Dissertations / Theses on the topic 'Cu2SnS3'

Commercially available high-performance thermoelectric materials are often rare or toxic and therefore unsustainable. The present thesis work makes a case for eco-friendly, earth-abundant, and non-toxic p-type ceramic Cu2SnS3 (CTS, hereafter) and, in general, the use of disordered materials for thermoelectric applications. The detailed study of polymorphism, synthesis conditions, porosity, grain size, and doping provides a systematic and in-depth experimental and computational analysis of thermoelectric properties and stability of CTS. These results can be generalized for numerous thermoelectric materials and other applications. Moreover, a case for functioning thermoelectric generators using non-toxic and cost-effective materials is also presented. The thesis begins with a brief introduction to thermoelectricity, followed by a literature review and justification of the choice of the subject. The second chapter puts forward a novel approach to stabilize a disordered CTS polymorph without any chemical alteration through high-energy reactive ball milling. The third chapter deals with the stability of disordered samples under different synthesis and sintering conditions, highlighting the effect of synthesis environment, microstructure, and porosity. The fourth chapter employed a novel, facile, and cost-effective two-step synthesis method (high-energy ball milling combined with spark plasma sintering) to synthesize CTS bulk samples. The two-step synthesis method was able to constrain the CTS grain growth in the nanometric range, revealing the conductive nature of the CTS surfaces. The next chapter explores combining the two-step synthesis method with Ag substitution at the Sn lattice site to improve CTS's thermoelectric performance further. In the final stages of the thesis work, thin film thermoelectric generators were fabricated using CTS and similar chalcogenides, demonstrating power output comparable to existing thermoelectric materials used in the medium temperature range. The final chapter summarizes outlooks and future perspectives stemming from this research work.

Kesterite thin film solar cells are one of the most promising technologies for the future thin film PV market. The term “kesterite” refers to the crystal structure that the Cu2ZnSn(S,Se)4 compound adopts. This thesis discusses the study of the formation of the pure selenide of the kesterite compound Cu2ZnSnSe4 (CZTSe) as an absorber layer. The layers were produced by a 2-stage physical vapour deposition (PVD) of Cu-Zn-Sn precursor films by sputtering followed by a reactive conversion step in the presence of Se. Solar cells have been fabricated with the absorbers produced. The research explored the evolution of phases during the formation of CZTSe and the influence of the absorber composition on its optical and microstructural properties. In addition, the work involved: optimisation of the CZTSe synthesis process, studying the influence of the Se source, the role of temperature of the conversion process, the role of ramping rate and the ambient pressure, and the role of these for maximising device performance. From the study of the evolution of phases it was concluded that CZTSe can be formed from Cu-Zn-Sn precursors over a wide range of temperatures (380-550 oC). The formation of the ternary compound Cu2SnSe3 (CTSe) from Cu-Sn precursors using the same synthesis approach was also demonstrated. Whilst this material was considered unsuitable as a solar PV absorber layer due to its low bandgap, the pure sulphide ternary phase Cu2SnS3 (CTS) was considered more suitable and was synthesised using a single step co-evaporation PVD method. A device with an efficiency of 1.8% demonstrated the possibility of using this earth abundant compound for thin film PV. A combination of X-ray diffraction and Raman spectroscopy studies demonstrated that CZTSe films with very Cu-poor and Zn-rich compositions led to a high population of the beneficial VCu + ZnCu defect clusters, and CZTSe phase domains with a less disordered kesterite type structure. This led to devices with efficiencies over 8% and VOC values greater than those of the current world record CZTSe solar cells. The research of this thesis provides a combination of practical and fundamental knowledge that could become a key towards minimising the efficiency gap between kesterites and their commercialised chalcogenide predecessors: CdTe and Cu(In,Ga)Se2.

Le materiau Cu2SnS3 (CTS) est un semi-conducteur caracterisé par une bande interdite direct et un fort coefficient d'absorption optique dans le domaine du visible. Ces propriétés font de lui un des composes les plus attractifs pour une application photovoltaïque en couches minces. Compare aux technologies concurrentes, le CTS tire ces principaux avantages du nombre et de la nature de ses éléments. Ils sont abondants et non toxiques, une tendance encourageante qui promet de développer une future technologie de photopiles a faible cout et respectueuse de l’environnement. L’objectif de ce travail est de réaliser des dépôts de films minces microstructures de CTS a partir de nanoparticules du même matériau. Pour se faire, un protocole expérimental original a été adopte en associant deux procédés d’élaboration simple : hydrothermal et CVD a courte distance. Cette approche a permis de s’affranchir des procédés conventionnels couteux actuellement employés
The Cu2SnS3 compound (CTS) is a semiconductor characterized by a direct band gap and a high optical absorption coefficient in the visible range. These properties make it one of the most attractive materials for thin-film photovoltaic (PV) applications. Compared to competing technologies, CTS derives its main benefits from the number and nature of its constituent elements. They are abundant and non-toxic. This encouraging trend is propitious for the development of future low cost and environmentally friendly solar cell technology. The aim of our study is to develop CTS thin films from the same nanostructured source material. To this end, we have have developed an original experimental procedure, by combining two simple, low-cost and environmentally friendly processes: Hydrothermal and Short-Range CVD. This approach has made it unnecessary to use the conventional costly processes presently employed

