Hot-wire chemical vapor-deposited microcrystalline silicon in single and tandem n–i–p solar cells

Abstract

This paper examines the potential of μc-Si deposited by hot-wire chemical vapor deposition (HWCVD) at a constant hydrogen dilution of 0.95, as absorber layer in n–i–p thin film solar cells. For a series of single junction cells onto plain stainless steel, the highest open circuit voltage (Voc) and Fill Factor (FF) were 0.54V and 0.72. From J–V measurements at reduced light intensities, the change of the AM1.5-normalized FF values with light intensity was found to depend on the μc-Si i-layer thickness. This is attributed to the thickness evolution of the i-layer crystallinity, which influences the cell properties, particularly for i-layers thinner than 2.0μm. For thicker layers the measurements clearly show drift-driven charge carrier collection. Tandem cells showed FF values as high as 0.77, which indicates the very high optoelectronic quality of the μc-Si material. A 2.0μm cell on a textured back reflector shows an efficiency of 7.8%.