Effect of potassium and germanium dopants on optical, structural and electrical properties of copper zinc tin sulphoselenide solar absorber layer

• Main Author: Salleh, Mohd. Shahril
• Format: Thesis
• Language: English
• Published: 2020
• Subjects: QC Physics
• Online Access: http://eprints.utm.my/id/eprint/102267/1/MohdShahrilSallehMFS2020.pdf.pdf; http://eprints.utm.my/id/eprint/102267/; http://dms.library.utm.my:8080/vital/access/manager/Repository/vital:146321

In present research, the role of Potassium (K) and Germanium (Ge) dopants in Copper Zinc Tin Sulphoselenide (CZTSSe) absorber thin solar film prepared using non-vacuum spray pyrolysis deposition technique has been investigated. K-doped CZTS precursor solution was prepared using one-pot approach with different concentrations of K (0.0, 0.5, 1.0, 1.5, 2.0 and 2.5) mol %, dissolved using dimethyl sulfoxide solvent. The solution was then sprayed on soda lime glass (SLG) substrate using ultrasonic spray coater at 300 °C. The deposited thin films were selenized in tube furnace using three-step temperature approach (300 °C, 500 °C and 550 °C) with 30 minutes ramping time in nitrogen environment. Deposited K-doped CZTSSe thin films were characterized by ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy and 3D microscope to determine the optical properties and thickness of K-doped CZTSSe structure. X-ray diffractometer was employed for the structural and crystallinity analyses, whereas field emission scanning electron microscope was used to study surface morphologies. Energy dispersive X-ray spectrometer was used to study the elemental composition of the film while Hall effect measurement system was used for measuring the charge carrier density. Based on results, 1.5 mol % of Kdoped was selected for fabrication process of (K,Ge)-doped CZTSSe solar absorber layer. Same processes were performed to synthesize thin films except with different molar concentrations of Ge (10, 15, 20, 25 and 30)% in dimethylformamide as dissolving agent. The effects of different Ge concentrations were studied. UV-Vis- NIR spectra have shown high absorption coefficient which was more than 10000 cm-1 for each sample. The bandgap increased as the concentration of Ge was increased, which inferred the capability of Ge to tune the CZTSSe bandgap to increase the open circuit voltage. X-ray spectra showed better crystallinity at 25% and 30% of Ge dopant, while micrographs from field emission scanning electron microscope revealed that 25% Ge has better crystal growth. The charge carrier density in the absorber layer also increased with increase in dopant concentration. Based on the findings, (K,Ge)-doped CZTSSe thin film with 1.5 mol % K and 25% Ge has the best properties.