В работе с помощью коллоидального синтеза были получены наноразмерные тетраподы трехкомпонентного соединения Cu2SnSe3. Методами просвечивающей электронной микроскопии, рентгенодифрактометрии, рентгеноспектрального анализа были изучены морфология, структурные свойства и элементный состав, полученных наночастиц. Установлено, что трехмерные частицы имели форму ядра с симметрично расположенными четырьмя выростами - «руками». Рентгено-дифрактометрический анализ показал присутствие в наночастицах с элементным составом Cu1.83Sn0,86Sn3 сфалеритной и вюрцитной фаз.
In work Cu2SnSe3 nanotetrapods using colloidal synthesis were obtained. By transmission electron microscopy, X-ray diffractometry, energy dispersive spectroscopy were studied morphological, structural properties and chemical composition of the obtained ternary chalcogenide zinc (Cu2SnSe3). The nanoparticles had the form of a core with symmetrically arranged 4 "hands". X-ray diffraction analysis showed the presence sphalerite and wurtzite phases in nanoparticles with the elemental composition Cu1,83Sn0,86Sn3

碩士
國立臺南大學
電機工程學系碩博士班
103
In this study, we investigated the ternary I–IV–VI compounds semiconductor layer synthesized by a simple and low-cost solvent-thermal refluxing method follow annealing. The thin films are suitable to be absorber layer of solar cells. At first, we fabricated the varied concentration of Cu-Sn-S precursor ink. After sulfurization, we obtained pure phase of CTS by sulfurizing the Cu-Sn-S precursor of the lower concentration. The CTS thin film is p-type with a carrier concentration of ∼5.23×1017 cm-3, and hole mobility of 14.2 cm2 V−1 s−1, which is suitable to be absorber layer of solar cells. We fabricated the Cu-Sn-Se precursor ink by different reaction time. At the longer reaction time, we obtained pure phase of CTSe. At the shorter reaction time, we obtained Cu2-xSe crystals and unformed Cu-Sn-Se groups. After selenization, the structures of Cu2SnSe3 were destructured and binary CuSe appeared. In contrast, after selenization, the precursors of short reaction time transform into pure Cu2SnSe3. The CTSe thin film is p-type with a carrier concentration of ∼1.9×1017 cm−3, and higher hole mobility of 13.66 cm2 V−1 s−1, which is suitable to be absorber layer of solar cells. In this study, we fabricated the ternary I–IV–VI compounds thin films by a simple and low-cost solvent-thermal refluxing method and and annealing.

碩士
國立臺灣科技大學
材料科學與工程系
103
Due to the energy crisis, we rush into the solar cell research and development. Fulfillment of energy is an issue that is always covered by each of the countries, coupled with the increasing rate of world population growth the energy consumption will continue to increase. Solar cell is one of the best choices, solar cells has been studied for more than fifty years but the last decade has seen the drastic growth in the research and development in the sector and because of that, now we have so many different types of solar cells design with megawatt production capabilities. Modern solar cells design can be fabricated using different materials and can have different structure. Cu2SnSe3 (CTSe) is a potential candidate for absorber materials of solar cells. In this study, we report the effects of doping Mg on the structural, electrical, and optical properties of these CTSe thin films for devolepment of highly efficient solar cells for long term energy production. Thin films of the CTSe and Mg-doped CTSe were sputtered with two different targets of Cu and Sn or Cu-Mg and Sn, respectively , followed by the selenization at 500-600 oC under the Se vapor. The films were characterized by FE-SEM, EDS, XRD, and Hall measurement and other analyses to explore the effects of Mg-doping with different ratios on CTSe thin film. All the thin films CTSe and Mg-doped CTSe were deposited by DC magnetron co-sputtering at room temperature with the powers of 26 W for Cu target and 16 W for Sn target for CTSe thin films and 26 W for Cu-Mg target and 16 W for Sn target for Mg-CTSe for 1hour. A two-step selenization process was executed at 300 oC and holding period of 30 min before reaching to three different selenization temeperatures of 500 oC, 550 oC, and 600 oC. The selenization procedure had been done in Se ambient arisen from SnSe2 pellet. Almost all thin films selenized at 550 oC-selenized films had the composition closed to expected stoichiometry of Cu2SnSe3. The major XRD diffraction peaks appeared at 2θ of 26.8°, 44.8°, 53.2°, 65.5°, and 72.3° which could be attributed to (111), (220), (311), (400), and (331) planes, respectively. All the diffraction peaks of CTSe could be assigned to the crystal planes from standard structure of Cu2SnSe3 (JCPDS No.89-2879). The optical band gaps obtained by extrapolating the linear region of the absorption spectra did not significantly change. The optical absorption studies indicated a direct band gap of 1.18 ~ 1.20 eV. Undoped CTSe and Mg-0.1-CTSe films selenized at 550 oC exhibited p-type conductivity and they were n-type for Mg-0.2-CTSe and Mg-0.3-CTSe. The Hall measurements for carrier concentration and Hall mobility were 2.54×1019 cm−3 and 681 cm2V−1s−1, respectively, for undoped CTSe film, 9.08 ’ 1018 cm-3 and 71 cm2V-1s-1 for Mg-0.1-CTSe, 1.18 ’ 1019cm−3 and 11 cm2V−1s−1 for Mg-0.2-CTSe, and 1.06 ’ 1019cm−3 and 43 cm2V−1s−1 for Mg-0.3-CTSe, after selenization at 550 oC.

