Performance Evaluation of an Improved Double Intrinsic Layer CdTe/a-Si Thin Film Photovoltaic Cell

Abstract

This paper presents a 1μm×1.25μm×1μm heterojunction thin film photovoltaic cell having “p-i1-i2-n”cell structure. The designed “ITO/p-CdTe/i1-CdTe/i2-a-Si/n-a-Si/ITO” photovoltaic cell is investigated, optimizedand simulated in Silvaco TCAD. Finite Element Analysis(FEA) has been carried out to cater all physical andnumerical models to generate practical results. Forimprovement in cell efficiency, a 1.52 eV wide-bandgap playerof CdTe is used which specifically improves the shortcircuit current (JSC). JSC is directly involved in theimprovement of conversion efficiency. For the active region,an intrinsic CdTe layer is combined with an intrinsicamorphous silicon (a-Si) layer. This combination of intrinsiclayers in active region is responsible for maximumabsorption of photons with a wide range of energies andresults in additional electron hole pair generation. Selectiveabsorption is used to maximize light trapping and strongscattering of incident light into active region. Indium TinOxide (ITO) is used as front layer and back contact layerwith Aluminum (Al) because it offers low resistivity of ~10-4Ωcm and a transmittance of greater than 90%. Results havebeen validated by implementing two reported cells with p-ii-n and p-i-n structures. The results indicate achievement of28.05% conversion efficiency of the proposed heterojunctioncell. The achieved efficiency is better than the efficiencies ofthe related cells compared in this work and also higher thanthat of the 25.6% of conventional Heterojunction IntrinsicThin-film (HIT) silicon solar cells