Fabrication And Optoelectronic Properties Of The Polythiophene Derivatives/Graphene Based Nanocomposites

The third order nonlinear optical(non-linear optics, NLO) performance of conjugated polymers(conjugated polymer, CP), such as polythiophene derivatives, is widely studied. This is due to the CPs having ultra fast response time, high optical damage threshold, large nonlinear susceptibility, low dielectric constant and also, the CPs are easy to be processed. Due to the quantum Hall effect, high carrier mobility at room temperature, a large specific surface area, good optical transparency and excellent thermal conductivity, graphene has been studied extensively in the photovoltaic field and shows a potential application in the fields of high-speed optical communication, optical switch, optical limiting and so on. Nano semiconductor materials are also widely used in the photoelectric field.To combine the advantages of the above material, a series of poly(3-hexylthiophene)(P3HT) polymer nanocomposites were synthesized and the NLO properties of materials were studied.(1) Graphene oxide(GO) was synthesized by improved Hummer method. Reduction of graphene oxide(RGO) was prepared by hot alkali method and hydrazine hydrate reduction method, respectively. Results show that, the UV absorption of RGO shows a red shift compared to GO. The higher reduction degree of RGO, the higher thermal stability of RGO. The NLO absorption of RGO is similar to the GO i.e. it shows a saturated absorption(SA) at low incident energy while shows a reverse saturable absorption(RAS) at high energies. Moreover, the higher reduction degree of RGO, the better SA properties.(2) The intermediate products, graphene oxide-3-thiophene carboxylic ester(GOT) was synthesized using 3-thiophene carboxylic acid and GO acyl chloride(GO-Cl) as materials. Then, poly(3- hexylthiophene) grafted GO(P3HT-g-GO) composite was synthesized in situ using FeCl3 as oxidant. Results show that, the thermal stability of P3 HT is enhanced by GO. P3HT-g-GO has a good photoinduced electron transfer(PET) and NLO performance. Compared to pure P3 HT, NLO absorption coefficient(β) of P3HT-g-GO is 18cm/GW, increasing by 80% compared to P3 HT. the β value of P3HT-g-GO/PMMA film is-91cm/GW, which is 4.13 times than that of P3HT/PMMA(-22cm/GW) film.(3) P3HT-g-GO/CdS nanocomposites were prepared by in situ method, in which the size of CdS particles are 5-10 nm and show a good dispersion. The thermal stability of composite was enhanced by CdS, while the initial oxidation potential of P3HT-g-GO/CdS was reduced(0.75 eV of P3 HT, 0.68 eV of P3HT-g-GO/CdS). Meanwhile, the composite material has good NLO properties because the β value of the composite material is 32cm/GW in THF solution, which increased by 78% compared to P3HT-g-GO. The β value of P3HT-g-GO/CdS/PMMA films is-96cm/GW.(4) P3HT-g-GO/PbS nanocomposites were prepared in situ. The size of PbS particles is about 10-20 nm. P3HT-g-GO/PbS has a good electron/hole separation efficiency, a larger initial oxidation potential(0.78eV) and good NLO properties.The β value of the composite is 26cm/GW, increased by 44% compared to P3HT-g-GO(18cm/GW). The β value of P3HT-g-GO/PbS/PMMA films decreases to-54cm/GW.The different β value of P3HT-g-GO/CdS and P3HT-g-GO/PbS nanocomposites is speculated that they have different energy level. The matching energy level is good for enhancing β value of materials. Therefore, through designing the matching energy level structure between polymer and graphene or doping nanoparticles, for improving the NLO properties of materials,which has potential application value in the field of optoelectronics.