Page - 114 - in Photovoltaic Materials and Electronic Devices

Multi-MaterialFrontContact for19%Thin FilmSolarCells JoopvanDeelen,YaseminTezsevinandMarcoBarink Abstract: The trade-off between transmittance and conductivity of the front contact material poses a bottleneck for thin film solar panels. Normally, the front contact material is a metal oxide and the optimal cell configuration and panel efficiency were determined for various band gap materials, representing Cu(In,Ga)Se2 (CIGS), CdTeandhighbandgapperovskites. Supplementingthemetaloxidewithametallic coppergrid improves theperformanceof the frontcontactandaimsto increase the efficiency. Various front contact designs with and without a metallic finger grid were calculated with a variation of the transparent conductive oxide (TCO) sheet resistance, scribingarea, cell length,andfingerdimensions. Inaddition, thecontact resistance and illumination power were also assessed and the optimal thin film solar panel design was determined. Adding a metallic finger grid on a TCO gives a higher solar cell efficiency and this also enables longer cell lengths. However, contact resistance between the metal and the TCO material can reduce the efficiency benefitsomewhat. Reprinted from Materials. Cite as: van Deelen, J.; Tezsevin, Y.; Barink, M. Multi-MaterialFrontContact for19%ThinFilmSolarCells. Materials2016,9, 96. 1. Introduction Photovoltaics (PV) is a wide arena for materials science to demonstrate the power of bringing different materials together in one device. There are two main material based photovoltaic families: one is Si wafer based and the other is thin film PV, which relies on coating of high quality materials on a substrate [1]. Even though thinfilmPVisbasedon“simple”coatingsteps, thesolarpowerconversionefficiency hasbeen improvedtovalueswellabove20%andapproaches thevaluespreviously onlyreachedbySi recordcells [2,3]. Oneof themaindriversbehindthissuccess is material improvement. In addition, interface issues have been tackled. For instance, recentlybacksurfacepassivation inCIGScellshasbeenimproved[4,5]. However, unlike forSiwaferbasedtechnologies, thestunning laboratorycelladvanceshave not translated into20%solarpanelefficiencies. Two of the bottlenecks for thin film solar panels are the active area loss due to interconnection and losses in the transparent front contact, for which usually a transparent conductive oxide (TCO) is coated [6,7]. The loss in active area should be reduced and we detail its impact on overall cell and front contact design in the Results Section. The TCO inevitably has a trade-off between conductivity and 114