Optimization of the Asymmetric Intermediate Reflector Morphology for High Stabilized Efficiency Thin n-i-p Micromorph Solar Cells

Abstract

This paper focuses on our latest progress in n-i-p thin-micromorph solar-cell fabrication using textured back reflectors and asymmetric intermediate reflectors, both deposited by low-pressure chemical vapor deposition of zinc oxide. We then present microcrystalline bottom cells with high crystallinity, which yield excellent long wavelength response for relatively thin absorber thickness. In a 1.5-μm-thick μc-Si:H single-junction n-i-p solar cell, we thus obtain a short-circuit current density of 25.9 mA·cm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $^{-2}$</tex></formula> , resulting in an initial cell efficiency of 9.1%. Subsequently, the roughness of the intermediate reflector layer is adapted for the growth of high-performance amorphous silicon (a-Si:H) top cells. Combining bottom cells with high current, an optimal intermediate reflector morphology and a 0.22-μm-thick a-Si:H top cell, we reach high initial open-circuit voltages of 1.45 V, and we obtain a stabilized cell with an efficiency of 11.1%, which is our best stable efficiency for n-i-p solar cells.