碩士
國立臺灣科技大學
材料科技研究所
97
Recently, the research of solar cells is much more attractive and its technological progress is very fast. Although solar cells have reached a good conversion efficiency, high cost has limited their further applications. Lowering the cost with the finding of new materials is necessary. Although there are many CuInSe2 replacements, low-cost Cu2SnSe3 thin films with an energy band gap of 0.7-0.9 eV have not been seriously investigated for the absorption layer of the solar cells. In this study, the effects of the target composition, substrate temperature, annealing temperature, and the Se compensating discs on the sputtered Cu2SnSe3 thin films are discussed. The physical characteristics of the Cu2SnSe3 thin films were invstigated by XRD, FE-SEM, and EDS XRD. Hall measurement and Absorption spectroscopy were used for the electrical and optical properties, respectively. The experimental results shows that the sputtered Cu2SnSe3 thin films deposited at 400oC followed by annealing at 500oC have a better performance. At this condition, the films are p-type and have well crystallized with a large grain size of 1-3 �慆, a direct energy gap of 0.7-0.8 eV, an absorption coefficient of 104 cm-1 before and after annealing, a carrier concentration of 5×1019 cm-3, and the highest carrier mobility of 8~10 cm2V-1s-1.

碩士
國立東華大學
物理學系
105
The effect of Sb doping on the thermoelectric properties including electrical resistivity, thermal conductivity, and Seebeck oefficient of Cu2SnSe3 has been studied in the temperature range of 10 - 400 K. Besides, thermoelectric performance of the Cu2Sn1-xSbxSe3 (0 ≤ x ≤ 0.04) series with different preparation processes, i.e. conventional solid state route and spark plasma sintering (SPS), is compared. For samples prepared by conventional solid state route, electrical resistivity is found to decrease with increase in Sb content up to x = 0.02, then it increases with further increase in x. The Seebeck coefficient for all samples is positive, indicating that the dominant charge carries are holes. The thermal conductivity is found to decrease with increase in Sb concentration, presumably due to point-defect scattering as a result of Sb substitution. The electronic thermal conductivity κe is estimated to be about 1% of the total thermal conductivity, suggesting that the thermal conduction is mainly associated with lattice thermal conductivity κL. The highest value of figure of merit at 400 K is equal to 0.0137 for the sample Cu2Sn0.99Sb0.01Se3 which is about eight times greater than that of the pristine sample. It is observed that electrical resistivity for all the samples prepared by SPS technique is reduced considerably than the samples prepared by solid state reaction method, which is favorable in enhancing ZT because the electrical resistivity should be low for good thermoelectric materials. It is also noted that the Seebeck coefficient for samples prepared by SPS are significantly enhanced in comparison with the samples prepared by solid state reaction method. In particular, Seebeck coefficient of the x = 0.01 sample is about 295 μV/K at 400 K, which is about two times greater than that of the sample prepared by solid state reaction method. In addition, it is clearly seen that thermal conductivity values for samples prepared using SPS method are larger than that of samples prepared using solid state reaction method, demonstrating that SPS could produce denser samples with a better crystallinity. The maximum ZT value reaches 0.046 at 400 K for the Cu2Sn0.96Sb0.04Se3 sample, which is about 18 times greater than the sample prepared by solid state reaction method. In conclusion, it is found that the presently studied Cu2Sn1-xSbxSe3 (0 ≤ x ≤ 0.04) samples prepared by SPS exhibits a better thermoelectric performance than solid state route.

碩士
長庚大學
化工與材料工程學系
104
In this study, the ternary Cu2SnSe3 semiconductor thin films were prepared using the thermal treatment of Cu2SnSe3 particles obtained from solution growth technology. The effects of Cu/Sn molar ratios in samples on the structural, electrical, and optical properties of the samples were investigated. The average particle size of the samples decreased with an increase in [Sn]/[Cu] molar ratio. X-ray diffraction pattern(XRD) and energy dispersive analysis of X-ray(EDAX) show that there were Se vacancies when the annealing temperature is higher than 450°C and the optimal annealing temperature is 410°C. The crystal phase of the films changed from cubic-Cu2Se to cubic-Cu2SnSe3 with an increase in [Sn]/[Cu] molar ratio. The direct energy band gaps of thin films varied from 0.98~1.10eV, respectively, depending on [Sn]/[Cu] molar ratio in samples. From the Hall measurement analysis, the carrier concentration decreased and the resistivity increased with an increase in [Sn]/[Cu] molar ratio in samples. Hall measurement showed the conduction type of samples (A) and (B) were p-type, but samples (C)~(E) were n-type. The flat band potentials of samples were in the range of -0.56～-0.13V(vs. Normal hydrogen electrode, NHE) in the 0.5M K2SO4 solution obtained using Mott-Schottky measurements. The Maximum photoelectrochemical performance of samples reached to 0.24 mA/cm2 at the external potential of +0.4 V(vs. Ag/AgCl) in the 0.5M K2SO4 solution.

