Abstract
Indium tin oxide (ITO) is a transparent conducting oxide (TCO) known for its high electrical conductivity and excellent visible light transparency and is widely used as a transparent electrode in solar cells. ITO thin films have been prepared by several methods including RF magnetron sputtering, DC magnetron sputtering, chemical vapour deposition (CVD) and chemical solution deposition (CSD). The simplicity and low cost of ITO thin films prepared by CSD through dip- and spin-coating has made this technique advantageous compared to other alternatives. However, until now ITO films produced by CSD have displayed low microstructural quality characterized by homogeneous crystallization. By adjusting the precursor composition and temperature treatment procedure a transition to heterogeneous crystallization was promoted. A columnar grain structure with preferred (111) orientation was observed. Various post-deposition treatments were used to improve the quality of CSD films deposited on n- and p-type Si substrates. Transmission electron microscopy, electrical conductivity measurements, ellipsometry, X-ray diffraction and atomic force microscopy were used for an analysis of the ITO films properties. The surface passivation properties were investigated by means of the effective recombination lifetime as measured by the quasi-steady-state photoconductance (QssPC) technique. It is found that the CSD ITO films have better passivation properties of silicon surface compared to magnetron sputtered ones. This result can be attributed to the “softer” conditions, which the CSD method provides. TEM analysis shows that layer-by-layer deposition of CSD ITO films provides a possibility to introduce nano-voids/nano-dots into this material during the processing, which is a promising approach for the third-generation photovoltaics. Application of CSD ITO films for the low-cost processing of heterojunction Si based solar cells are estimated and discussed.
