The Photovoltaic Performance Of Narrow Bandgap Block Copolymer

Recently,the power conversion efficiency of all-polymer organic solar cells has been improved with the emergence of narrow bandgap polymerized small molecule acceptors(PSMAs).Nevertheless,there are still many difficulties in the further development of blend heterojunction organic solar cells,especially the regulation of phase separation.Single-component organic solar cells with simplified device fabrication and stable morphology,can provide effective ways to solve the above problems.However,the current efficiency of single-component organic solar cells still lags far behind that of allpolymer organic solar cells,which requires further research on materials and devices.Based on this,the main contents carry out the followings:In the first part,two narrow-bandgap block conjugated copolymers with a(D1-A1)(D2-A2)backbone architecture,namely PBDB-T-b-PIDIC2T and PBDB-T-b-PTY6,are designed and synthesized for single-component organic solar cells(SCOSCs).Compared to all previously reported materials for SCOSCs,PBDB-T-b-PIDIC2T and PBDB-T-bPTY6 exhibit narrower bandgap(1.55 and 1.43 eV,respectively)for better light harvesting.When incorporated into SCOSCs,the short-circuit current density(Jsc)is significantly improved to over 15 mA cm-2,together with a record-high power conversion efficiency(PCE)of 8.64%.Moreover,these block copolymers exhibit low energy loss due to high charge transfer(CT)states(Ect)plus small non-radiative loss(0.26 eV),and improved thermal stability.The close structural relationship between block polymers and their binary counterparts also provides an excellent framework to explore further molecular features that impact the photovoltaic performance and boost the state-of-theart efficiency of SCOSCs.Furthermore,due to the terminal group in Y6 based nonfullerene acceptor is often consist of a mixture of two isomers which have similar polarity,and is very difficult to separate.Regioselectivity controlled PBDB-T-b-PTY6-γ is successfully synthesized.This further creates the challenge for uncertain reaction sites during polymerization.Previous reports have demonstrated the regularity of polymer backbone has an impact on the molecular packing,energy disorder as well as synthetic repeatability,eventually the enhancement of device performance.In specific,we designed and synthesized a block copolymer PBDB-T-b-PTY6-γ by polymerizing regular polymer PTY6 on one side and p-type donor polymer PBDB-T on the other side.The regioselectivity control endows PBDB-T-b-PTY6-γ with extended absorption,more tight backbone packing,outperforming a higher short-circuit current density(Jsc)exceeding 19 mA cm-2 together with the best PCE of 10.51%,indicating the importance of structural regularity in the block copolymer for achieving efficient SCOSCs.SCOSCs can reduce procedures for preparing ready-to-coat organic conductive ink and photoactive layer,as well as remarkably stable film morphology,which have proven to be a viable alternative to the bulk-heterojunction system.However,the state-of-the-art PCE of single-component organic solar cells still lags significantly behind binary heterojunction solar cells.In this thesis,we successfully synthesized a series of block copolymers and explored their application in SCOSCs,our systematical study may provide an effective approach to realizing high-efficiency SCOSCs.