單一相Cu2ZnSnS4濺鍍靶材之製備及其應用於薄膜太陽能電池光吸收層之研究

Abstract

本論文研究使用CuS、ZnS及SnS2二元相粉體為起始原料，以固態燒結法製備2吋Cu2ZnSnS4（CZTS）單一四元相靶材，探討改變Cu莫耳比（2、1.8及1.6）、燒結時間（2至12 hrs）及溫度（200至600C）對靶材微觀結構、組成及表面形貌之影響。X光繞射（X-ray Diffraction，XRD）與拉曼光譜（Raman Spectroscopy）分析顯示，粉體莫耳比為Cu：Zn：Sn：S = 1.6：1：1：4、經600°C、8 hrs燒結之試片為單一Kesterite CZTS之相結構。掃描式電子顯微鏡（Field Emission Scanning Electron Microscopy，SEM）與能量散佈光譜儀（Energy Dispersive Spectroscopy，EDS）分析顯示，靶材之實際化學劑量比為Cu26.57Zn13.97Sn12.74S46.72，為接近理論化學計量比之貧銅/富鋅（Cu-poor/Zn-rich）組成。將上述燒結條件製成的2吋CZTS靶材在5及10 mtorr之工作壓力、基板不加熱的條件下濺鍍沉積CZTS光吸收層薄膜，經550C硫化退火處理後，XRD及Raman分析顯示薄膜均為單一相CZTS結構，EDS分析顯示其為Cu24.25Zn12.63Sn12.15S50.97之Cu-poor/Zn-rich組成，紫外光-可見光（UV-Visible）光譜分析顯示其能隙（Energy Bandgap，Eg）約1.4至1.5 eV及吸收係數（Absorption Coefficient，）分別為5.3104至3.2104 cm1，霍爾效應（Hall Effect）量測顯示CZTS薄膜均為p型化合物半導體，工作壓力5 mtorr製備之CZTS薄膜具有最佳的載子濃度為2.11016 cm3及載子遷移率為9.82 cm2V1sec1。在不同Cu含量對CZTS靶材及薄膜之組成影響的研究發現，Cu莫耳比為1.6及1.8所製備之CZTS靶材及薄膜均為單一相CZTS結構，Cu莫耳比為2所製備的薄膜因過量的Cu而出現CuS相；Hall效應分析顯示以Cu莫耳比為1.6所製備之CZTS薄膜具有最佳之傳輸性質。

This study prepares the 2-inch Cu2ZnSnS4 (CZTS) targets by the solid-state reaction of CuS, ZnS and SnS2 raw powders at various Cu molar ratios, reaction times and temperatures. Accordingly, the influence of powder constitution and heat-treatment conditions on microstructure, composition and morphology of CZTS targets were investigated. X-ray diffraction and Raman spectroscopy analyses indicated that the sample prepared at the powder ratio of 1.6:1:1:4 forms the single kesterite CZTS phase structure via the sintering at 600C for 8 hrs. Scanning electron microscopy/energy dispersive spectroscopy analysis revealed that the CZTS is of the Cu-poor/Zn-rich structure with the stoichiometric ratio of Cu26.57Zn13.79Sn12.74S46.72. The CZTS target was then transferred to a sputtering system for depositing the CZTS light absorption layers at working pressures of 5 and 10 mtorr. With a post annealing treatment at 550C for 1 hr in sulphur ambient, the single-phase, Cu-poor/Zn-rich CZTS thin film with the stoichiometric ratio of Cu24.25Zn12.63Sn12.15S50.97 was achieved. The bandgap and absorption coefficient of such a CZTS layer was 1.4-1.5 eV and 5.3104-3.2104 cm1 as characterized by UV-Visible spectroscopy. Hall-effect measurement found that the CZTS layers are p-type semiconductors and the CZTS layer deposited at working pressure of 5 mtorr exhibits the best carrier concentration of 2.11016 cm3 and mobility of 9.82 cm2V1sec1. Analytical results of CZTS targets prepared at various Cu contents iindicatd that the samples prepared at the Cu molar ratios of 1.6 and 1.8 are of the single-phase CZTS structure whereas the sample prepared at the Cu molar ratio of 2 contains the binary CuS phase. In conjunction with the results of physical property analyses, the CZTS target prepared at the Cu molar ratio of 1.6 was found to be suitable for photovoltaic applications.