Electrodeposition Preparation And Properties Investigation Of The Absorption Layers For CdTe Thin Film Solar Cells In Substrate Configuration

In recent years,because of the increasing consumption of fossil fuels,the greenhouse effect and energy security issues,many countries are paying close attention to the progress of renewable clean energy technologies,especially solar photovoltaic cells.At present,the crystal silicon cells are the most important products in the PV market.But the crystal silicon cells are much too delicate and so costly,which limits its scope of application and fields.Because of its advantages of high conversion efficiency and low production cost,the thin film solar cells are widely concentrated.Due to the low cost,a simple structure,no degradation,high conversion efficiency（>10%）,etc,CdTe solar cell is the first one to obtain high market share product using the film technology.To prepare a CdTe cell with high conversion efficiency,it must to meet three requirements:high-quality CdTe layer as the optical absorption layer,high-quality p-n heterojunction and the back contact layer.Electrodeposition is a proven method to prepare CdTe film with the advantages of low cost,low temperature,environmental friendliness and large-scale utility.In this work,we utilized the electrodeposition method to synthesize Cd Te micro-/nanoscale structures on Nickel（Ni）foil by changing the deposited potential or sulfuric acid concentration of the electrolyte.Meantime,we prepared a CdTe cell modular in substrate configuration solar cells by electrodeposition combined with water-bath method.In addition,the thickness of the Te diffusion barrier on the photoelectric conversion efficiency was discussed.The main contents of this paper are as follows:（1）On the Ni foils,CdTe films with various novel morphologies were prepared by electrodeposition an electrolyte with different H₂SO₄ concentrations or at different deposited potential.These synthesized CdTe films were cubic phase and showed an oriented growth along the[111]direction.By decreased the sulfuric acid concentrations or deposited potential,Te content increased in the film,which indicated lower H₂SO₄ concentrations or deposited potential were favorable for the formation of Te.We found the films were formed uniform distribution of Cd and Te elements,and element Te existed in the films（2）We believed that the morphology of the final product was obviously influenced by the presence of excess Te.The presence of excess Te which was influenced by the deposited potential and H₂SO₄ concentration in the electrolyte were closely related to the micro-/nanostructure and morphology of the CdTe film.It should be noted that the enhancement of the conversion efficiency was not only attributed to preferable absorption ability and a proper optimum band gap for the solar irradiation spectrum but also attributed to the high specific surface area of the micro-/nanostructures.The conversion efficiency of CdTe films mainly depended on the charge-carrier mobility.The high specific surface area was advantageous to enhance the carrier lifetime and hall mobility.In addition,since the photocurrent was confined chiefly by the transportation and collection of photoinduced charge carriers,the higher specific surface area enhanced the contact areas to the sunlight and soaked up a maximum amount of light.Additionally,the vertical growth structure shortened the pathways to transfer electrons more effectively.According to the above analyses,the morphologies based on different concentrations of sulfuric acid efficiently improved the optical properties and photoelectric performances of the CdTe films.The optical properties and photoelectric performances made the CdTe films deposited on Ni foils suitable as potential candidates for substrate configuration photoelectric conversion devices.（3）[101]preferred oriented spherical granular films of Te were successfully prepared via electrodeposition on Ni foils.Te could react with Ni to form NiTe₂which could form ohm contact with CdTe at 400℃.At the same time diffusion of Ni could be avoid by the Te layers,so the Te layers as the diffusion barriers was necessary in the CdTe cells in substrate configuration.The thickness of the Te diffusion barriers depended on the reaction time.（4）First,we prepared Te layers and CdTe layers on the Ni foils,then the CdS films were synthesized on the CdTe by the water-bath method and the composite films were heat by CdCl₂ at 450℃.The growth relationship between CdTe and CdS or CdTe and Te were perfect.The CdTe cells based on the Te with thickness 290nm had the best performance,the parameters of the photoelectric properties were V_OC=0.74V,J_SC=12.28 mA/cm²,FF=0.67,η=6.11%.A suitable Te thickness would increase the photoelectric properties but an over thick of Te layer would decreased the performances of the CdTe cells.