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

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, optimized and simulated in Silvaco TCAD. Finite Element Analysis (FEA) has been carried out to cater all physical and numerical models to generate practical results. For improvement in cell efficiency, a 1.52 eV wide-bandgap p-layer of CdTe is used which specifically improves the short circuit current (JSC). JSC is directly involved in the improvement of conversion efficiency. For the active region, an intrinsic CdTe layer is combined with an intrinsic amorphous silicon (a-Si) layer. This combination of intrinsic layers in active region is responsible for maximum absorption of photons with a wide range of energies and results in additional electron hole pair generation. Selective absorption is used to maximize light trapping and strong scattering of incident light into active region. Indium Tin Oxide (ITO) is used as front layer and back contact layer with Aluminum (Al) because it offers low resistivity of ~10-4 Ωcm and a transmittance of greater than 90%. Results have been validated by implementing two reported cells with p-i-i-n and p-i-n structures. The results indicate achievement of 28.05% conversion efficiency of the proposed heterojunction cell. The achieved efficiency is better than the efficiencies of the related cells compared in this work and also higher than that of the 25.6% of conventional Heterojunction Intrinsic Thin-film (HIT) silicon solar cells.