Numerical simulations of the current-matching effect and operation mechanisms on the performance of InGaN/Si tandem cells

Abstract

Numerical simulations are conducted to study the current-matching effect and operation mechanisms in and to design the optimized device structure of InGaN/Si tandem cells. The characteristics of short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and conversion efficiency (η) of InGaN/Si tandem cells are determined by the current-matching effect. The similar trend of η to that of Jsc shows that Jsc is a dominant factor in determining the performance of InGaN/Si tandem cells. In addition, the combined effects of the Jsc, Voc, and FF lead to an optimized η in the medium-indium, [InlineEquation not available: see fulltext.], InGaN/Si tandem cell. At [InlineEquation not available: see fulltext.], the Jsc of the InGaN subcell is equal to that of the Si subcell such that an InGaN/Si tandem cell reaches the current matching condition to operate at the maximum power point. Similar to the Jsc and FF, the η for low- [InlineEquation not available: see fulltext.] and high-In [InlineEquation not available: see fulltext.] InGaN/Si tandem cells are InGaN- and Si subcell-limited, respectively. Furthermore, the p- and n-layer thicknesses, indium content, and position of depletion region of InGaN subcell should be adjusted to reapportion the light between the two subcells and to achieve the maximum conversion efficiency. With appropriate thicknesses of p- and n-InGaN, In0.5–0.6Ga0.5–0.4 N/Si tandem cells can exhibit as high as approximately 34% to 36.5% conversion efficiency, demonstrating that a medium-indium InGaN/Si tandem cell results in a high-efficiency solar cell. Simulation results determine that the current-matching effect and operation mechanisms of InGaN/Si tandem cells can be utilized for efficiency enhancement through the optimized device structures.