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Title:	Fabrication of chromium doped copper-zinc-tin-sulphide intermediate band solar cell by magnetron co-sputtering technique
Authors:	Megat Mohd Izhar Sapeli (P83768)
Supervisor:	Nowshad Amin, Prof. Dr.
Keywords:	Solar cells Copper-zinc alloys Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia
Issue Date:	25-Oct-2018
Description:	Copper-zinc-tin-sulphide (CZTS) thin film solar cell is as an alternative to copper-indium-gallium-diselenide (CIGS) technology due to the usage of non-toxic and earth-abundant elements. Meanwhile, intermediate band solar cell (IBSC) technology progresses as well to suppress thermalization loss, by engineering three-step photoexcitation mechanisms. Combining both technologies, Density Functional Theory (DFT) study recently proposes chromium doped CZTS (CZTS:Cr) as the material for IBSC. However, impurity doping to realize an IBSC based on quaternary compound semiconductor does not attract much attention due to stoichiometric complexity involving five different elements. Additionally, theoretical study prediction that shows three distinguished peaks under absorption coefficient plot rarely obtained experimentally to confirm the existence of intermediate band. Hence, this study is conducted with the aim to focus primarily on the effects of chromium (Cr) doping into CZTS matrix deposited by co-sputtering technique. Major emphasize is given to optoelectronic property evolution with Cr-sulphur constitutions variation. Addition of Cr was observed to deteriorate the CZTS crystallinity mainly in the (112) direction, as well as inducing the growth of cubic-zinc-chromium-sulphide (cubic-ZnCr2S4) secondary phase as examined from the X-ray diffraction (XRD) pattern. Segregation of Cr-rich compound at the bottom of CZTS film as confirmed by energy dispersive X-ray (EDX) measurement prevents complete CZTS crystallization, resulting in a bilayer grain formation as observed from scanning electron microscopy (SEM) characterization. While bandgap is found to vary depending on Cr concentration, empirical calculation based on Lucovsky formula shows that insufficient Cr only creates defect state deep in the bandgap. At sufficiently high enough Cr content, additional absorption peak as a proof for intermediate band formation is realized from ultraviolet-visible (UV-VIS) measurement spectra. Sulphurization optimization takes the intermediate band into deeper level, from 0.17 eV to 0.62 eV above the valence band maximum (VBM). Preliminary CZTS:Cr IBSC device is fabricated using the optimized sputtering deposition power of 10 Watt-Cr and 50 Watt-stoichiometric CZTS, 400 Torr sulphurization pressure, 580 ˚C sulphurization temperature and 47.1 mg sulphur. Maximum photovoltaic conversion efficiency of 0.022 % is achieved for an active area of 0.25 cm2 with open circuit voltage (Voc) of 0.037 V, short circuit current (Isc) of 0.528 mA and fill factor (FF) of 26.1 %. This work confirms film deposited using stoichiometric CZTS target could be engineered to show IB properties whereas this is not the case for Cu-poor and Zn-rich target. The position of IB could be shifted by varying Cr-S content. Full device fabrication confirms pn-junction is formed and diode-like characteristic is achieved.,Ph.D.
Pages:	125
Call Number:	TK2960.M434 2018 3 tesis
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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