Luận án tiến sĩ kỹ thuật hóa học green and low cost preparation of cigse thin fi

Thesis Green and low-cost preparation of CIGSe thin film by a nanocrystals ink based spin-coating method Graduate School of Yeungnam University School of Chemical Engineering Major in Chemical Engineering Le Thi Thuy Trang Advisor: Prof. Chinho Park Co-advisor: Prof. JaeHong Kim February 2020 i Ph. Thesis Green and low-cost preparation of CIGSe thin film by a nanocrystals ink based spin-coating method Advisor: Prof.

Chinho Park Co-advisor: Prof. JaeHong Kim Presented as Ph. Thesis February 2020 Graduate School of Yeungnam University School of Chemical Engineering Major in Chemical Engineering Le Thi Thuy Trang iii Acknowledgements I woud like to express my deep gratitude to my advisor, Professor Chinho Park at the School of chemical engineering. He has provided me the invaluable contributions in the research work by various profitable discussions.

His devoted instructions have been my sources of inspiration during Ph. periods, and have given me the great encouragement to fulfill both the research and writing of this thesis. I deeply thank to Professor JaeHong Kim, who has supported me to complete this Ph. My special thanks also go to Dr.

Vasu and Dr. Nguyen for their valuable comments and suggestions in my research. I am thankful to the IMSL lab’s members who have ever helped me many things. I will remember for their trust and friendship.

Your sentiments toward me are quite precious. I thank to my family for giving me a wider perspective on things, unlimited forbearance, and the time deprived from them. Last, I gratefully acknowledge Yeungnam university and BK 21 program because of their supports. December, 2019 Le Thi Thuy Trang iv Abstract This thesis presents our efforts that aim towards a green and low cost prodedure to fabricate CIGSe thin films which would be used as absorber layers for the thin film solar cell industry.

So, an ―ink‖ solution based process, using spin-coating technique, followed by annealing in selenium environment with different temperature programs was utilized to prepare CIGSe thin film. Firstly, CIGSe nanoparticles were synthesized using NaBH4 containing green solvent – ethanol by a sonochemical method. The effect of the ultrasonification time intervals on the synthesis was investigated in the range of 2-5 hr, 5 hr was found to be the most suitable time to obtain the expected CuIn0. The as-synthesized CIGSe nanoparticles possessed a tetragonal structure with quasi-spherical shape, and the targeted Cu(In0.

A new reaction scheme is proposed to explain the role of NaBH4 in the plausible reaction paths. The non-toxic solvent used in the synthesis with no additional heating makes the developed method cheaper and ―greener‖ than the previously reported methods. Next, three different solvents: 2-propanol, 2-methoxyethanol, and their 2:1 mixture (v/v ratio) were investigated as a dispersion medium for the as-synthesized CIGSe nanocrystals to form a stable ink solution. The last one – mixture of 2-propanol : 2-methoxyethanol = 2 : 1 (v/v) – was found to be the most suitable.

Furthermore, the influences of various annealing modes on the CIGSe grain size and density in the resulting film were also studied. The as-prepared CIGSe thin film was around 1 µm thick, possessed a tetragonal structure, and the band gap energy was estimated about ~ 1. The newly developed cheaper and ―greener‖ non-vacuum process was applied successfully from the nanocrystals synthesis to the formation of ―ink‖ solution, and produced v high quality thin films, which opens a new route to the cost-competitive commercialization of CIGSe thin film solar cells. vi Contents Acknowledgements.

v List of figures. viii Chapter 1: Literature Overview. The material system of Cu(In,Ga)Se2 quaternary. Introduction of the structural property.

Optical and electrical properties. Overview of solar cell. The story of solar cell. The operating principle of solar cell.

Thin film deposition techniques. The vacuum method. Chemical vapor deposition (CVD). The non-vacuum method.

The nanoparticles based method. Direct solution based process. Physical methods for characterizing solids. 18 Chapter 2: Green and low-cost synthesis of CIGSe nanoparticles using ethanol as a solvent by a sonochemical method - a new approach.

