CZTSSe thin film : growth, characterization and solar cell applications

Terlemezoğlu, Makbule
Cu2ZnSn(S,Se)4 (CZTSSe) compound is one of the most promising absorber materials for thin film solar cell technology due to the abundance and non-toxicity of its constituents. Besides, CZTSSe has an ideal direct band gap value in the range of 1-1.5 eV and high absorption coefficient (> 104 cm-1) in the visible region, which satisfies the conversion of the maximum amount of energy of the solar spectrum. For this, CZTSSe absorber layer with only a few microns of thickness is sufficient to absorb all the photons having the energy greater than its band gap. Another advantage is that its crystal structure is very similar to chalcopyrites. For this reason, CZTSSe thin film based solar cells are fabricated in a similar manner to chalcopyrite based solar cells. This study focused on the growth, characterization, and photovoltaic applications of CZTSSe thin films. In this context, firstly, CZTSSe thin films were grown by using thermal evaporation method on both glass and silicon (Si) substrates. During the deposition process, sintered crystalline powder of CZTSSe was used as the evaporation source to obtain CZTSSe thin films in an efficient and cost-effective way. Post annealing process was applied to increase the homogeneity of the deposited thin films. Subsequently, the characterization of annealed films was carried out. Then, the electrical properties of the CZTSSe/Si structure were investigated using temperature-dependent current-voltage (I-V) and frequency dependent capacitance-voltage (C-V) measurements for possible future applications in various technologies. Also, in this study, CZTSSe thin films having a surface decorated with self-assembled nanoflakes were fabricated by utilizing the RF magnetron sputtering method. It was observed that the self-assembled nanostructures on the surface of the film yield low surface reflectance. The formation of nanoflakes was investigated. It was observed that the size of nanoflakes can be adjusted by an accurate control of the sputtering process, including film thickness. Moreover, the effect of substrate temperature on the formation of nanoflakes at the film surface was discussed at a fixed deposition route. In the last part of the thesis, CZTSSe thin film based solar cells were fabricated in superstrate configuration. For this purpose, the performance of glass/ITO/CdS/CZTSSe/metal structure was investigated. Then, the effect of titanium dioxide layer (TiO2) on the device performance was examined due to its being a hole blocking and wide band gap material properties. As a result, the considerable positive effect of TiO2 layer on the open circuit voltage was observed.


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Citation Formats
M. Terlemezoğlu, “CZTSSe thin film : growth, characterization and solar cell applications ,” Thesis (Ph.D.) -- Graduate School of Natural and Applied Sciences. Physics., Middle East Technical University, 2019.