| Emerging alternative photovoltaic technologies such as dye sensitized solar cells (DSSCs) and organic solar cells (OSCs) have recently gained much attention as well as maturity and are on the step of being commercialized. To date, bulk heterojunction hybrid solar cells containing inorganic nanoparticles and semiconducting polymers are still lagging behind in respect of device performance although they can combine combining the advantages of both types of materials: solution processability and high absorption of semiconducting polymers, high electron mobility, and good chemical stability of inorganic semiconductor nanocrystals. Among the various factors impacting the photovoltaic performance of bulk heterojunction hybrid solar cells, the nanoscale morphology or microstructure of the active layer in hybrid solar cells is critical to ensure the high devices performance.Liquid crystalline materials with powerful self-assembly abilities can form ordering liquid crystalline microstructure under its LC state. Utilizing the LC materials' excellent orientation abilities to control the morphology and D-A interfaces of active layers of bulk-heterojunction hybrid solar cells not only achieve the nanoscale phase separation of D-type and A-type materials, but also improve the microstructure ordering of nanocomposites in active layers, which can effectively facilitate the exciton separation, charges transferring and transportation, improve the photovoltaic performances of hybrid solar cells.In this dissertation, firstly, a novel electron-donor material, liquid-crystalline polythiophene containing a cyano-biphenyl mesogenic pendant, poly[3-(6-(4-cynaobiphenyloxy)-hexyl)thiophene](P3HbpT), was rationally designed and synthesized. The spontaneous orientation of cyano-biphenyl mesogen endowed the P3HbpT with a well ordered morphology and facilitated the homogeneous dispersion of ZnO nanoparticles in the composites. The P3HbpT/ZnO composite films exhibited red-shift absorption (12nm), the lower LUMO and more ordered domains after undergoing annealing at liquid crystal (LC) states temperature (175℃), which indicated that the spontaneous assembly behavior of the liquid-crystalline polythiophene could induce the ZnO nanoparticles to form nano-dispersing structure with highly oriented channel layers upon heating at liquid crystalline states. Furthermore, the hybrid bulk-heterojunction devices based on P3HbpT/ZnO active layer have been constructed. Without extensive optimization, the devices undergoing annealing at LC state yielded a Voc of0.83V and power conversion efficiency (PCE) of0.61%, showing a significantly increased Jsc and FF with respect to the un-annealed counterpart.Secondly, A new donor-acceptor type liquid-crystalline copolymer, poly[3-(6-(cyanobiphenyoxy)thiophene)-alt-4,7-(benzothiadiazole)], P3HbpT-BTD, via copolymerization of liquid-crystalline electron-donating thiophene units and electron-accepting benzothiadiazole (BTD) units was designed and synthesized successfully. The nanostructure and photoelectric properties of the copolymer under different thermal treatment conditions were systematically investigated. Studies of the relationship between the annealing conditions and the nanostructures of the copolymer revealed that the cyano-biphenyl mesogenic units could induce the copolymer chains into a well ordered lamella structure upon annealing at liquid crystalline states temperature. When the hybrid films of P3HbpT-BTD/ZnO NPs were annealed at the temperature below or above the mesophase temperature region, less ordered copolymer chains brought an undeveloped interpenetrating network and caused the large aggregation of ZnO NPs. Most strikingly, the hybrid film annealed at liquid-crystalline state temperature (180℃) achieved the well-dispersed and high orientated nanoscale assembled nanoparticles regions. The spontaneous self-organization of P3HbpT-BTD enhanced the crystallinity and orientation of the ZnO NPs. Therefore, the resulting nanoscale phase separation of the hybrid films leaded to well-ordering percolated networks. Hybrid bulk heterojunction photovoltaic devices based on copolymer P3HbpT-BTD and ZnO NPs were fabricated under different annealing treatment. A best power conversion efficiency of1.98%was achieved upon annealing at mesophase temperature (180℃). Lastly, Liquid crystalline ligand,4-(5-(1,2-dithiolan-3-yl)pentanoate)-4'-(hexyloxy)-terphenyl (HTph-S), were employed as the semiconducting interface modification material for the fabrication of ZnO nanoparticles/P3HT hybrid solar cells. The HTph-S has a dithiolane ring which can attach to the surface of ZnO nanoparticles and the terphenyl aromatic group with hexyloxy end chain, which should make the ZnO nanoparticles miscible with conjugated polymers. A best power conversion efficiency of1.23%was achieved under an AM1.5G (100mW cm-2) condition after thermal treatment at LC state temperature (120℃). The enhanced performance of hybrid solar cells may mainly be accounted for the improved compatibility, enhanced charge separation and transfer efficiency and optimized micro-morphology of the ZnO/P3HT hybrid films induced by the self-organizing behavior of HTph-S ligands in its LC state. |
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