Silicon rich carbide as a conductive substrate for Si QD solar cells

Abstract

Silicon quantum dot (Si QD) tandem solar cell is a promising cell structure for realising high efficiency at low cost. The tandem solar cell effectively harnesses energy from the solar spectrum by stacking two or more cells together in the order of descending band gaps. Due to quantum confinement, the band gap of silicon based nanostructures such as Si QDs can be tailored by varying the size of the QDs. Solar cells and light emitting diodes based on Si QDs have been realised in experiments. However, current crowding due to high lateral resistance remains to be a major problem for Si QD devices grown on quartz substrates. Annealed silicon rich carbide (SRC), owing to its electrical conductivity, thermal stability and energy band gap compatible with Si QD cell fabrication, has the potential to overcome this problem. Further, this quasi-transparent thin-film can be used as either substrate or superstrate of a Si QD solar cell and therefore provides flexibility in cell structure design. Here, we investigate the physical, optical and electrical properties of the new material as functions of silicon concentration and doping conditions via a number of characterisation techniques including X-ray diffraction, Raman spectroscopy, ultraviolet-visible-infrared spectroscopy and four-point probe measurement. Some discoveries, including the lower crystallisation temperature of SiC within SRC, are also discussed. The research may provide some insight into the optimisation of annealed SRC as the new conductive material for Si QD solar cell and may boost the final arrival of all-silicon tandem solar cell.