Dissertação de Mestrado em Engenharia Física apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
Quaternary Cu2ZnSnSe4 (CZTSe) is a promising semiconductor material for absorber layer in thin lm solar cells due to direct band gap around 1eV and high absorption coe cient (> 104cm1) (7). The highest conversion e - ciency of CZTSe solar cells is above 11% (8). Nevertheless, a low open circuit voltage with respect to the band gap is a common phenomenon in CZTSe photovoltaic devices. A plausible reason for this is a reduction in the e ective band gap due to inhomogeneities in structure, phase, or composition. To gain a detailed knowledge of the in uence of phase inhomogeneities on the performance of solar cells, the understanding of detection limits of conventionally used characterization methods is essential. The aim of this work is to study the sensitivity limits of X-ray di raction and Raman spectroscopy to the presence of two very common secondary phases for Cu2ZnSnSe4{ZnSe and Cu2SnSe3. Polycrystalline powder of two CZTSe samples (slightly Zn-rich) and one Cu2SnSe3 sample have been grown using the solid state reaction method in evacuated silica tubes. Additionally, an industrially produced powder of ZnSe has been used to produce a number of mixtures of corresponding CZTSe with 1%, 2%, 3%, 5%, 10% and 20% of ZnSe or Cu2SnSe3 respectively. The structural characterization of the starting materials as well as of mixtures was carried out by powder X-ray di raction (PXRD) and subsequent Rietveld analysis of the di raction data using the FullProf suite (11). Rietveld re nement of di raction data of the mixtures was performed, paying a special attention to the in uence of amounts of ZnSe and Cu2SnSe3 on the di raction patterns of the mixtures. The amounts of secondary phases determined by Rietveld re nement have been compared with the initial data, determining in this way the detection limits of PXRD for these secondary phases. To study the crystal structure of the synthesized mixtures at the micrometer scale Raman spectroscopy has been employed. In these measurements a 632:8nm laser line was employed and it was found to be e cient for both ZnSe and Cu2SnSe3 phase detection. By performing Raman line scan measurements we evaluated characteristic Raman mode intensities corresponding to the di erent phases and thus are able to estimate the mixture composition.

碩士
國立成功大學
材料科學及工程學系碩博士班
100
In the present study, the synthesis of Cu2SnSe3 (CTSe) and In-doped CTSe (CTISe) nanocrystals by two solvothermal processes as a function of the solvent, the molar ratio of precursors, temperature and time were explored. Meanwhile, the optical and thermoelectric properties of CTSe and CTISe nanocrystals were also studied. On synthesis in an autoclave, the addition of hydrazine to the ethylenediamine solvent speeded up the formation of pure CTSe and CTISe nanocrystals at 190˚C for 48 and 72 h, respectively. The reason can be explained in terms of the dimensional reduction of metal chalcogenides in the solvothermal reaction by hydrazine. However, as compared with the undoped CTSe nanocrystals, the formation rate of CTISe nanocrystals is significantly depressed due to In doping. On synthesis in N2 in the oleylamine solvent, the pure CTSe and CTISe nanocrystals could be acquired at 210˚C for 36 and 60 h, respectively, also revealing that In-doping depressed the growth rate of CTSe nanocrystals. The broader peak at 180 cm-1 in the Raman spectrum of CTISe nanocrystals as compared with that of CTSe nanocrystals indicates that the In-doping induces a change of the chemical bonding in the CTSe lattice. The bandgaps of CTSe and CTISe nanocrystals were determined to be about 1.08 eV by UV-vis spectroscopy, revealing that the In doping had no significant effect on the bandgap of the CTSe crystals.

No
Here we report an investigation of systematic control of crystal phase in the ternary nanocrystal system, dicopper tin triselenide. Optimizing the synthetic parameters allows modulation between nucleation and growth in either the hexagonal or cubic phase. In addition to size controlled single crystals, the particles can be tuned to occur as 1D linear heterostructures or 3D tetrapods with growth in one phase and termination in the alternate.
SFI, IRCSET

碩士
國立虎尾科技大學
材料科學與綠色能源工程研究所
102
In this study, ternary Cu2SnSe3 thin films were synthesized by non-vacuum processes. First of all, Cu, Sn and Se elements with different ratio, were melted in quartz tubes at 1050 oC to form ingots from Cu-poor, stoichiometric to Cu-rich mixtures (Cu/Sn atomic ratio = 1.5, 2.0 and 2.5, respectively). Inks of the mixtures were made using wet-type ball milling, and printed onto a glass substrate to form a precursor film by spin coating. Then, the samples were heated with rapid thermal annealing(RTA) in a furnace at 300 to 550 oC, respectively, for 10 minutes. The compositions of the films were determined by inductively coupled plasma-mass spectrometer (ICP) and energy dispersive spectroscopy (EDS) measurements. Surface and cross-section morphologies were observed by scanning electron microscopy (SEM). The crystal structure of the films was analyzed by X-ray diffraction (XRD) and the band gaps were obtained by Photoluminescence (PLE) measurement. Optical properties were recorded by UV-Vis-NIR spectrometer. Based on the results of the experiments, the thin films (Cu/Sn atomic ratio = 1.5) with sphalerite structure were obtained by RTA 450 oC , 10 minutes. It also showed higher crystallinity with larger grain size, and the band gap was 1.00eV.

