Photo-electric Properties Of The New Type Transparent Conductive Electrodes Fabricated By Nanosphere Lithography

The transparent conductive electrodes (TCEs) were greatly developed due to the rapiddevelopment and industrialization of the display and optical communication technique since the1990s.Meanwhile, the more and higher standards were required for the TCEs. The indium tin oxide (ITO) waswidely used currently. However, such traditional ITO TCEs appears to be increasingly problematic with thedevelopment of modern photo-electric devices, which mainly due to the limited availability of the indiumand their intrinsic chemical and electrical drawbacks. On the other hand, ITO is brittle and often crackswhen bent due to its ceramic nature. Aimed to resolve such problems, other types of TCEs such as metalnanowires film, grapheme film and carbon nanotubes film were developed to replace the ITO TCEs.However, there was always a “tradeoff” between the conductivity and the transmittance for these TCEs.Fortunately, Ebbesen et al first reported the extraordinary optical transmission properties of noble metalnano-hole array films, which originated from the surface plasmonic resonance. And such phenomenagenerated a strong interest for the researchers. Such patterned metal nanostructures were expected toresolve the problems of traditional TCEs. Different fabrication methods including electron beamlithography (EBL), focused ion beam lithography (FIBL) and phase-shifting lithography (PSL) have beendeveloped for this goal. However, patterned metal nanostructures have been fabricated only with a finitearea by using the slow and expensive “top-down” fabrication methods mentioned above, which cannotmeet the requirement in the practical applications. The nanosphere lithography technique provided us aneffective means for the inexpensive and large-scale fabrication of nano-pattern, which was used to fabricateall kinds of patterned nanostructures.Aimed to resolve the problems for the using of plasmon resonance absorption enhancement inthin film solar cells and based on the research of the TCEs, large-scale patterned metal nanostructures werefabricated using the versatile nanosphere lithography technique. Based on the understanding of their opticaland electrical properties, we tried to use such new type TCEs as a SPR component directly. Our resultsshowed that the periodically patterned metal film had a high transmittance, which closely related to thesurface plasmonic resonance (SPR) effects. In addition, such patterned metal nanostructure had a perfect conductivity. Such new type TCEs can serve as a transparent conductive electrode while possess the role assurface plasmonic resonance component make it very attractive, which will find potential photo-electricdevices applications in a range from plasmon-enhanced broadband photovoltaics to SPR-based chemo-andbiosensors. The paper mainly includes three parts such as follows:(1) The large-scale fabrication of gold network electrodes and its refractive index sensing properties:Large-scale gold network electrodes with perfect optical properties were fabricated using the versatileNSL technique combined with the reactive ion beam etching (RIE). Such patterned gold networks arrayhad a refractive index sensing property. The transmission peak of the new type TCEs red-shifted inresponse to solutions with the increased refractive index. A sensitivity of161nm/RIU (refractive indexunit) was obtained in the visible region, which exhibited great promise for the refractive index sensingapplication.(2) The influences of PS diameter, etching time and the film thickness on the conductivity andtransmittance: By changing the diameter of PS sphere, RIE etching time and thickness of the goldfilm, we investigated their influences on the morphology, optical and electrical properties of our newtype TCEs. Our results showed that the SPR peak blue-shifted with the increasing of etching time andfilm thickness. The SPR peak red-shifted for the larger PS diameter (600nm). The gold networkelectrode had higher conductivity than that of commercial indium tin oxide (ITO) TCEs. By controllingthree independent variables (etching time, film thickness and periodicity), we could tune the SPR peakposition and their light transmission distributions flexibly. This made it very attractive in the potentialphoto-electric device applications from plasmon-enhanced broadband photovoltaic to SPR-basedchemo-and biosensors.(3) The photo-electrical applications of new type TCEs: In order to investigate the practical applicationof our new type TCEs, the ZnO and CdS thin films were deposited on the gold network electrodes.Obvious absorption enhancement was observed compared that on the ITO substrate, which was closelyrelated to the SPR effects. The photo-electrical properties were characterized using the surfacephotovoltaic spectrum. Our results showed that this new type TCEs can replace the traditional ITOconductive electrodes used in photo-electric devices. More importantly, some interesting experimentalphenomena were observed, which may resulted from the SPR effects of our TCEs. The experimental results needed to carry out further experiments for a clear interpretation and confirmation in the future.