| The active layer material is the core of the polymer solar cell device,and its performance optimization and improvement is of great significance to improve the efficiency of the solar cell device.In this paper,we expect that the excellent photoelectric performance of an organic solar cell device can be obtained by the optimization of the design of the donor material in the active layer.In this paper,we design a new donor units of the active layer DTBDT-TS.The donor units DTBDT-TS are reacted with partial acceptor units(2,1,3-benzothiadiazole,5,6-difluoro-2,1,3-benzothiadiazole,naphtho[1,2-c:5,6-c’]bis[1,2,5]-thiadiazole,thiophene isoindigo and its derivatives).A series of narrow band gap D-A type copolymers are synthesized by Stille coupling reaction,and the thermal stability,absorption spectrum and electrochemical properties of the polymer are characterized,the dihedral angles and molecular energy levels of the polymer are calculated and the photovoltaic properties of the polymer are studied.Firstly,the alkylthio thiophene side chains are introduced into DTBDT unit,and the electron donor unit is prepared: DTBDT-TS.The narrow band gap conjugate polymers PDTBDT-TS-DTBT and PDTBDT-TS-DTFBT are obtained by Stille coupling,with the electron donor unit DTBDT-TS,the BT and FBT as the electron acceptor unit respectively,2-butyloctylthiophene as conjugated π bridges.The results show that the conjugated polymers PDTBDT-TS-DTBT and PDTBDT-TS-DTFBT have sunlight absorption rangingfrom 300 to800 nm,the optical bandgap is 1.67 and 1.68 eV,LUMO level is-3.55 and-3.71 eV respectively,HOMO level is-5.22 and-5.54 eV,respectively.However,photovoltaic properties of the two polymers can not characterized because of the poor solubility,which seriously affected the film forming processability.To improve solution processing performance,2-octyldodecyl is introduced to the electron acceptor unit by optimizing the design of the monomer,the polymer PDTBDT-TS-DTBT2 and PDTBDT-TS-DTFBT2 are successfully synthesized,and the thermal stability of these new polymers is not reduced,the optical band gap is increased and the level is kept constant.The PSCs device structure is ITO/PFN/Polymer:PC61BM/MoO3/Ag.Polymer photoelectric conversion active layer based on PDTBDT-TS-DTBT2:PC61BM = 1:1.5 blending film,while adding 3% DIO,the device photoelectric conversion efficiency(PCE)is up to 3.47%(VOC = 0.81 V,JSC = 6.53 mA/cm2,FF = 65.69%),the PCE based on PDTBDT-TS-DTFBT2: PC61 BM = 1: 1.5 blending film photoelectric conversion efficiency of the device is up to 4.61%(VOC = 0.88 V,JSC = 9.27mA/cm2,FF = 56.48%).Fluoride-substituted polymers have more excellent photovoltaic properties and better molecular planarity,facilitating carrier transport,resulting in higher short-circuit current and energy conversion efficiency ultimately.Secondly,the polymer PDTBDT-TS-DTNTHD is obtained by Stille coupling reaction with the donor unit DTBDT-TS and the acceptor unit DTNTHD.It has good film-forming processability,the thermal decomposition temperature is 347 ℃,The absorption ranges from300 to 800 nm,and the optical band gap is 1.67 eV.HOMO and LOMO were-5.35 and-3.68 eV,respectively.The PCE is obtained up to 2.03% of the device prepared with PDTBDT-TS-DTNTHD: PC61 BM as the active layer(VOC = 0.78 V,JSC = 6.80 mA/cm2,FF =38.3%).Thirdly,the donor unit DTBDT-TS and the receptor unit TIID are subjected to Stille coupling reaction to obtain the polymer PDTBDT-TS-TIID,and the UV-absorbing properties,electrochemical properties and thermal stability of the polymer were studied.The results show that the polymer has good film forming process,and the thermal decomposition temperature is 344℃.It has strong absorption in the visible region,absorption range extends from 300 to 1000 nm,and the optical band gap is only 1.28 eV,the HOMO and LUMO levels are-5.28 eV and-4.00 eV respectively.The PCE Is obtained up to 0.66% of the device prepared with PDTBDT-TS-TIID:PC61BM as the active layer(VOC = 0.47 V,JSC = 3.13mA/cm2,FF = 44.84%). |
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