Fabrication And Performance Optimization Of Cadmium Selenide Thin Film Solar Cells

Photovoltaic power generation is one of the effective ways to solve energy shortage and environmental pollution.Currently,the market share of silicon-based solar cells in the photovoltaic market is more than 90%.Improving the power conversion efficiency of silicon-based solar cells can greatly reduce the cost of photovoltaic power generation,which makes the feed-in price of photovoltaic power lower than traditional firepower generation.A top cell with a bandgap of～1.7 eV is preferred to match with Si bottom-cell and can achieve high efficiency of 45%in a tandem solar cell,which is an effective way to achieve efficiency breakthroughs.Many semiconductor materials with a bandgap of 1.7 eV have succeeded applications in Si tandem solar cells,such as the perovskites and III-V materials.However,their commercialization has been limited by the poor long-term stability of perovskites and the high manufacturing cost of III-V semiconductors.CdSe has great potential as the top cell of silicon-based cells with a bandgap of 1.7 eV,and it has the advantages of high crustal abundance,low price,good material stability,and excellent photoelectric properties.However,the systematic study of CdSe thin-film solar cells from material to the device is lacking.In this paper,the preparation of CdSe film,the materials,and the photoelectric properties of CdSe were systematically studied.Combined with the device structure optimization,the device performance was gradually improved.The main contents are as follows:（1）CdSe films were prepared by the rapid thermal evaporation（RTE）method,and their materials and photoelectric properties were characterized.The influences of substrate temperature,evaporation temperature,and evaporation time on the deposited film were systematically studied.The thickness of CdSe films was precisely controlled by changing the evaporation time.High-quality CdSe films with hexagonal wurtzite phase,micron grain size,and dense quality were obtained at the substrate temperature of 400^°C and evaporation temperature of 800^°C.The characterization of the photoelectric properties of CdSe films confirmed that CdSe has a suitable bandgap of 1.7 eV,a high absorption coefficient of 10⁵cm^-1,and a narrow full-width half-maximum of photoluminescence peak with 23 nm,which demonstrate the potential of CdSe as absorption layer of top cell in Si tandem solar cell.（2）The CdSe thin-film solar cell was successfully prepared with a device efficiency of 1.88%.First,by combining organic and inorganic hole transport layers,the Cu I/PEDOT double hole collection layer is applied and achieves a device with an efficiency of 0.6%.The subsequent application of the Zn O/Cd S electron transport layers effectively reduced the leakage problem and further increased the device efficiency to 1.50%.Based on the FTO/Zn O/Cd S/CdSe/PEDOT/Cu I/Au device structure,the thickness of the CdSe absorption layer was further optimized.When the CdSe film was 500 nm thick,the highest photoelectric conversion efficiency of the device was 1.88%,with 0.501 V open voltage,58.1%fill factor,and 6.45 m A cm^-2current density.