Abstract
Usually a buffer layer of cadmium sulphide is used in high efficiency solar cells based on Cu(In,Ga)Se2(CIGS). Because of cadmium toxicity, many in-vestigations have been conducted to use Cd-free buffer layers. Our work focuses on this type of CIGS-based solar cells where CdS is replaced by a ZnS buffer layer. In this contribution, AFORS-HET software is used to simulate n-ZnO: Al/i-ZnO/n-ZnS/p-CIGS/Mo polycrystalline thin-film solar cell where the key parts are p-CIGS absorber layer and n-ZnS buffer layer. The characteristics of these key parts: thickness and Ga-content of the absorber layer, thickness of the buffer layer and doping concentrations of absorber and buffer layers have been investigated to optimize the conversion efficiency. We find a maximum conversion efficiency of 26% with a short-circuit current of 36.9 mA/cm2, an open circuit voltage of 824 mV, and a fill factor of 85.5%.
Highlights
Cu(In,Ga)Se2 is one of the most promising semiconductor materials for photovoltaic conversion based on polycrystalline thin-films
Our work focuses on this type of CIGS-based solar cells where CdS is replaced by a ZnS buffer layer
Keeping the absorber layer doping at 5 × 1017 cm−3, Figure 4(b) and Figure 4(d) shows that the solar cell characteristic parameters change slightly above a buffer layer doping of 1018 cm−3, but drop strongly below this doping level because the Fermi level is no longer pinned, except for Voc that is almost constant at all doping levels
Summary
Cu(In,Ga)Se2 is one of the most promising semiconductor materials for photovoltaic conversion based on polycrystalline thin-films. We turn to CIGS solar cells with a ZnS buffer layer and calculate their main electrical characteristics: short circuit current, open circuit voltage, fill factor and total conversion efficiency, when varying successively the above mentioned parameters. This computation procedure allows us to predict the optimal values of the investigated parameters when replacing CdS by ZnS buffer layer, and to get insight into the sensitivities of the electrical characteristics of the solar cells with respect to variations of each single parameter.
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