Study On Graphene Hybrid Materials And Their Applications In Polymer Solar Cells

Firstly, the thermal annealing effects on a novel low band-gap polymer and related polymer solar cells (PSCs) have been attentively investigated in this dissertation. Secondly, the synthetic methods of three graphene hybrid are introduced and the photoelectric properties and their applications on PSCs of these products are checked out and studied systematacially. Lastly, we introduced a method to improve the power conversion efficiency (PCE) of the PSCs by inserting a liquid crystal molecule thin layer.1. A novel low band-gap polymer as the donor in the PSCsA novel low band-gap polymer poly [(4,4-bis(2-ethyl)cyclopenta-[2,1-b:3,4-b’] dithiophene)-2,6-diyl-alt-(5-octylthieno[3,4-b]pyrrole-4,6-dione)-1,3-diyl](PCPDTTP D, P1) is used to replace P3HT as the donor material to blend with PCBM. The roles of the thermal annealing on the structure and properties of P1:PCBM films and the performances of the PSCs are investigated. The best performance is obtained in the device without annealing. The value of Jsc, Voc and FF is5.97mA/cm2,0.86V and39%respectively, resulting in the maximum PCE of2.01%. Hole and electron mobilities increase after heat treatment compared to those of devices without annealing. The values of Jsc of the cells decrease as a result of the unbalance enhancement in the charge conduction of the thermal annealed P1:PCBM layer. The energy level offset between the HOMO of P1and the LUMO of P3HT is1.3eV. Thus, a Voc as high as0.86V is obtained for this type of PSCs.2. Graphene hybrid as the acceptor in the PSCsGraphene-Zinc Oxide (G-ZnO) nanocomposites are prepared through hydro thermal approach and used as the electron acceptors in poly-(3-hexylthiophene)(P3HT)-based bulk heterojunction OSCs. The morphology, chemical composition, crystal structure and photoelectric properties of G-ZnO are investigated. The blended film which is a mixture of different weight ratio of P3HT and G-ZnO is applied as the active layer in the OSCs device. The PCE increases first and then decreases with the increase of G-ZnO content in the blended active layer. The best PCE of the device reaches to0.98%, and Voc of0.81V and Jsc of4.92mA/cm are obtained in the device with15wt%G-ZnO content (ratio to P3HT). The average crystallite size is distinctly calculated to be16.6nm in the films corresponding to15wt%G-ZnO ratio of P3HT content. This condition is favor for the diffusion and separation of the most excitons. The electron mobility reaches to1.32×10-5cm2V-1s-1in the15wt%G-ZnO blended film and the Rs reaches the lowest value, so the PCE is the maximum.3. Graphene hybrid as the hole transport layer (HTL) in the PSCsA Mo6+cation modified graphene oxide (GO) derivative of GO-Mo is synthesized by a low-temperature solution method to replace PEDOT:PSS which posesses a strong acidic nature. The composition, morphology, crystal structure, surface chemical states and Hall carrier properties are investigated systematically. The transmittance of the GO-Mo films exceeds90%at the range from400to800nm. The GO-Mo films present a p-type property with a Hall measurement and the carrier concentration is about～1013cm-3. The hole mobility of the GO-Mo film with0.1g Mo-precursor is10.8cm2V-1s-1. The best performance is obtained in the device with the HTL prepared from0.10g Mo-precursor in GO solution, which is comparable to that of using conventional PEDOT:PSS. The value of Jsc, Voc and FF is9.02mA/cm2,0.59V and49%, respectively, resulting in the maximum PCE of2.61%. The effect of the GO-Mo layer number on the device’s performance is also studied. When the layer number increases to3, the GO-Mo fragment may be enough to provide a continuous and complete interface and to form an effective charge transport pathway. Then, a great increase in the cell efficiency can be obtained.4. Graphene hybrid as the anode in the PSCsA simple and facile technique for the synthesis of ATO-graphene is proposed by using graphite oxide (GO) and ATO nanoparticles through a hydrothermal approach. The ATO/G films present good transmittance and electrical conductivity. The impact effects of different annealing temperature and atmospheres on the films are studied. The PSCs are fabricated when ATO/G is used as the anode. The transmittance of the ATO/G films exceeds92%at the range from300to800nm, but the sheet resistance is as high as MΩ. To decrease the sheet resistance, the transmittance is sacrificed. The properties of the films annealed in the air are better than that of the films annealed in Ar atmosphere. To further decrease the sheet resistance, a thin Au nanoparticle film is deposited on the surface of the ATO/G films by a magnetron sputtering system. The ATO/G films are used as the anode to fabricate the PSCs device with a structure as: ATO/G/Au/MoO3/P3HT:PCBM/Al, and the PCE reaches to1.85%.5. A liquid crystal molecule improvement the PCE of the PSCs A simple method to enhance PCE of OSCs is introduced by insertion of a discotic liquid crystalline molecule [2,3,6,7,10,11]-Hexabutoxytriphenylene (HAT4) between HTL and active layer (P3HT:PCBM). In order to further investigate how the HAT4improves the PCE of OSCs, three different p-type materials are deposited on the substrate as HTLs, including PEDOT:PSS, MoO3and NiO, respectively. Comparing with the devices without HAT4, PCE is increased by43%,43%and35%in the ones with HAT4for different HTL, respectively. The microscopic process during annealing, HAT4molecules distribute in the P3HT:PCBM blended layer changing from the discotic phase to a column phase after150℃annealing. Homeotropic alignment in columnar phases can provide a most efficient pathway for carriers along the columnar axis which is favorable for charge transport. HAT4molecules distribute in the active layer to improve the charge mobility as a result of the enhancement of Jsc. The thickness of the HAT4film takes an importance role in the performance of the cells.