Page - 157 - in Photovoltaic Materials and Electronic Devices

It is interesting to note that the ITO films processed at the 0.4 sccm oxygen flow rate presented the greatest resistance to acid etching in addition to exhibiting above moderateelectricalandopticalproperties. Thesefilmsshowpotentialascandidate materials for encapsulation of PV devices or transparent conducting electrodes for varied application in acid-rich environment. However, further research into optimizationofanti-acid(acidresistant)ITOfilmswillberequiredbeforethematerial canbe implemented incommercialPVdevices. Usually ITOissputtered invariedcombinationsof reactivegasenvironments of argon with oxygen, hydrogen and nitrogen [40]. The oxygen ambient has been shown to be an important parameter to control electrical and optical properties. The highestoxygenconcentrationsenhance the transmissionpropertyandtheoxygen deficientnature (oxygenvacancies) increasedtheelectrical conductivityof the ITO thinfilms[47,48]. Hence,asufficientamountofoxygenconcentrationcanimprove the opto-electronic performance of ITO thin films. High-quality ultra-thin ITO films are a needed significant step towards the realization and possible commercialization ofplasmonic-baseda-Si:Hthin-filmPVdevices [15,24,36–38]. Thesedeviceshavea potential to transformthethin-filmbasedsolarcells industrydueto their lowcost and ease of fabrication. In addition, plasmonic-enhanced PV has the potential to exhibit sophisticated light management schemes enabling unprecedented control over the trapping and propagation of light within the active region of the PV device [15], which would be expected to result in record-high device solar energy conversionefficiencies. 5. Conclusions Inthisstudy,ultra-ITOthinfilmshavebeenRFsputterdepositedusingdifferent oxygen flow rates and chemical shaving is performed at room temperature for different time periods. The thicknesses of the films are altered as a result from 89 nm to22nm. In-betweeneachetchingprocesscycle, thefilmswerecharacterizedforboth electricalandopticalproperties. Generally, the transmittanceof the ITOfilmswas observedto increasewithdecreasingfilmthickness,while theelectricalproperties wereobservedtodegradefor thesamefilms. Thiswasattributedto thedistortion of the In–Olattice long-rangeorderdueto thereductionreactionbetweentheITO and the etchants (acids). The novel method of chemical shaving further investigated here, is a simple and low-cost method with the potential to produce low loss and highly conductive ultra-thin and acid resistant ITO films for applications ranging from PV devices transparent electrodes to anti-acid materials. Using this method, ultra-thin ITOfilmswithrecord lowresistivityvalues (as lowas5.83ˆ10´4Ω¨cm) were obtained and the optical transmission is generally high in the 300–1000 nm wavelength region for all films. The etching rate strongly depends on the oxygen concentrations of RF sputtered ITO films as well as on the post process annealing. 157