Novel Donor And Acceptor Photovoltaic Materials Of Polymer Solar Cells

Polymer solar cells(PSCs)possess the characteristics like solution processing,light weight,large-scale fabrication,flexibility and semitransparency,which have attracted extensive attentions.PSCs usually consist of the active layers,charge transfer layers and conducting electrodes.Among of them,the active layers influence the performance of PSCs directly.The active layer materials contain donor materials of P-type polymer semiconductor and acceptor materials of N-type organic semiconductor.Up to now,the most successful donor materials and acceptor materials are D-A type copolymers and A-D-A type small molecules,respectively.A-D-A type small molecules acceptor and D-A type copolymer donor materials are research highlights of PSCs due to the tunable energy levels and bandgaps,complementary spectral absorption and good compatibility.We make some attempts for the purpose of developing high performance small molecules acceptor materials based on ladder fused-units and D-A type copolymer donor materials based on fused benzothiadiazole unit.The research contents are as follows:(1)We can tune solubilities,optical bandgaps,energy levels and molecular stacking behaviors of A-D-A type nonfullerene acceptors by side-chains engineering.We synthesized five small molecule acceptors of NNFA[n,m]("n" and "m" stand for the number of alkyl carbon atoms in the in-plane and out-of-plane side chains),NNFA[0,6],NNFA[6,3],NNFA[6,6],NNFA[12,3]and NNFA[12,6],by changing n and m.Those small molecules include a nonacyclic ladder-fused donor unit and an acceptor unit of FIC.Then,we prepared polymer solar cells by blending NNFA[n,m]with a wide bandgap polymer donor(FTAZ).Ideal side-chain units improve the properties of acceptor materials and improve the solar cells performance.Among those solar cells,NNFA[6,6]and NNFA[12,3]with medium solubility(～100 mg mL)present suitable miscibility with FTAZ,and afford more favorable morphology and higher device performance than other NNFAs.Corresponding solar cells obtained the highest power conversion efficiency of 10.56%and 10.81%,respectively.(2)Carbon-oxygen-bridged ladder-type fused-ring units are ideal donor block units for A-D-A small molecule acceptor materials because of its great planarity and strong electron-donating capability.We designed and synthesized a small bandgap(1.24 eV)acceptor with a decacyclic carbon-oxygen-bridged donor unit COi10 and an acceptor unit DFIC.The wide and strong spectral absorption in visible and near infrared region board of acceptor materials benefit to obtain high short-circuit current.We prepared polymer solar cells basing on COiIODFIC as acceptor material and PTB7-Th as donor material.We got a highest PCE of 10.9%and a Jsc of 21.97 mA.cm 2 in PTB7-Th/COi10DFIC solar cells.(3)Acceptor units will influence the solubility,optical band gap,energy levels and molecular stacking behavior of A-D-A type small molecule acceptors.Here,we designed an acceptor unit of BTC based on benzothiophene unit.Then,we synthesized a medium-bandgap(1.65 eV)nonfullerene acceptor with a donor unit of C10-IDT and an acceptor unit of BTC.A larger conjugated plane of BTC benefit to obtain ideal blend film morphology,better molecular stacking and charge transfer.We prepared polymer solar cells basing on IBCT as acceptor material and L1 as donor material.We got a highest PCE of 11.26%and a VOC of 1.02 V in L1/IBCT solar cells.Tandem solar cells with L1/IBCT front cells offered a PCE of 15.25%and a Voc of 1.82 V.(4)Benzothiadiazole unit is an ideal acceptor unit for D-A copolymer donor materials due to its strong electron-withdrawing capabilities and good planarity.Fused-ring benzothiadiazole unit DTBT have better charge transfer ability due to its larger conjugated plane.We designed and synthesized a large bandgap D-A type copolymer donor of D18.We prepared polymer solar cells basing on Y6 as acceptor material and D18 as donor material.The best D18:Y6 cells gave a PCE of 18.22%,with a Voc of 0.859 V,a Jsc of 27.70 mA.cm-2 and a FF of 76.6%.APCE of 18.22%is the highest value for organic solar cells to date.