Effects Of Liquid Crystals Small Moleculars-doped ZnO Nanocrystalline And PEDOT:PSS On The Performance Of Polymer Solar Cells

The organic-inorganic hybrid solar cell is promising because of the advantages resulting from two types of materials with flexibility, light weight, low-cost fabrication and large-area easy preparation from organic material, high electron mobility, excellent chemical and physical stability, high electron mobility, inorganic nanocrystals size tunability from the inorganic semiconductors. However, as the organic polymers has bad compatibility with inorganic nanocrystalline, which make the active layer morphology of the organic-inorganic hybrid solar cell was not well controlled and inorganic nanocrystals tend to aggragation in the organic polymer. In order to improve dispersibility of inorganic nanocrystals in the polymer matrix, the inorganic nanocrystals always are modified by organic ligands. In this paper, we applied the liquid-crystalline ligands for the surface modification of the inorganic nanocrystals. Liquid crystals (LCs) are self-assembled dynamic functional soft materials which possess both order and mobility at molecular, supramolecular and macroscopic levels. This ordered self-assembly of molecules can initiate many functions. We modified the inorganic nanocrystals with small liquid crystal molecules to control the morphology of the active layer and improve the orderly of the active layer in the organic-inorganic hybrid solar cell.In this dissertation, firstly, a novel liquid-crystalline molecule containing a cyano-biphenyl mesogenic pendant,4’-n-(6-mercaptohexyloxy)-4-cyanobiphenyl (6CNBP-SH), was rationally designed and synthesized. We modified zinc oxide nanoparticles (ZnO NPs) with6CNBP-SH. The dispersion of modified ZnO NPs (6CNBP-SH@ZnO) is greatly improved by the surface modification of6CNBP-SH ligands. And the modified ZnO NPs endow obvious mesoscopic behavior, Inorganic nanocrystalline ZnO have orderly microscopic morphology. The experimental results show that the dispersion of modified ZnO NPs (6CNBP-SH@ZnO) is greatly improved by the surface modification of6CNBP-SH ligands. The photoluminescence (PL) measurement shows that the ultra-violet emission of ZnO can be enhanced by the surface modification of6CNBP-SH ligands and annealing at liquid crystal state temperature of6CNBP-SH@ZnO (110℃). Meanwhile, defect-related emission of ZnO in6CNBP-SH@ZnO almost disappears. We attribute this observation to the energy transfer between the ZnO NPs and6CNBP-SH, surface passivation of the ZnO and formation of ZnO nano-dispersing structure induced by6CNBP-SH molecules. The anisotropic behavior of6CNBP-SH@ZnO is also investigated. The results indicated that the6CNBP-SH liquid-crystalline ligands could endow the6CNBP-SH@ZnO hybrid obvious mesoscopic behavior. In addition, the increased optical anisotropy of6CNBP-SH@ZnO is also observed upon thermal treatment at110℃.Subsequently, photovoltaic performance of the polymer solar cell (PSC) based on poly3-hexylthiophene (P3HT) as donor and [6,6]1-phenyl-C61-butyric acid methyl ester (PCBM) as acceptor was improved by using the poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) modification layer treated by ionic liquid crystals4’-(N, N, N-trimethyl ammonium bromide hexyloxy)-4-cyanobiphenyl (6CNBP-N). Ionic liquid crystals4’-(N, N, N-trimethyl ammonium bromide hexyloxy)-4-cyanobiphenyl (6CNBP-N)-doped PEDOT:PSS films were prepared by dissolving6CNBP-N in2-propanol and methanol solvent and mixing with PEDOT:PSS. And the optimized power conversion efficiency (PCE) of the PSC based on P3HT:PCBM with the6CNBP-N (1.0mg)-treated PEDOT:PSS modification layer reached4.3%, in comparison with a PCE of2.5%for the PSC with the PEDOT:PSS layer without the ionic liquid crystals treatment. The enhanced performance of the PSCs is attributed to optimized surface morphology and the orderly of ionic liquid crystals of the PEDOT:PSS layers treated by ionic liquid crystals. And the6CNBP-N (1.0mg)-modified PEDOT:PSS layer induced uniform nanoscale phase separation of the active layer in short annealing time. A best power conversion efficiency of3.2%was achieved from the6CNBP-N (1.0mg)-modified PEDOT:PSS layer was annealed at mesophase.