Quantum Dot Luminescent Downshifting Layer For Silicon Solar Cells

The crystalline silicon solar cells are most widely used semiconductor optoelectronic devices and most of studies have devoted to improve their photoelectric performance. Currently the device structure and antireflection coating technology has been optimized to enhance the conversion efficiency. However, the further improvement is limited due to the maturation of these technologies. As a result, new technology is needed to develop. It is known that the solar light is a continuous spectrum, and its distribution ranges from hundreds of nanometers to several microns. The band gap of silicon is about 1.12V. The crystalline silicon solar cells mainly absorb the light from 400nm to 900nm and the quantum efficiency is low for the light with wavelength below 400nm (violet or ultraviolet light), which causes a loss of solar energy. Therefore, it is necessary to take advantage of this part of solar energy in order to further improve the photoelectric conversion efficiency of solar cells.The quantum dot (QD) is the hot topic of current researches in optoelectronic materials and devices. Under the excitation of violet or ultraviolet light, many kinds of QDs can emit the visible light from 500nm to 700nm, which can be easily absorbed by crystalline silicon. Therefore, QDs are promising to be used as highly efficient luminescent downshifting materials in solar cells to improve their conversion efficiency.The content of this thesis is organized as follows:The first chapter introduces the background and working principle of solar cells, and the technologies to improve the conversion efficiency.The second chapter describes the preparation of silica by using sol-gel methods. Silica films with good performance were obtained by optizming the preparation conditions.The third chapter describes the preparation of CdS QDs by chemical bath method. By changing the reaction temperatures and surfactants, the CdS QDs with different optical properties are controllably obtained. The forth chapter introduces the preparation of CdS QD luminescent downshifting layer and their application in solar cells. The photovoltaic measurement shows the improvement of conversion efficiency of solar cells by using QD downshifting layer on their surface.