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Title 2D Materials and their application in Ternary Organic Photovoltaic Devices
Author Τζουρμπάκης, Παύλος
Abstract The scope of this diploma thesis is to examine the addition of a 2D material, Tungsten Disulfide (WS2) with and without gold nanoparticles (Au NPs),into the active layer (AL) of an Organic bulk-heterojunction (BHJ) Photovoltaic (OPV) device. Relatively, narrow spectral overlap of organic polymer absorption bands within the solar spectrum and morphology are two of the major limitations of organic solar cells. Among different strategies that are in progress to tackle this restriction, the novel concept of Ternary OPV is a promising strategy to extend the absorption spectra of large bandgap polymers to the near IR region and to enhance light harvesting in single bulk-heterojunction solar cells. By using the laser ablation method, Au NPs are formed into liquids with pico- and femto-second laser pulses and be implanted with WS2 nanosheets (NS). It is found that the laser induced anchoring of Au NPs onto NS basal plane and edges resulted in enhanced light harvesting that is potentially useful for energy conversion and storage applications. Due to the perfect energy level matching of WS2 and the polymer blend, excitons can be efficient dissociate at the interfaces of Donor (low electron affinity)-Acceptor (high electron affinity) and thus electrons can be efficiently transported to the negative Aluminum electrode. Enhancement of the efficiency of bulk heterojunction (BHJ) Polymer-Fullerene devices is demonstrated first by the addition of WS2 and then WS2-Au NPs solutions in the active layer of the devices. The power conversion efficiency (PCE) of the binary device consisting of a poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'- benzothiadiazole)] (PCDTBT) : [6,6]-phenyl-C71-butyric-acid methyl-ester (PC71BM) blend as the donor-acceptor pair was 5.6%. A significant enhancement of 8% was achieved reaching 6.1% after the employment of WS2NS (PCDTBT:WS2:PC71BM), while the incorporation of Au NPs decorated WS2NS (PCDTBT:WS2–Au NPs:PC71BM) further improved by 12.5% the Power Convention Efficiency (PCE), reaching 6.3%.The efficiency enhancement can be attributed to light scattering of the large diameter WS2 NS, improving the absorption spectra inside the photoactive layer and as well as to better charge transport properties of the ternary blend in the case of the undoped WS2 blend. On the other hand, the enhancement of performance of devices with Au NPs doped WS2 ternary blends, can be also attributed further increased absorption due to the effects of the phenomenon of Localized Surface Plasmon Resonance (L effects of the small diameter Au NPs.SPR)
Language Greek
Issue date 2015-11-20
Collection   Faculty/Department--Faculty of Sciences and Engineering--Department of Materials Science and Technology--Graduate theses
  Type of Work--Graduate theses
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