碩士
國立成功大學
微電子工程研究所碩博士班
97
This thesis investigated the possible reaction route of quaternary semiconductor Cu2ZnSnSe4 (CZTSe) absorber synthesized by surface Zn diffusion to underneath Copper-Tin-Selenide ternary layer at 500oC. The electrical property of CZTSe was also investigated for the first time. In this thesis, Zn thickness and duration of annealing were optimized to fabricate near stoichiometric CZTSe film. Single phase CZTSe was produced by annealing 300 nm Zn/2.65 um Cu2SnSe3 at 500oC for 1.5 hours. Raman scattering analysis was used to identified the phase transformation from Cu2SnSe3 to CZTSe. It also showed that the synthesized film was single phase CZTSe without ZnSe binary compound. Hall measurement results showed that these films are p-type with low resistivity and high carrier concentration of 1021cm-3. Finally, the insufficient Se ratio problem was resolved by replacing the of Cu-Sn selenization temperature from 450oC to 250oC so as to increase the incorpoaration of Se with Cu and Sn to form CuSe2 and SnSe instead of ternary. CZTSe film with grain size up to 1.5 um and nearly stichiometric ratio was obtained.

Dissertação de Mestrado Integrado em Engenharia Física apresentada à Faculdade de Ciências e Tecnologia
O quaternário Cu2ZnSnSe4 quaternário (CZTSe) é um material semicondutor promissor para camadas de absorção em células solares de filme fino devido ao seu band gap direto com energia por volta de 1 eV e alto coeficiente de absorção maior que 104 cm-1 [6]. A maior eficiência de conversão das células solares CZTSe alcançada até agora é superior a 11,6% [7]. No entanto, um fenómeno preocupante e comum em dispositivos fotovoltaicos com base em CZTSe é uma baixa tensão de circuito aberto em relação à energia de band gap. Uma razão plausível para tal pode ser uma redução no band gap efetivo devido a heterogeneidades na estrutura, fase ou composição na camada de absorção. Para obter um conhecimento detalhado sobre a influência das heterogeneidades de fase no desempenho das células solares, a compreensão dos limites de detecção dos métodos de investigação é essencial. Os limites de sensibilidade dos métodos utilizados convencionalmente, como difração de raios-X e espectroscopia de Raman, foram estudados recentemente [10]. Este trabalho tem com objetivo compreender os reais níveis de sensibilidade de XANES à presença de Cu2SnSe3 e ZnSe em Cu2ZnSnSe4, duas fases secundárias muito comuns para este material. Adicionalmente, foram investigados os efeitos de submeter amostras de CZTSe altamente não-estequiométricas contendo muitas fases secundárias a um segundo processo de recozimento térmico, com foco em mudanças nos seus conteúdos de fases e as composições das fases CZTSe.Para atingir o objetivo principal deste trabalho, foram utilizados dois conjuntos de amostras de pó policristalino. De modo a simular absorvedores CZTSe contendo uma fase secundária, o pó CZTSe monofásico foi misturado com quantidades determinadas de pó de fase secundária – Cu2SnSe3 ou ZnSe monofásicos – para obter uma série de calibração de misturas CZTSe contendo 1%, 2% 3%, 5%, 10% e 20% de fase secundária. Os dois conjuntos de misturas foram preparados em pellets e medidos por XANES em modo de transmissão nas K-edges de Se e Cu. Os dados das medições foram analisados com o programa ATHENA [21] usando um método de fitting por combinação linear (LCF).A caracterização de fase das amostras CZTSe recozidas foi realizada por difração de raios-X, enquanto a análise composicional foi realizada por espectroscopia de raios-X dispersiva de comprimento de onda.Os resultados obtidos mostraram que XANES é capaz de quantificar a fase secundária ZnSe a todas as concentrações dentro de uma pequena barra de erro. Com esta técnica, também foi possível detetar a fase Cu2SnSe3 até uma concentração de 5%. A investigação sobre a influência da estequiometria do standard de CZTSe e a adição de vários standards de fase secundária à análise LCF apresentaram resultados bastante inconclusivos, particularmente com as misturas de ZnSe, mas revelou a necessidade de uma investigação mais aprofundada sobre esses tópicos.Os resultados das técnicas aplicadas às amostras recozidas mostraram que o conteúdo de fases secundárias permaneceu idêntico na maioria das amostras e que a quantidade de fases CZTSe distintas não diminuiu em nenhuma delas, embora a composição destas tenha mudado em relação àquelas anteriormente presentes. No final, determinou-se que o recozimento não teve grandes benefícios no aumento da homogeneidade das amostras.
The quaternary Cu2ZnSnSe4 (CZTSe) is a promising semiconductor material for absorber layers in thin film solar cells due to its direct band gap around 1 eV and high absorption coefficient larger than 104 cm-1 [6]. The highest conversion efficiency of CZTSe solar cells achieved so far is above 11.6% [7]. However, one troubling and common phenomenon in CZTSe-based photovoltaic devices is a low open-circuit voltage with respect to the band gap energy. A plausible reason for this could be a reduction in the effective band gap due to inhomogeneities in structure, phase, or composition in the absorber layer. To gain a detailed knowledge on the influence of phase inhomogeneities on the performance of solar cells, the understanding of detection limits of investigation methods is essential. The sensitivity limits of the conventionally used methods such as X-ray diffraction and Raman spectroscopy were studied recently [10]. This work aims to understand the real sensitivity levels of XANES to the presence of Cu2SnSe3 and ZnSe in Cu2ZnSnSe4, two very common secondary phases for this compound. Additionally, the effects of subjecting highly off-stoichiometric CZTSe samples containing many secondary phases to a second thermal annealing process were investigated, focusing on changes in their phase contents and the compositions of the CZTSe phases.To achieve the main purpose of this work, two sets of polycrystalline powder samples were used. So as to simulate secondary phase-containing CZTSe absorbers, single-phase CZTSe powder was mixed with determined amounts of secondary phase powder – single-phase Cu2SnSe3 or ZnSe – in order to obtain a calibration series of CZTSe mixtures containing 1%, 2%, 3%, 5%, 10% and 20% of secondary phase. The two mixture sets were prepared into pellets and measured by transmission mode XANES at the Se and Cu K-edges. Data from these measurements were analysed with the ATHENA program [21] using a linear combination fitting (LCF) method.The phase characterization of the re-annealed CZTSe samples was carried out by powder X-ray diffraction, while the compositional analysis was performed by wavelength-dispersive X-ray spectroscopy.Results obtained have shown that XANES is capable of quantifying the ZnSe secondary phase at all concentrations within a small error bar. With this technique, it was also possible to detect the Cu2SnSe3 phase down to 5% concentration. Investigation on the influence of the CZTSe standard’s stoichiometry and the addition of various secondary phase standards to the LCF analysis had largely inconclusive results, particularly with the ZnSe mixtures, but revealed the necessity for further investigation on these topics.Results from the techniques applied to the re-annealed samples showed that the secondary phase contents had remained identical in most samples and that the amount of distinct CZTSe phases did not decrease in any of them, although their composition had changed with respect to those previously present. In the end, it was determined that the annealing had no major benefits in increasing the homogeneity of the samples.
Outro - ERASMUS

