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https://ptsldigital.ukm.my/jspui/handle/123456789/520494| Title: | Bandgap engineering of cadmium zinc sulfide as alternative buffer layer for heterojunction thin flim photovoltaic application |
| Authors: | Nurhafiza Kamaruddin (P80450) |
| Supervisor: | Akhtaruzzaman, Assoc. Prof. Dr. |
| Keywords: | Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia Photovoltaic cells Thin films Solar cells Heterojunctions |
| Issue Date: | 16-May-2019 |
| Description: | The absorber layer of copper-zinc-tin-sulphide (Cu2ZnSnS4@CZTS) in CZTS solar cells is a quaternary chalcogenide naturally p-type semiconducting material. CZTS has a direct optical band-gap of 1.5 eV, and the tunability of the bandgap makes it suitable to replace rare earth Copper-Indium-Gallium-Diselenide (CIGS) thin films for CIGS thin film solar cells. Kesterite CZTS material is therefore believed to be the substitutional earth-abundant, inexpensive and non-toxic material with unique optical properties. Furthermore, CZTS exhibits a high absorption coefficient (>104 cm-1). To date, the highest photon to current conversion efficiency achieved in laboratory scale CZTS/CdxZn(1-x)S heterojunction thin film solar cell is 9% and for Cd-containing CZCTS solar cells is 11.2%. As photovoltaic industries nowadays are expecting inexpensive and affordable process of fabricating thin film solar cell, a solution process of depositing CdxZn(1-x)S buffer layer for CZTS thin film solar cell is the main challenge. Hence, this study focuses primarily on the low-cost buffer layer deposition using atmospheric pressure metal organic chemical vapour deposition (APCVD) and chemical bath deposition (CBD) to assess the best option. Then, major emphasize is given to CZTS/CdxZn(1-x)S interfacial region with bandgap tuning by non-vacuum lowcost method to achieve 'spike-like' conduction band offset (CBO) and favourable valence band offset (VBO). Numerical simulation by Solar Capacitance Simulator (SCAPS) has been done, which shows that the performance of CZTS full cell is mainly influenced by variation of buffer layer bandgap (Eg). Furthermore, a chosen buffer layer with various bandgap and electron affinity were numerically analysed. It has been found that the optimum buffer layer possesses CBO of 0.35 eV and VBO of 0.2 to 0.4 eV, which has resulted in achieving the optimal photovoltaic performance (դ) of 20% with Voc of 1.0 V, Jsc of 25 mA/cm2 and FF of 80%, respectively. Initial experimental study focuses on the growth optimization of cadmium sulfide (CdS) from five different cadmium sources such as CdSO4, Cd(NO3)2, Cd(CH3COO)2, CdCl2 and CdI. The deposited CdS buffer layer were characterized by XRD, UV-VIS, surface profiler and Hall measurement for structural, optical and electrical characteristics. The thickness of CdS thin films increases from 70 nm to 170 nm as CBD deposition time increases from 10 minutes to 60 minutes, respectively. Crystallographic study shows a cubic (1 1 1) preferential growth plane for all CdS thin films. UV-Vis result indicates trivial changes in the optical bandgap as films exhibited the bandgap of 2.4 eV with 0.1 eV deviation. Initial devices of CZTS full cell using CdSO4 as cadmium source for CdS buffer layer showed photovoltaic responses. In the latter part, CdxZn(1-x)S thin films were deposited by both CBD and APCVD methods. Due to rapid deposition mechanism in APCVD, all films were found in the range of 200 to 300 nm of thickness. The optimized CBD and APCVD methods for CdZnS thin films have been adopted as the buffer layer in CZTS solar cells and initial photovoltaic performances have been verified by Light I-V measurement. However, extensive optimization is needed especially for APCVD process that includes layer thickness control, interface with CZTS absorber, related other film quality such as optical and electrical properties to extract the latent potential of these buffer layers deposited in non-vacuum and cost efficiency ways presented in this study.,Ph.D.,Certification of Master's / Doctoral Thesis" is not available" |
| Pages: | 174 |
| Call Number: | TK8322.N837 2019 3 tesis |
| Publisher: | UKM, Bangi |
| Appears in Collections: | Solar Energy Research Institute / Institut Penyelidikan Tenaga Suria (SERI) |
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|---|---|---|---|---|
| ukmvital_121784+SOURCE1+SOURCE1.0.PDF Restricted Access | 27.96 MB | Adobe PDF |  View/Open |
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