Synthesis And Photovoltaic Property Of D-A-type Conjugated Polymers Based On Benzodithiophene And Functionlized Quinoxaline Units

Polymer solar cells?PSCs?have been widely concerned and studied by scientists due to their advantages of light weight,simple preparation,solution processing,and flexibility to fabricate large-area devices.This dissertation briefly introduces the research progress of quinoxaline?Qx?copolymer donor materials.For the shortage of high-efficiency organic polymer donor materials and lack of design theory guidance for designing high-performance molecules,three series of novel and high-performance copolymer donor materials based on alkylthio side-chains engineering benzodithiophene?BDTTS?and various side-chains engineering quinoxaline?Qx?derivatives had been designed and synthesized.Their structure of the target molecules and copolymers were characterized by ¹H NMR,¹³C NMR and time of flight mass spectrometry?MS?.The opto-physical properties,electrochemical and thermal properties of these copolymers have also been investigated by UV-Vis,PL,CV,TGA and DSC.Moreover,non-fullerene?NF?PSCs were also fabricated to investigate the photovoltaic properties of these materials,and some excellent-performance of copolymer donor materials were obtained.The relationship between the molecular structure of the material and its photovoltaic performance was also revealed systematically.The research content and results of this thesis are as follows:?1?Two novel D-A type copolymer,namely PBDTTS-IQ and PBDTTS-2FIQ,based on BDTTS as donor unit,non-fluorinated or fluorinated indo[2,3-b]quinoxaline?IQ or 2FIQ?units as acceptor unit,were designed and synthesized,respectively.Their influence of different IQ on the optoelectronic properties of resulting copolymers were also investigated.Compared with the PBDTTS-IQ,the PBDTTS-2FIQ exhibits a lower HOMO energy level?-5.30 e V?,better planarity,and higher charge mobility(3.94×10^-4cm²V^-1s^-1)and hole mobility(5.83×10^-4cm²V^-1s^-1).As result,PSCs based on PBDTTS-2FIQ:PC₇₁BM obtained a power conversion efficiency?PCE?of 7.40%with an open-circuit voltage(V_oc)of 0.84 V,a short-circuit current density(J_sc)of 13.26 m Acm^-2and a fill factor?FF?of 66.0%,while PBDTTS-IQ based PSCs only achieved a PCE of 4.96%.The study shows that combining the fused ring strategy and the fluorination strategy can increase the charge mobility and hole-mobility of the corresponding copolymer,thereby improving the PCE of the corresponding device.?2?Two novel D-A copolymers,namely PBDTTS-DTCl Qx and PBDTTS-DTCl SQx,based on BDTTS as donor unit,chlorine atom and alkyl?or alkylthio?thiophene side-chain engineer quinoxaline?Qx?,were designed and synthesized.The influence of various side-chainsat Qx on the optoelectronic properties of resulting copolymers werealso studied.The study found that the introduction of the alkylthio chain in the conjugated side chain of the copolymeric system only played a positive role in lowering the HOMO energy level,whereas a negative role in elevating carrier mobility and molecular stacking property.As results,based on PSC of PBDTS-DTCl SQx:Y6 exhibited a PCE of 13.58%with V_ocof 0.81 V,J_scof 24.5 m A cm^-2and FF of 68.24%.Encouragingly,an outstandingly improved PCE of 14.28%with an enhancement of 5%was achieved in PBDTS-DTCl Qx:Y6based device due to an increased J_scof 25.9 m A cm^-2,which is one of the highest reported efficiencies for PSCs based on BDT-Qx copolymers to date.This study demonstrates that optimizing the conjugated side chains of Qx based copolymers is an efficient tactic to improve photovoltaic properties.?3?Two novel narrow bandgap D-A type copolymers,namely PBDTTS-2FQx BA and PBDTTS-2FQx TA,based on BDTTS as donor group,phenyl ester alkyl-chains and thiophene ester alkyl-chains engineering Qx,were synthesized and employed as the photovoltaic donor materials for NFPSCs.The resulting copolymer PBDTTS-2FQx TA exhibits a red-shifted absorption,but PBDTTS-2FQx BA presents a stronger light response and higher hole-mobility(3.20×10^-4cm²V^-1s^-1)in comparison with PBDTTS-2FQx TA.As results,the PSC based on PBDTTS-2FQx BA:Y6 exhibited a PCE of 13.34%with V_ocof 0.81 V,J_scof 24.7 m A/cm²and FF of 68.24%,while PBDTTS-2FQx TA presents only a PCE of 11.6%.These results demonstrate that the phenyl ester alkyl-chainengineering Qx-based copolymer is a simple and effective strategy to design high-performance conjugated copolymer photovoltaic materials.