碩士
國立臺南大學
電機工程學系碩博士班
106
Abstract In this paper, a simple, low-cost non-vacuum solvothermal refluxing method is used to obtain a I-IV-VI ternary compound Cu2SnSe3(CTSe) film after selenization heat treatment. The CTSe film is suitable as an absorber layer for light sensors and thin film solar cells. First, we successfully synthesized a mixed nano ink of Cu2Se and SnSe2 and CuSe and SnSe2 by adding a new organic solvent Polyetheramine(D400) by non-vacuum solvothermal reflux method, and both used a stoichiometric ratio of 2:1:3. The ratio of copper, tin and selenium was obtained by heat treatment by selenization to obtain a ternary single phase Cu2SnSe3(CTSe) film. The former has a selenization temperature of 550°C and the heating time is 5 minutes, while the latter has a selenization temperature of 550°C and a heating time of 15 minutes. Finally, because the quality of the film is not enough for us to make further applications, so we will try to look at the new preparation method to improve the crystallization and compactness of the film in the next chapter. Next, in order to improve the quality of the film, Cu2SnSe3(CTSe) single phase and CuSe and SnSe2 hybrid phase precursor film were successfully prepared by non-vacuum solvothermal refluxing method and centrifugal powders and blade coating. CTSe ternary single phase was obtained by rapid selenization heat treatment under pressure. The best conditions for the two groups are a selenization temperature of 500°C and a heating time of 60 minutes. Finally, compared to the experimental method in the previous chapter, we think this is a way to find an improvement. Although the crystallinity and compactness have a certain degree of improvement in quality, but the quality of the film after selenization may not be very stable, so we can still carry out more tests and compare the operation methods of the blade coating, to continue to do related applications.

