Synthesis And Photoelectric Properties Of R·Radical Polymers

Due to the special one-electron structure,organic free radicals are featured with high reactivity.With the rapid development of organic free radicals and the resolution of the stability problem,many stable free radical materials have been exploited and widely utilized.As a kind of organic semiconductor polymer material,the Galvinoxyls radical or2,2,6,6-tetramethyl piperidine-1-oxyl（TEMPO）radical has a promising application prospect in photoelectric conversion devices due to its excellent oxygen stability and redox properties.Nevertheless,at present,the researches on the application of free radical materials in polymer solar cells are insufficient.Moreover,the mechanism of action still remains unknown.Therefore,by synthesizing many new radical polymers and applying them to the photoactive layer or cathode interface layer of polymer solar cells,this study deeply investigated the effect of radical polymer addition on the performance of photovoltaic devices,which in turn provides a new opportunity to explore the mechanism of its action in photovoltaic devices.Inthesecondchapter,（4,8-bis（4,5-dioctylthiophen-2-yl）benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl）bis（trimeth-ylstannane）（BDT-TSn）and（4,8-bis（5-（2-ethylhexyl）-4-fluorothiophen-2-yl）benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl）bis（tr imethylstannane）（BDT-FSn）monomerswerepolymerizedwith2,6-di-tert-butyl-4-（（3,5-di-tert-butyl-4-hydroxyphenyl）（3,5-dibromophenyl）methylen-e）cyclo hexa-2,5-dienone（Gxl-H-Br）into conjugated polymers PHW-H and FEH-Gxl-H by Stille coupling reaction.Subsequently,conjugated polymers PHW and FEH-Gxl containing Galvinoxyls radical were gained by oxidation reaction.The free radical polymers PHW and FEH-Gxl were tested by gel permeation chromatography,electron param-magnetic resonance,thermal stability and UV-visible absorption spectrum.As demonstrated by the results,two conjugated free radical polymers containing Galvinoxyls radical were successfully synthesized.Then,the free radical polymers PHW and FEH-Gxl were applied as additives to the photovoltaic devices with the active layer of the bulk heterojunction in PBDB-T:ITIC system,respectively.When 0.5%PHW or 1%FEH-Gxl was added to the active layer as an additive,the power conversion efficiency（PCE）was increased from 8.73%to 9.63%and9.55%,the Open-circuit voltage(V_OC)was increased from 0.899 V to 0.901 V and0.903 V,the Short-circuit current(J_SC)was increased from 14.60 m A/cm² to 15.45 m A/cm² and 15.76m A/cm²,and the Fill factor（FF）was increased from 66.57%to 69.13%and 67.14%.It was speculated that the addition of Galvinoxyls radical may repress the triplet charge transfer of the PBDB-T:ITIC system,which resulted in the improvement of the exciton dissociation rate of the photovoltaic device and the inhibition of bimolecular recombination,thereby improving the PCE of photovoltaic devices.In the third chapter,the conjugated polymer FEH-BTMP with side groups containing TEMPO radical was prepared by Stille coupling reaction.The free radical polymer FEH-BTMP was detected by gel permeation chromatography,electron param-magnetic resonance,thermal stability and UV-visible absorption spectrum,confirming the successful preparation of conjugated radical polymers containing TEMPO.FEH-BTMP was then applied as an additive to the photovoltaic devices with the active layer of the bulk heterojunction in PBDB-T:ITIC system.When FEH-BTMP with a mass ratio of 1%was added,the PCE of photovoltaic devices was increased from 8.48%to 8.95%,the V_OCwas increased from 0.901V to 0.903 V,the J_SCwas increased from 14.15 m A/cm² to 14.62 m A/cm²,and the FF was increased from 66.56%to 67.81%.Through subsequent tests,the inhibitory effect of TEMPO radical on the triplet charge transfer of the PBDB-T:ITIC system was further verified.This inhibition in turn led to an increase in the exciton dissociation rate of the photovoltaic device and the inhibition of the bimolecular recombination,improving the PCE of the photovoltaic device.In the fourth chapter,alcohol-soluble ternary random conjugated polymer PDX-32 was prepared by Stille coupling reaction.The success of the alcohol-soluble conjugated free-radical polymer PDX-32 containing Galvinoxyls radical was confirmed by the tests of gel permeation chromatography,electron paramagnetic resonance,thermal stability,UV-visible absorption spectrum,etc.Next,alcohol-soluble radical polymer PDX-32 with different mass concentrations was added to the PBDB-T:ITIC photovoltaic device as the cathode interface layer.When 0.5 mg/m L PDX-32 was utilized as the cathode interface layer,it was revealed that the PCE was increased from 5.65%to 8.24%,the V_OCwas increased from0.812 V to 0.900 V,the J_SCwas increased from 13.83 m A/cm² to 14.50 m A/cm²,and the FF was increased from 58.06%to 63.05%.It was demonstrated by further tests that the?-spin single electron in the Galvinoxyls radical can enhance the conductivity of the radical polymer PDX-32 in comparison with the common organic cathode interface material PBN.Due to its good electrical conductivity,when PDX-32 was applied to the cathode interface layer of PBDB-T:ITIC devices,the exciton dissociation rate of the photovoltaic device was improved,the bimolecular recombination was suppressed,and the PCE of photovoltaic device was improved.