Research On Preparation Of CuInS₂ And CuInSe₂ Thin Films By Electrodeposition Method

With the increasing decrease of conventional fossil energy, solar energy, as one kind of significant renewable energy, has becoming a focus. The photovoltaic technology is one of the most important development aspects in the utilization field of solar energy. In the past decades, photovoltaic industry in the world developed rapidly. The further massive application of crystalline silicon solar cells, accounting for more than 90% of the world photovoltaic market at present, is prevented by the high production cost of solar cells due to the costly price of high purity silicon raw material and high energy consumption in the production process. Recently, thin film solar cells with the predominance of low cost and high performance have attracted much attention. I-III-VI2 family compound thin film cells such as CuInS₂ and CuInSe₂ (CIS), with high theoretical photoelectric conversion efficiency, direct band gap, optimum width of band gap, extraordinarily high absorption coefficient and long-term stability, are considered promising candidates for next generation solar cells.Although generally vacuum deposition techniques fabricate high quality CIS thin films, the production cost is high due to vacuum equipments and rigorous techniques. Preparation of CIS thin films by non-vacuum deposition techniques such as spray, particle-coating and electrodeposition, with a good development foreground, needs inexpensive equipments and low investment capital. Not only the production cost of thin films is low, but also large-area preparation of CIS thin films is feasible. Large-scale industrialization of CIS thin film solar cells is promising to come true.The thickness of CIS thin films prepared by electrodeposition method is easy to control. Precursor thin films can be deposited on large size and complicated shape substrates. The electrodeposition process is at room temperature, so it consumes low energy. Three kinds of elements are reduced onto a substrate synchronously in one-step electrodeposition method, compared with two-step electrodeposition method. The composition of films can be controlled, and high quality films with few defects can be obtained. In this thesis, the CuInS₂ and CuInSe₂ thin films were prepared by one-step electrodeposition method. The precursor thin films and multicrystalline CIS thin films were analyzed and characterized. Moreover, the primary archetypal CuInS₂ thin film solar cell devices were fabricated.The following results have been obtained:1. Uniform and compact CuInS₂ thin films with different Cu/In ratio were prepared by one-step electrodeposition method. They're p-type chalcopyrite semiconductors with direct band gap of about 1.47 eV and thickness of about 1～2μrn. The influences of applied potential, substrates, Cu/In ratio, pH value, the concentration of citric acid sodium and raw material in the precursor thin films and the effect of post anneal treatment conditions on multi-crystalline CuInS₂ thin films were studied.2. The CuInS₂ thin film solar cells with a configuration of Mo/CuInS₂/CdS/ZnO/ITO/C, fabricated on CuInS₂ thin films prepared by one-step elecrodeposition, take on the photovoltaic characteristic. The average values of V_oc, I_sc and FF are 350 mV, 3 mA/cm² and 20%, respectively. The highest conversion efficiency is 0.57%.3. Uniform and compact CuInSe2 thin films of chalcopyrite phase with a thickness of about 1～2μm were prepared by one-step electrodeposition method. The influences of applied potential and substrates in the precursor thin films and the effect of post anneal treatment conditions on multi-crystalline CuInSe2 thin films were studied.