A study of Cu2ZnSn(SxSe1-x)4 Thin Films Prepared by Sputtering Deposition and Their Applications to Thin-film Solar Cells
| Autor: | Lin, Yu-Pin, 林郁斌 |
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| Rok vydání: | 2017 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 105 This study prepares the 2-inch Cu2ZnSnS4 (CZTS) targets by the solid-state reactions of CuS, ZnS and SnS2 raw powders mixture. The powders were mixed at various Cu molar ratios of 2, 1.8 and 1.6, pressed into 6-mm pellet forms, and then sintered at temperatures ranging from 200 to 600C for 8 hrs. Accordingly, the correlations of powder constitution and heat-treatment conditions to the microstructure, composition and morphology of CZTS pellets were investigated. X-ray diffraction (XRD) and Raman spectroscopy analyses indicated that the sample prepared with the Cu molar ratio of 1.6 and sintered at 600C for 8 hrs forms the single-phase kesterite (KS) CZTS structure. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses revealed the Cu-poor/Zn-rich feature with the stoichiometry of Cu26.53Zn14.75Sn12.31S46.41. Afterward, the 2-inch CZTS sputtering target was prepared by utilizing the optimum sintering condition established by the study of 6-mm pellets. Microstructure and composition analyses indicated the CZTS target possesses the single-phase KS-CZTS structure and the stoichiometry of Cu26.55Zn15.00Sn12.32S46.14 with Cu-poor/Zn-rich feature. The 2-inch CZTS sputtering target was then transferred to a sputtering system for depositing the CZTS photo-absorption layers at working pressures of 1, 5 and 10 mtorr. Follwed by the annealing at 570C for 1 hr in sulfur (S) vapor ambient, the single-phase, Cu-poor/Zn-rich CZTS layer with the stoichiometry of Cu24.15Zn14.73Sn10.75S50.37 was achieved in CZTS layer deposited at 1 mtorr. Moreover, it possessed the bandgap (Eg) of 1.5 eV, p-type carrier concentration (N) of 2.81017 cm3 and mobility () of 8.61 cm2V1sec1. Such a CZTS layer was implanted in the thin-film solar cells with the device structure of Mo/CZTS/CdS/i-ZnO/IZO/Al. Under the AM1.5 illumination condition, the CZTS thin-film solar cell sample with the open-circuit voltage (Voc) of 0.52 V, short-circuit current (Jsc) of 19.17 mAcm2, the fill factor (FF) of 52.7%, the conversion efficiency () of 5.2% and the external quantum efficiency (EQE) of 60% was achieved. In order to further enhance the efficiency of CZTS device, selenium (Se) was added into the CZTS to form the Cu2ZnSn(SxSe1-x)4 (CZT(SSe)) photo-absorption layer and their microstructure, composition and physical properties were investigated. The CZT(SSe) layers were prepared by sputtering deposition using single-phase CZTS target followed by annealing treatment at 570C for 1 hr in the ambient with various Se/S ratios (0, 0.5, 1, 4 and 10). Analytical results indicated the Cu-poor/Zn-rich CZT(SSe) layers with S/(S+Se) ratios in the range of 0.21 to 1 could be achieved and the CZT(SSe) layers were the mixture of KS-CZTS and KS-CZTSe phases. UV-NIR spectroscopy indicated the Eg’s of CZT(SSe) samples are in the range of 1.06 to 1.45 eV when the S/(S+Se) ratio varies from 0.21 to 1. Hall effect measurement observed the best transport property with p-type conduction, N of 2.171015 cm3 and of 8.9 cm2V1sec1 in CZT(SSe) layer with S/(S+Se) ratio of 0.46. Under the AM1.5 illumination condition, the CZT(SSe) thin-film solar cell sample with S/(S+Se) ratio of 0.46 exhibited the best performance with Voc of 0.506 V, Jsc of 27.41 mAcm2, FF of 50%, of 6.9% and EQE of 70%. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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