Characterization and contact resistivity studies of ito thin films for use in silicon heterojunction solar cells

Güler, Seçil
Transparent conductive oxides (TCO) are widely used in optoelectronic devices such as flat panel displays and solar cells. Indium tin oxide, due to its wide optical bandgap and high transmittance in the visible spectrum, is commonly used for device applications such as anti-reflective coating, front TCO layer in silicon heterojunction solar cells. When ITO is used as TCO layer, the carrier transport mechanism through the junction is improved due to the decrease in the free carrier absorption. In this study, the effect of deposition conditions of ITO thin films on the material properties, as well as the material optimization towards the decrease of resistivity and carrier concentration simultaneously and the increase of the transparency and mobility values have been investigated. In order to achieve this goal, ITO thin films with various thicknesses were deposited on borosilicate glass substrates and n type silicon wafers by RF (Radio Frequency) magnetron sputtering using different deposition conditions. The main sputtering parameters were the sputtering power, substrate temperature, deposition pressure and oxygen content in the gas mixture. ITO films deposited under different conditions have been characterized in order to determine the optimum deposition parameters leading to ITO thin films with high conductivity, vi high transmittance in the visible range as well as the low carrier concentration. The structural, morphological, electrical and optical properties of the deposited ITO films have been characterized by X-Ray Diffraction, Atomic Force Microscopy (AFM), four-point-probe, Hall Effect and spectrophotometric measurement techniques. Besides the optimization studies of ITO thin films for Silicon Heterojunction Solar Cells, the specific contact resistivity studies between ITO and different layers in SHJ structure have been also carried out by using one dimensional transfer length method (1D-TLM). In the last part of the thesis study, different optimized ITO layers were deposited as an anti-reflective coating layer in SHJ solar cells and effect of ITO film properties on SHJ cell parameters have been investigated.