The effect of cobalt-zinc substitution in CZTS thin film based solar cell Cu2CoxZn(1-x)SnS4

• Main Author: Gani, Tri Prasetia
• Other Authors: Lydia Helena Wong
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Materials
• Online Access: http://hdl.handle.net/10356/74638
• Institution: Nanyang Technological University

With the demand of finding alternatives energy source, solar cells research has been heightened for the past few years, especially Cu2ZnSnS4 (CZTS) thin film solar cell. With its non-toxic and abundant elemental material, CZTS clearly have some advantages over its predecessor, CuInGaSe2 (CIGS) and Cadmium Telluride (CdTe). However, CZTS itself also faced several challenges. One of them is its low efficiency performance compared to CIGS and CdTe. Such difference can be explained by low open circuit voltage (Voc) which is attributed to the presence of various defects within the CZTS thin films. One of the most prominent defects is the CuZn anti-site, where Zn and Cu exchange position within the crystal structures causing crystallographic disorder due to their similarity in terms of ionic size. Such defect can be minimized by substituting Zn with other bivalent metals (Cobalt) that have significant difference in size. Thus this report focuses on fabricating Cu2CoxZn(1-x)SnS4 thin film, with different Cu/Zn ratios. Cu2CoxZn(1-x)SnS4 thin films were successfully synthesized on Molybdenum-coated glass by chemical spray pyrolysis (CSP) technique. Investigation of the crystal structure, thickness, surface morphology, elemental composition, optical properties and electrical properties of Cu2CoxZn(1-x)SnS4 thin films were conducted to study their viability as an absorber layer. XRD results showed that the fabricated CCoZnTS thin films were kesterite structure. Thickness and surface morphologies results showed that it is possible that as Co concentration increase, the crystal grains decrease in size leading to more grain boundaries. Whereas, EDX was conducted in order to confirm the incorporation of Cobalt within the thin film, which was shown to be successful. Based on the optical properties and Hall measurement, it was observed that the thin film showed metallic characteristic at higher Co concentration. With possible defects in the system (secondary phase and grain boundaries), it was predicted that the performance of solar cells will decrease as x increase. To further confirm such assumption, the produced thin films were fabricated into solar cells devices, where the performance was tested on solar simulator. The efficiency of the solar cells decreased from 3.12% to 0.18% from x=0 to x=0.1. Above x=0.1, the solar cells showed no photo response.