| Organic solar cells(OSCs)have been focused and widely studyed due to their outstanding advantages of low-cost,light-weight,flexibility and so on in the past few years.More and more organic conjugated units have been applied to construct organic photovoltaic electron-donating materials.Their power conversion efficiencies(PCEs)have been continously improved for these OSCs by adjusting the enery levels and absorption spectra of the electron-donating(D)and electron-accepting(A)materials in the active layer,which make their enery levels and absorption spectra matched.This dissertation summarizes their developing progress and working principle of OSCs,as well as the high-efficiency electron-donating materials based on benzo [1,2-b:4,5-b?]dithiophene(BDT)unit.Several D-A type small molecules(SMs)and polymers based on the BDT and benzodi(pyridothiophene)(BDPT)units were designed and synthesized as electron-donating materials.Their photophysical and electrochemical properties,as well as photovoltaic performance in bulk-heterojunction organic solar cells(BHJ-OSCs)were investigated.As a result,the relationships among structures of these donor materials and PCEs of their photovoltaic devices were revealed.The research results are summarized as follows.1.Two-dimensional A-D-A type small molecules of BDTx-2TVTDPP and BDTy-2TVTDPP containing the BDT and diketopyrrolopyrrole(DPP)units were syn-thesized used as electron-donating materials.The influence of its substituted position of the BDT unit in the molecular framework on thermal stability,electrochemistry and photovoltaic properties were further investigated.As a result,the BDTx-2TVTDPP based on 2,6-substituted BDT unit exhibits better crystallinity and narrower optical bandgap(1.61 eV).The BDTy-2TVTDPP based on 4,8-substituted BDT unit shows a lower HOMO energy level(-5.53 eV)and stronger photoresponse.As a result,the BHJ-OSCs based on the BDTy-2TVTDPP/PC71 BM blend films exhibit better photovoltaic performances with a PCE of 2.85%,an open-circuit voltage(Voc)of 0.86 V,a short-circuit current density(Jsc)of 8.6 mA/cm2.2.Two D-A type conjugated polymers based on the BDPT electron-donating unit and an electron-deficient unit of DPP(or quinoxaline(Qx))were designed and synthesized.The influence of these electron-withdrawing units of DPP and Qx on thermal stability,absorption spectrum,electrochemical and photovoltaic properties was also investigated.The results show that,the hole mobility of PBDPT-Qx is 3.20 × 10-4 cm2V-1S-1,which is one order of magnitude higher than that of PBDPT-DPP(1.48 × 10-5 cm2V-1S-1).PBDPT-QX exhibits a lower HOMO energy level of-5.52 eV and stronger photo-response than PBDPT-DPP.The BHJ-OSCs based on the PBDPTQx/PC71 BM blend films display better photovoltaic performances than those ones based on the PBDPT-DPP/PC71 BM blend films,in which the former devices displayed a PCE of 3.91% with a Voc of 0.86 V,a Jsc of 8.86 mA/cm2 and a filled foctor(FF)of 50.98%.3.Two conjugated polymers of PP7 and PP8 based on 8-phenyl substituted BDT and benzo[1,2-c:4,5-c']dithiophene-4,8-dione(BDD)units were synthesized.The effect of the appending 2-ethylhexyloxy numbers in the side chain on thermal stability,absorption spectrum,electrochemical and photovoltaic performances was studied.The results indicate that the stacking orientations of the PP7 and PP8 blend films in active layer are respectively the edge-on and face-on types,in which the latter type is benificial to transport free charge and promote its photovoltaic performance.As a result,the PP8/PC71 BM and PP8/ITIC based OSCs exhibit an improved PCE of 8.50% and 9.01%,respectively.A Voc of 0.90 V,a Jsc of 16.69 mA/cm2 and a FF of 60.0% are observed in the PP8/ITIC based OSCs at the same time. |
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