碩士
國立臺南大學
電機工程學系碩博士班
105
In this education, we examined the ternary I–IV–VI mixes semiconductor layer synthesized by a humble and low-cost solvent-thermal refluxing method follow annealing. The thin films are appropriate to be absorber layer of solar cells. Cu-containing ternary chalcogenides (Cu2SnSe3) were positively synthesized by stoichiometric amount of the preliminary resources via a simple and suitable solvent-thermal-reflux reaction of copper powder, tin powder with selenium powder in the time variety of 30min-12hr for 150℃、190℃、230℃. In this study, we firstly examine nonvacuum process polyetheramine synthesized Cu2SnSe3 (CTSe) nanoink creation device based on time reliant on phase development and particle nucleation and development. We fabricated the Cu-Sn-Se precursor hybrid nanoink by different reaction time. After selenization, the structures of Cu2SnSe3 were destructured and binary CuSe seemed. In contrast, after selenization, the precursors of short reaction time alter into pure Cu2SnSe3. The CTSe thin film is p-type with a carrier concentration of ∼1.9×1019 cm−3, and higher hole mobility of 13.66 cm2 V−1 s−1, which is suitable to be absorber layer of solar cells. In this study, we fabricated the ternary I–IV–VI compounds thin films by a simple and low-cost solvent-thermal refluxing method and and annealing.

碩士
國立虎尾科技大學
材料科學與綠色能源工程研究所
103
The experiment is investigate on the application of Cu2ZnSn(SSe)4 for solar cell absorber layer materials. First of all, copper, tin, selenium the three elements, prepared by melting into the ternary mixture, and adding a binary synthesis (ZnS)compound to mix, the ink is prepared using wet-ball milling , Cu/Zn+Sn atomic ratio were 0.6、0.8、1、1.5，by spin coating. The precursor layer is placed in RTP furnace, and then heated at the temperature between 300 oC to 500oC,respectively, for 10minutes，prepared Cu2ZnSn(SSe)4 2-3μm thick film.In passing a high purity nitrogen gas under high temperature by diffusion。 The compositions of the films were determined by inductively coupled plasma-mass spectrometer(ICP)measurements，Surface and cross-section morphologies were observed by scanning electron microscopy.The crystal structure of the films was analyzed by X-ray diffraction .Optical properties were recorded by UV-Vis-NIR spectrometer. Based on the results of the experiments, the thin films (Cu/Zn+Sn atomic ratio = 0.8) with Better crystalline were obtained by RTA 500 oC , 10 minutes. It also showed higher crystallinity with larger grain size, and the band gap was 1.44eV.

碩士
國立臺灣科技大學
化學工程系
101
In this study, a quaternary compound semiconductor-copper tin sulfide selenide could be employed as photocathode to produce hydrogen by water splitting due to similar band gap as copper zinc tin sulfide selenide and higher conduction band position than water reduction potential. In addition, nanowire materials own good carrier transport behavior because of quantum confinement effect. Therefore, a solvothermal method was used to synthesize copper tine sulfide selenide nanowire and the band gap modulation was controlled by the ratio of sulfur and selenium in the anion precursors. For copper tine sulfide selenide nanowire synthesis, three stages process and two stages process were used. In three stages process, Cu2-xSeS nanowires were synthesized at first. After that, Cu2-xSeS nanowires were treated by sodium citrate aqueous solution. Because citrate ions could catch copper ion from Cu2-xSeS nanowires, it can transfer into Cusses nanowires which is an unstable phase for the tin incorporation in the next step. However, the morphologies of nanowires could be destroyed when we increased the content of Se. Therefore, a two stages process was employed to discuss the possible for the incorporation of tin element without the sodium citrate treatment. The structural identifications were characterized by Raman and X-ray diffraction.

