovoltaic Investigation Of Wide-bandgap Conjugated Polymers Based On Thienoacene

Rapid progress has been made in polymer solar cells?PSC?in the past few years,The state-of-the-art PSC have reached power conversion efficiencies?PCE?over 14%?To design high-performance photovoltaic polymers,the chemical structure has to be synchronized with processing parameter.In this paper,from the point of view of rigid conjugated polymer backbone and peripheral flexible side chain,we consider that the high-efficient conjugated polymer?CP?donor materials and the acceptor should meet the requirements of energy level matching,absorption spectrum complementary,and good aggregation and morphology of the blend film.A series of wide band gap?WBG?CPs has been synthesized by Stille coupling reaction,benzo[1,2-b:4,5-b']dithiophene?BDT?with good electron donating ability and high planarity was selected as electron donor,5,6-difluorobenzene[d][1,2,3]triazole?FBTA?and newly synthesized dithieno[2,3-d:2',3'-d']benzo[1,2-b:3,4-b':5,6-d'']trithiophene?DTBTT?as the electron-deficient unit,It is expected to improve the photovoltaic performance through fine side chain regulation and tuning polymer skeleton?-conjugated planarity.In the chapters 2 and 3,the 2-alkylthio-3-alkylthiophenyl or bisalkylthiothiophene groups was introduced into the main chain of BDT as the first component,the electron-deficient unit FBTA was used as the second component and an alkylthiophenyl substituted BDT unit as the third component.The 2-alkylthio-3-alkyl substituted polymers PBDT-AST45,PBDT-AST55,PBDT-AST65 and PBDT-AST;bisalkylthiothiophene substituted polymers PBDT-DST45,PBDT-DST55,PBDT-DST65 and PBDT-DST were synthesized by controlling the ratio of the three monomers in the two systems.The comprehensive comparison shows that the introduction of pendant alkylthio group can deepen the highest occupied molecular orbital energy level(E_HOMO),so as to increase the open circuit voltage?Voc?,and the devices based on PBDT-AST65/ITIC and PBDT-DST55/ITIC achieve the highest Voc?0.98 V?,which is increased by6%?0.92⁰.98V?higher than PBDT-T/ITIC based device.Meanwhile,the introduction of the alkylthio group has improved the?-?stacking property of the polymer skeleton,thereby forming a more ordered structure between the skeleton and the side chain,and improving the charge transport performance.The PBDT-AST65/ITIC based device showed the best performance(V_OC=0.98 V,J_SC=12.38 mA cm^-2,FF=47.80%,PCE=5.76%).It can be seen that the introduction of an alkylthio group into the polymer is beneficial for increasing the PCE of the WBG donor material.In the fourth chapter,the DTBTT unit was synthesized by extending the?-conjugated system of benzo[1,2-b:3,4-b':5,6-d'']trithiophene?BTT?unit.For investigating the effect of extending conjugation,two wide band gap benzo[1,2-b:4,5-b?]dithiophene?BDT?-based conjugated polymers?CPs?,PBDT-DTBTT and PBDT-BTT,which were coupled between alkylthienyl-substituted benzo[1,2-b:4,5-b?]dithiophene bistin?BDT-TSn?and the dibromides DTBTTBr₂ and BTTBr₂ bearing alkylacyl group,were prepared.The comparison result revealed that the extending of conjugated length and enlarging of conjugated planarity in DTBTT unit endowed the polymer with a wider and stronger absorption,more ordered molecular structure,more planar and larger molecular configuration and thus higher hole mobility.The best photovoltaic devices exhibited that PBDT-DTBTT/PC₇₁BM showed the power conversion efficiency?PCE?of 2.73%with an open-circuit voltage(V_OC)of 0.82 V,short-circuit current density(J_SC)of 6.29 mA cm^–2 and fill factor?FF?of 52.45%,whereas control PBDT-BTT/PC₇₁BM exhibited a PCE of 1.98%under the same experimental conditions.The 38%enhanced PCE was mainly benefited from improved absorption and enhanced hole mobility after the conjugated system was extended from BTT to DTBTT.Therefore,this proves that extending the?-conjugated system of donor polymer backbone was an effective strategy of tuning optical electronic property and promoting the photovoltaic property in design of wide-bandgap?WBG?donor materials.