Numerical simulation of quantum dots as a buffer layer in CIGS solar cells: a comparative study.

Quantum bandgap buffer layers can improve sunlight absorption in the short wavelength region, hence improving the performance of CIGS solar cells. In this study, we use numerical modelling to determine the impact of various buffer layers' electrical characteristics on the performance of CIGS thin film photovoltaic devices, particularly, carrier concentration and the quantum effect. As well Ag2S buffer layer has been experimentally examined to fulfilment its effect in term of bulk and quantum bandgap. Experimental results depicted that, Ag2S QDs has polycrystalline nature of films, with smooth surface roughness, and average diameter 4 nm. Meanwhile, a simulation revealed that the Fermi level of the (n-buffer layer) material shifts closer to the conduction band with an increase in carrier concentration. The findings indicate that, a buffer layer with a wider bandgap and carrier concentration is an essential demand for achieving a device with a higher conversion efficiency and a broader bandgap-CBO window. It was attributed to beneficial synergistic effects of high carrier concentration and narrower depletion region, which enable carriers to overcome high CBO barrier. Most importantly, modelling results indicate that the optic-electrical characteristics of the buffer layer are critical in determining the progress of a CIGS solar cell.

A historical review of gait analysis.

Healthcare professionals have long been concerned with the assessment of human gait, but only recently were they able to utilize instrumental gait analysis in routine clinical practice for diagnosis, and to guide the selection of treatment methods for complex musculo-skeletal and neurological disorders. The development of motion analysis systems has progressed through several stages from simple to more sophisticated, versatile, multimodal, and accurate equipment. Several computerized motion analysis systems are now commercially available for the measurement of human gait. These vary in their design and performance. The purpose of this review is to summarize briefly the history and advances in the technology of instrumental gait analysis, especially during the past 3 decades. Further, it is hoped that this review will give clinical practitioners and researchers a general insight into the variety of measurement systems that are currently available for gait analysis and enable them to make an informed choice of the motion analysis system that best suits their clinical needs.