Results and discussion. 34 Chapter 3: The formation of CIGSe thin film by a nanocrystals ink based spin-coating method. Results and discussion. 57 List of puplications.

70 vii List of figures Chapter 1 Fig.1: The unit cell of the chalcopyrite lattice structure a) CuInSe2, b) Cu(In,Ga)Se2.2: The working of a silicon solar cell.3: The structure of a dye sensitized solar cells.4: Mechanism of dye sensitized solar cell.5: Basic structure or Organic Solar Cell. 1 6: The operating principle of solar cell. 1 7: Schematic of evaporation system. 1 8: Schematic illustration of different coevaporation recipes .9: Schematic of sputtering system .10: Schematic of chemical vapor deposition system .11: Schematic illustration of X-ray generation system.

1 12: (a) Section through an X-ray tube. (b) An X-ray emission spectrum.13: Basic components of a monochromatic XPS system .14: Schematic illustration of a raman spectroscopy system.15: Schematic illustration of scanning electron microscopy system.16: Schematic illustration of Scanning electron microscopy system.17: Block diagram of DTA.18: Schematic illustration of differential scanning calorimetry system. 30 viii Chapter 2 Fig.1: XRD patterns of the CIGSe nanoparticles synthesized with difference ultrasonification time.2: SEM images of CIGSe NPs with ultrasonification time of 2 hr (a), 3.3: Raman spectra of as-prepared CuIn0.3Se2 NPs with ultrasonification time of 5 hr.4: a) XPS survey spectrum and Cu 2p (b), In 3d (c), Ga 2p (d) , and Se 3d (e ) core-level spectrum of as-synthesized CuIn0.5: TEM images of CIGSe nanoparticles with ultrasonification time of 5 hr before (a) and after (b) annealed at 500 oC.6: XRD pattern of CuIn0.3Se2 NPs before and after annealed at 500 oC .7: Absorption spectrum (a) and plot of (αhν)2 versus photon energy hν (b) of the annealed CuIn0.1: The images of colloidal solutions with different dispersion mediums: 2-propanol (a), 2- methoxyethanol (b) and solvent mixture of 2-propanol and 2-methoxyethanol (c) after being kept in 1 month. 3 2: The images of the spin coated films by 2-propanol solvent based ink solution (a), and solvent mixture based ink solution (b).

3 3: Cross-section SEM image of CIGSe thin film with the first annealing mode. 3 4: Cross-section SEM image of CIGSe thin film with the second annealing mode. 3 5: Cross-section SEM image of CIGSe thin film with the third annealing mode. 3 6: Surface SEM image of CIGSe thin film with the third annealing mode.

3 7: XRD pattern of CIGSe thin film after being annealed with the third annealing mode.8: Plot of (αhν)2 versus photon energy hν of CIGSe thin film after being annealed with the third annealing mode. 55 x Chapter 1: Literature Overview 1. The material system of Cu(In,Ga)Se2 quaternary CuInxGa1-xSe2 (CIGSe) quaternary is a p-type semiconductor material which is a member of the I-III-VI2 chalcopyrites family [1]. It has been known as an effective light-absorbing layer for thin film solar cell industry, and CIGSe thin film solar cells were first studied at the Bell laboratories in 1975.

Much efforts have been done on CICSe solar cells, therefore the efficiency of CIGSe solar cells have reached up to 23. Introduction of the structural property. The basis for the structure of CIGSe quaternary is the structure of CISe ternary. Some indium atoms in unit cell of CISe ternary are replaced by gallium atoms to form unit cell of CIGSe [1].1: The unit cell of the chalcopyrite lattice structure a) CuInSe2, b) Cu(In,Ga)Se2 [3].