Thermoelectric (TE) materials directly convert heat energy into electrical energy. The conversion efficiency of the TE devices depends on the performance of the materials. The conversion efficiency of available thermoelectric materials and devices is low. Therefore, the development of new materials for improving thermoelectric device performance is a highly essential. As the performance of the TE materials depends on TE figure of merit [zT=S2P T ] which consist of three material properties such as Seebeck coefficient (S), electrical resistivity ( ) and thermal conductivity ( ). Thermoelectric figure of merit can be improved by either increase of power factor or decreasing of thermal conductivity or by both. In the present thesis, Cu based chalcogenide compounds are chosen for the study of thermoelectric properties because of their complex crystal structure, which leads to lower values of thermal conductivity. Also, the power factor of these materials can be tuned by the partial substitution doping. In the present thesis, Cu based chalcogenide compounds quaternary chalcogenide compound (Cu2ZnSnSe4), ternary compounds (Cu2SnSe3 and Cu2GeSe3) and tetrahedrite materials (Cu12Sb4S13) have been prepared by solid state synthesis. The prepared compounds are characterized by XRD for the phase identification, Raman Spectroscopy used as complementary technique for XRD, SEM for surface morphology and EPMA for the phase purity and elemental composition analysis respectively. For the evaluation of zT, thermoelectric properties of all the samples have been studied by measuring Seebeck coefficient, resistivity and thermal diffusivity. In the chapter 1, a brief introduction about thermoelectricity and its effects is discussed. Thermoelectric materials parameters such as electrical resistivity, Seebeck coefficient and thermal conductivity for different class of materials are mentioned. The selection of thermoelectric materials and the motivation for choosing the Cu based chalcogenide compounds for thermoelectric applications are discussed. In chapter 2, the details of the experiments carried out for Cu based chalcogenide compounds are presented. In chapter 3, the effect on thermoelectric properties by the cation substitution on quaternary chalcogenide compound Cu2+xZnSn1 xSe4 (0, 0.025, 0.05, 0.075, 0.1, 0.125, and 0.15) is studied. The electrical resistivity of all the samples decreases with an increase in Cu content except for Cu21ZnSn09Se4, most likely due to a higher content of the ZnSe. All the samples showed positive Seebeck coefficients indicating that holes are the majority charge carriers. The thermal conductivity of doped samples was higher as compared to Cu2ZnSnSe4 and this may be due to the larger electronic contribution and the presence of the ZnSe phase in the doped samples. The maximum zT = 0.23 at 673 K is obtained for Cu205ZnSn095Se4. In chapter 4, the effect of multi{substitution of Cu21ZnSn1 xInxSe4 (0, 0.05, 0.075, and 0.1) on transport properties were studied. The Rietveld powder X-ray diffraction data accompanied by electron probe microanalysis (EPMA) and Raman spectra of all the samples con firmed the formation of a tetragonal kesterite structure. The electrical resistivity of all the samples exhibits metallic-like behavior. The positive values of the Seebeck coefficient and the Hall coefficient reveal that holes are the majority charge carriers. The co-doping of copper and indium leads to a significant increase of the electrical resistivity and the Seebeck coefficient as a function of temperature above 650 K. The thermal conductivity of all the samples decreases with increasing temperature. Lattice thermal conductivity is not significantly modified as the doping content may infer negligible mass fluctuation scattering for copper zinc and indium tin substitution. Even though, the power factors (S2 ) of indium-doped samples Cu21ZnSn1 xInxSe4 (x=0.05, 0.075) are almost the same, the maximum zT=0.45 at 773 K was obtained for Cu21Zn09Sn0925In0075Se4 due to its smaller value of thermal conductivity. In chapter 5, thermoelectric properties of Zn doped ternary compounds Cu2ZnxSn1 xSe3 (x = 0, 0.025, 0.05, 0.075) were studied. The undoped com\pound showed a monoclinic crystal structure as a major phase, while the doped compounds showed a cubic crystal structure confirmed by powder XRD (X-Ray Diffraction). The electrical resistivity decreased up to the samples with Zn content x=0.05 in Cu2ZnxSn1 xSe3, and slightly increased in the sample Cu2Zn0075Sn0925Se3 . This behavior is consistent with the changes in the carrier concentration confirmed by room temperature Hall coefficient data. Temperature dependent electrical resistivity of all samples showed heavily doped semiconductor behavior. All the samples exhibit positive Seebeck coefficient (S) and Hall coefficient indicating that the majority of the carriers are holes. A linear increase in Seebeck coefficient with increase in temperature indicates the degenerate semiconductor behavior. The total thermal conductivity of the doped samples increased with a higher amount of doping, due to the increase in the carrier contribution. The total and lattice thermal conductivity of all samples decreased with increasing of temperature, which points toward the dominance of phonon scattering at high temperatures. The maximum zT = 0.34 at 723 K is obtained for the sample Cu2SnSe3 due to a low thermal conductivity compared to the doped samples. In chapter 6, thermoelectric properties of Cu2Ge1 xInxSe3 (x = 0, 0.05, 0.1, 0.15) compounds is studied. The powder X-ray diffraction pattern of the undoped sample revealed an orthorhombic phase. The increase in doping content led to the appearance of additional peaks related to cubic and tetragonal phases along with the orthorhombic phase. This may be due to the substitutional disorder created by indium doping. The electrical resistivity ( ) systematically decreased with an increase in doping content, but increased with the temperature indicating a heavily doped semiconductor behavior. A positive Seebeck coefficient (S) of all samples in the entire temperature range reveal holes as predominant charge carriers. Positive Hall coefficient data for the compounds Cu2Ge1 xInxSe3 (x= 0, 0.1) at room temperature (RT) con rm the sign of Seebeck coefficient. The trend of as a function of doping content for the samples Cu2Ge1 xInxSe3 with x = 0 and 0.1 agrees with the measured charge carrier density calculated from Hall data. The total thermal conductivity increased with rising doping content, attributed to an increase in carrier thermal conductivity. The thermal conductivity decreases with increasing temperature, which indicates the dominance of Umklapp phonon scattering at elevated temperatures. The maximum thermoelectric figure of merit (zT) = 0.23 at 723 K was obtained for Cu2In01Ge09Se3. In chapter 7, thermoelectric properties of Cu12 xMn1 xSb4S13 (x = 0, 0.5, 1.0, 1.5, 2.0) samples were studied. The Rietveld powder XRD pattern and Electron Probe Micro Analysis revealed that all the Mn substituted samples showed a single tetrahedrite phase. The electrical resistivity increased with increasing Mn due to substitution of Mn2+ on the Cu1+ site. The positive Seebeck coefficient for all samples indicates that the dominant carriers are holes. Even though the thermal conductivity decreased as a function of increasing Mn, the thermoelectric figure of merit (zT) decreased, because the decrease of the power factor is stronger than the decrease of the thermal conductivity. The maximum zT = 0.76 at 623 K is obtained for Cu12Sb4S13. In chapter 8, the summary and conclusion of the present work is presented.