Systhesis And Performance Of D-A Type Conjugated Polymer Photovoltaic Materials And Device Optimization Study

In this dissertation,the basic structure and operational principle of polymer solar cells(PSCs)have been introduced in brief.The recent developments of polymer donor materials in fullerene-based PSCs(F-PSCs)and polymer acceptor materials in nonfullerene-based PSCs(NF-PSCs)have been emphatically reviewed.In bulk heterojunction PSCs(BHJ-PSCs),the solubility,absorption ability,molecular energy levels and molecular regularity of the photoactive materials,morphology and charge transfer ability of the blend film and device structure of the solar cells have a great impact on the photovoltaic performance.To meet the various requirements mentioned above,we have designed and synthesized series of polymer donor materials based on benzodithiophene(BDT)and spiro[cyclopentadithiophene-4,9'-fluorene](STF)as well as some polymer acceptor materials based on naphthalene imide(NDI).The molecular structures of all the intermediates and target polymers were characterized and confirmed by nuclear magnetic resonance spectroscopy(NMR)and time-of-flight mass spectrometry(MALDI-TOF MS).Ultraviolet visible absorption spectroscopy(UV-Vis),cyclic voltammetry(CV),thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC)were applied to analyze the photophysical properties,electrochemical properties,thermal properties and crystalline properties of polymer materials,respectively.The morphology of the blend films was characterized by atomic force microscopy(AFM)and transmission electron microscopy(TEM).The photovoltaic properties of the F-PSCs based on polymer donor materials and all-PSCs based on polymer acceptor materials were investigated.Finally,the inverted device was employed to further optimize photovoltaic performance of some high efficient polymer photovoltaic materials.The main contents were summarized as below:1.A series of donor-acceptor(D-A)type terpolymers(ra-P1,re-P2 and re-P3)based on BDT and 1,4-diketopyrrolo-[3,4-c]-pyrroles(DPP)with 5,6-difluoro-4,7-bis(4-(2-ethylhexyl)thiophen-2-yl)benzothiadiazole(DTffBT)as the electron-withdrawing conjugation side chain were designed and synthesized.The effects of DTffBT contents and the regularity of molecular structure on the photophysical properties,electrochemical properties and photovoltaic properties of three terpolymers were investigated in detail.The results indicated that all three polymers showed a broad absorption spectrum(300-900 nm)and a low-lying HOMO energy level(<-5.3 eV).Two regular terpolymers re-P2 and re-P3 have stronger absorption ability,higher hole mobility and better morphology of the blend film as compared with the random terpolymer ra-P1.As a result,the power conversion efficiency(PCE)of BHJ-PSCs with ra-P1,re-P2 and re-P3 are 2.28%,3.30%and 4.08%,respectively.2.Two new medium-bandgap(MBG)D-A conjugated polymers(PSTF and PDTS)with fluorobenzotriazole(FBTA)as A unit,spiro[cyclopenta[1,2-b:5,4-b']dithiophene-4,9'-fluorene]or dithienosilole(DTS)as D unit,are designed and synthesized as polymer donor materials for applications in PSCs.The effect of spiro donor unit(STF)and planar donor unit(DTS)on molecular structures,photophysical,electrochemical and photovoltaic properties were investigated.The results showed that both copolymers are typical MBG polymers with a similar optical bandgap about of 1.83 eV.PSTF shows a broader absorption spectrum and a lower-lying HOMO energy level(-5.39 eV)relative to PDTS.Photovoltaic properties of the F-PSCs demonstrate that either PSTF or PDTS using PC61BM as acceptor exhibits better photovoltaic performances than that of ITIC as acceptor.Moreover,the PCE values of the PSCs based on PSTF are higher than the corresponding values of PDTS both the F-PSCs and the NF-PSCs system,reaching 3.66%and 2.42%,respectively.3.A new polymer acceptor material PNVT-6 based on NDI and di(2-disthienyl)ethylene was designed and synthesized.The aim is to improve the crystallinity of the polymer by reducing the alkyl chain length attached on NDI unit,which can increase the ?-? stacking of the polymer backbone and thus enhancing electron transport ability.All-PSCs based on P2-P5 as donor materials and PNVT-6 as acceptor material achieved a maximum PCE of 0.88%.4.Two polymer acceptor materials PNOZ and PNTZ based on NDI-oxadiazole and NDI-thiadiazole were designed and synthesized.Thermal properties,photophysical and electrochemical properties of polymer materials were investigated.Results demonstrated that both of the two polymers possess a broad absorption spectrum and well-matched HOMO and LUMO energy levels with donor polymer PTB7.All-PSCs with PTB7 as donor material,PNTZ exhibited a higher PCE of 2.58%compared to PNOZ.5.In view of the defects of unmatched absorption between donor and acceptor and relatively low hole mobility of the photoactive materials in the above-mentioned Part 4,PTB7-Th was chosen to replace PTB7 as a donor material due to its relatively broader absorption spectrum and higher hole mobility.All-PSCs based on PNTZ were fabricated and photovoltaic properties were optimized by utilization of interfacial modification material,additive and thermal annealing,and as a result a PCE up to 4.25%was obtained.6.Considering the advantages of inverted device,inverted PSCs with PTB7-Th as donor and PC71BM as acceptor were prepared and fabricated conditions were optimized.The photovoltaic performance of some F-PSCs and NF-PSCs with inverted structure were investigated,and the highest PCE of 10.07%was finally achieved.