Abstract
The aim of this work is to analyze the influence of the interfacial MoSe2 layer on the performance of a /n-ZnO/i-ZnO/n-Zn(O,S)/p-CIGS/p+-MoSe2/Mo/SLG solar cell. In this investigation, the numerical simulation software AFORS-HET is used to calculate the electrical characteristics of the cell with and without this MoSe2 layer. Different reported experimental works have highlighted the presence of a thin-film MoSe2 layer at the CIGS/Mo contact interface. Under a tunneling effect, this MoSe2 layer transforms the Schottky CIGS/Mo contact nature into a quasi-ohmic one. Owing to a heavily p-doping, the MoSe2 thin layer allows better transport of majority carrier, tunneling them from CIGS to Mo. Moreover, the bandgap of MoSe2 is wider than that of the CIGS absorbing layer, such that an electric field is generated close to the back surface. The presence of this electric field reduces carrier recombination at the interface. Under these conditions, we examined the performance of the cell with and without MoSe2 layer. When the thickness of the CIGS absorber is in the range from 3.5 μm down to 1.5 μm, the efficiency of the cell with a MoSe2 interfacial layer remains almost constant, about 24.6%, while that of the MoSe2-free solar cell decreases from 24.6% to 23.4%. Besides, a Schottky barrier height larger than 0.45 eV severely affects the fill factor and open circuit voltage of the solar cell with MoSe2 interface layer compared to the MoSe2-free solar cell.
Highlights
High efficiency CIGS-based solar cells have been the focus of several years of theoretical and experimental research
When the thickness of the CIGS absorber is in the range from 3.5 μm down to 1.5 μm, the efficiency of the cell with a MoSe2 interfacial layer remains almost constant, about 24.6%, while that of the MoSe2-free solar cell decreases from 24.6% to 23.4%
The conversion efficiency obtained for the MoSe2-free solar cell η = 24.6% is equal to that of the cell including a MoSe2 thin-film layer at the CIGS/Mo contact interface
Summary
High efficiency CIGS-based solar cells have been the focus of several years of theoretical and experimental research. The recent high laboratory efficiency values of 22.9% and 23.4% (Solar Frontier) [1] [2] are close to the efficiency of 25% achieved by crystalline silicon solar cells. These thin-film cells have achieved the best performance of all second-generation cell technologies. Data about the material’s properties strongly depend on the used growth process and characterization techniques [3] [4] This entails input parameters of simulation works may vary within wide ranges, imposing some limitation on the accuracy of simulated results. CIGS (namely CuIn1−xGaxSe2) material remains one of the most promising semiconductor materials for photovoltaic conversion based on polycrystalline thin-films because of several favorable properties: 1) Its bandgap can be varied continuously by changing the gallium content, x, and its value is given by the commonly used formula (all bandgap energies in eV) [5] [6] [7]:
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