CIGSe crystals have the tetragonal chalcopyrite lattice structure which drived from the cubic structure of the group IV semiconductor. The unit cell is corresponds to two stacked zincblende unit cells, where copper, indium and gallium atoms are regularly ordered. The lattice parameters of CuInxGa1-xSe2 are a=b= 5.696, value of c depend on value x composition of Ga element [4]. Optical and electrical properties Optical properties CIGSe semiconductors possess high optical absorbtion coefficient α > 105 cm-1, and relatively low direct band gap energy value in the range 1.7 eV, resulting from the hybridization of Cu d-orbitals and Se p-orbitals in the valence bands [5,6].

The band gap energy of CuIn1-xGaxSe2 compounds depend on the Ga/Ga+In concentration ratio, but also by the Cu content. The optical band gap energy of CuInSe2 is about 1. when In atoms are gradually substituted by gallium atoms, the band gap can be increase to 1.68 eV, which is the optical band gap energy of CuGaSe2 [1]. The band gap energies of the CuIn1-xGaxSe2 quaternary with different compositions from x= 0 to 1 are calculated based on an empirical ―bowing equation‖ [7,8]: Eg= 1.167x(1-x) (1) Where the so-called optical bowing coefficient is 0.

Electrical properties The CuIn1-xGaxSe2 absorber layer is a p-type semiconductor with hole concentration about 1016 - 1018 cm-3 at room temperature. The hole mobilities have been obtained values in the range of 15-150 cm2/Vs with single crystals and values of 5-50 cm2/Vs with polycrystalline films [9,10]. Overview of solar cell 1. The story of solar cell 2 In 1839, a French physicist-Alexander Edmond Becquerel discovered the technology directly producing electricity from the solar energy [11].

This was the beginning of the solar cell technology-which open a new gate for the renewable energy technology. Solar cells are often divided into three main caregories which are called generations up to recent years: - The first generation: Monocrystalline silicon (mono c-Si), polycrystalline silicon (poly c-Si) and armophous silicon cells. - The second generation: amorphous silicon (a-Si), CdTe and CuInS/CIGS. - The third generation: DSSCs, Perovskite and organic The first generation The first silicon solar cell with an efficiency of 6% was studied at Bell laboratories and reported by Chapin, Fuller and Pearson in 1954 [12].

One year later, the first commercial solar cells with 2% efficient were produced by Hoffman Electronics corporation using wafers of silicon (monocrystalline silicon). The following success of this technology was mostly founded on the further development of the Czochalski method in the 1940s enabling the production of high purity silicon [13], leading to the efficiency of these solar cells currently reaching to 26. However, the cost of fabricating monocrystalline silicon solar cells are high because of the purification process of bulk. Mandelkorn created n-on-p silicon solar cells which were better suited for space with more resistance to radiation damage at U.

Signal Corps Laboratories, and these cells were applied to a space satellite ― Vanguard 1‖ – a first solar powered satellite launched at this year with a 0.1W, 100 cm2 solar panel [15]. 3 Different from monocrystalline silicon solar cells, the solar cells made from polycrystalline silicon or amorphous silicon are much cheaper because they are much less pure than monocrystalline silicon, therefore the way slicon made is easier and simpler. However, the highest efficient solar cell made from polycrystalline silicon is recorded of 22.3% [14], lower monocrystalline solar cell.2 shows structure of a silicon solar cell. A silicon solar cell typically is a sandwich of two layers : the first layer is a positive layer ( p-type silicon ) which usually made by doping silicon with boron to form extra holes in the lattice.

The second layer is a negative layer ( n-type silicon ) which usually made by doping silicon with phosphorus to gain extra electrons in the lattice.2: The working of a silicon solar cell [16]. Some limitations of this generation : Silicon possesses an indirect band gap with a low absorption coefficient, so it is not a ideal material for a light conversion. Besides, the silicon absorber layers require a high purity and a thickness up to around 200 µm, therefore the cost of fabrication is high and the product is less visual aesthetic. The second generation 4 The second generation solar cells were studied with the purpose of reducing limitations of the first generation solar cells mentioned above.

The advantage of this generation is that Semiconductor materials used in this generation possess direct band gap.