<i>In situ</i> analysis of elemental depth distributions in thin films by combined evaluation of synchrotron x-ray fluorescence and diffraction

Mainz, Roland

doi:10.1063/1.3592288

Cited by 22 publications

(11 citation statements)

References 40 publications

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“…3e) and then abruptly become steeper. Numerical model calculations revealed that this steepening of the Cu-Kα intensity can be explained by Cu 2 Se segregation at the lm surface with a constant growth rate, 19,34 which is consistent with recent observations by real-time ellipsometry. 35 The steepening is more pronounced in detector 2 than in detector 1, because detector 2 has a lower exit angle and hence a higher surface sensitivity than detector 1.…”

Section: Role Of Cu Saturationsupporting

confidence: 76%

Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation

et al. 2015

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In polycrystalline compound semiconductor thin lms, structural defects such as grain boundaries as well as lateral stress can form during lm growth, which may deteriorate their electronic performance and mechanical stability. In Cu-based chalcogenide semiconductors such as Cu(In, Ga)Se2 or Cu2ZnSn(S, Se)4, temporary Cu excess during lm growth leads to improved microstructure such as a reduced grain boundary density, a strategy that has been used for decades for high-eciency chalcopyrite thin lm solar cells. However, the mechanisms responsible for the benecial eect of Cu-excess are yet not fully claried. Here, we investigate the evolution of lateral stress, grain growth and Cu-Se segregation during Cu-Se deposition onto Cu-poor CuInSe2. Real-time x-ray diraction and uorescence analysis with a double-detector setup reveals that sudden stress relaxation occurs shortly prior to Cu-Se segregation at the surface and precisely coincides with domain growth and change of texture. Numerical reaction-diusion modeling provides an explanation for the observed delay of Cu-Se segregation. Our results show that partial recrystallization of the lm can be already reached without the necessity of an overall Cu-rich lm composition and thus suggest a new synthesis route for the fabrication of high-quality chalcopyrite absorber lms.Co-evaporation of Cu(In, Ga)Se 2 (CIGSe) lms -used as absorber layer in thin lm solar cells with world record energy conversion eciencies 1,2 -features a puzzling peculiarity: For the nal lm, a Cu-poor composi-is required to obtain highest eciencies; however, during deposition, the lm composition is changed from an initially Cu-poor composition to an intermediate Cu-rich composition and nally changed back to a Cu-poor composition. The composition modications during lm deposition are realized by varying the Cu and In+Ga evaporation uxes. Two crucial ndings point out the importance of the Cu-poor → Cu-rich transition: First, highest eciencies are only achieved if an intermediate Cu-rich lm composition was reached during lm deposition. 3 Second, a three-stage process with a Cu-poor → Cu-rich → Cu-poor sequence leads to higher eciencies than a two-stage process with only a Cu-rich → Cu-poor sequence. 46 Thus, it seems that the key challenge in understanding the success of the three-stage process over the two stage-process is -besides the adjustment of an ideal Ga gradient -the identication of the reactions and their driving forces acting during the Cu-poor → Cu-rich transition.While the eect of the Cu-poor → Cu-rich transition on structural and morphological changes in CIGSe lms such as grain growth 710 as well as on electronic properties of the material 3,11 has been thoroughly investigated in the past decade, the physical mechanisms and driving forces of these changes are not fully understood. Reduction of grain boundary (GB) energies or defect densities were proposed as possible driving forces for grain growth; 79 however, no attention has so far been paid to the potential role of stress energy for the mic...

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Section: Role Of Cu Saturationsupporting

confidence: 76%

Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation

et al. 2015

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“…Additionally, X-ray fluorescence (XRF) signalseven of heavy elementsare measured simultaneously to the Bragg reflexes. These XRF signals provide information about material adsorption and desorption as well as elemental distributions [15,16].…”

Section: Energy Dispersive X-ray Diffraction (Edxrd)mentioning

confidence: 99%

“…Since the number of fluorescence signals that are measured under one or more fixed angles is limited, the depth distributions have to be parameterized such that the number of parameters does not exceed the number of measured fluorescence signals. It can be demonstrated that a simple parameterization (where the knowledge of phase formation gained from the simultaneously measured Bragg reflexes are taken as additional constrains) can be used to obtain in-situ depth distributions by a quantitative analysis of the fluorescence signals [16]. Figure 13.12 presents a series of depth distributions during a CuInS 2 synthesis process.…”

Section: Energy Dispersive X-ray Diffraction (Edxrd)mentioning

confidence: 99%

X‐Ray and Neutron Diffraction on Materials for Thin‐Film Solar Cells

Schorr

Stephan

Törndahl

et al. 2011

Advanced Characterization Techniques for Thin Film Solar Cells

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In order to understand natural and artificially produced materials, a detailed understanding of their crystal structures is required. This information is a basis for research in physics, chemistry, biology, and materials science. Among the various experimental methods, neutron and X-ray (photon) scattering have become key techniques of choice. Both techniques are complementary. In X-ray scattering, it is almost exclusively the electrons in atoms which contribute to the scattering, whereas neutrons interact with the atomic nuclei. This has an important consequence: the response of neutrons from light atoms (such as hydrogen or oxygen) is much higher than for X-rays, and neutrons easily distinguish atoms of comparable (or even equal) atomic number (see Figure 13.1). Due to the fact that neutrons interact with atoms via nuclear rather than electrical forces and nuclear forces are very short-range (of the order of a few fermis, i.e., 10 À15 m), the cross section for such an interaction is very small. The size of a scattering center (nucleus) is typically 10 5 times smaller than the distance between such centers. As a consequence, neutrons can travel large distances through most materials without being scattered or absorbed. Thus, neutrons penetrate matter much more deeply than X-rays.While neutron scattering provides insights into the crystal structure with high resolution, X-ray scattering has the advantage that (due to a larger scattering cross section) measurement durations are usually much shorter, compared with neutron scattering. Additionally, lab-scale X-ray sources are broadly available. Diffraction of X-Rays and Neutron by MatterMost of all inorganic, solid materials can be described as crystalline. When X-rays or neutrons interact with a crystalline substance, coherent elastic scattering may occur which is also termed diffraction.

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“…the formation mechanism) using various diffraction methods, but there has been very limited research on the electronic structure of these materials. 20,[29][30][31] There is a lack of information on the composition and bonding of the NCs, including the Cu/In ratio as well as the use of MPP as a capping ligand for CIS. MPP removes the need for high temperature annealing necessary in the case of the insulating ligands typically involved in the synthesis of the NCs.…”

Section: Introductionmentioning

confidence: 99%

Assessing the Band Structure of CuInS₂ Nanocrystals and Their Bonding with the Capping Ligand

et al. 2015

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CuInS 2 (CIS) nanocrystals (NCs) prepared optimally via a one-pot solvothermal method exhibit a high absorption coefficient and an ideal band gap for solar cell light-absorbing materials. We find that the initial Cu/In ratio in the synthesis determines the final composition of CIS and this further dictates the photoelectrochemical performance of the CIS NC films. X-ray absorption near edge spectroscopy excludes the presence of a secondary phase and suggests a difference in surface band bending and in ligand-CIS interaction. These findings will aid optimizing the design of CIS NC films to achieve the highest possible photovoltaic efficiency.

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In situ analysis of elemental depth distributions in thin films by combined evaluation of synchrotron x-ray fluorescence and diffraction

Cited by 22 publications

References 40 publications

Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation

Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation

X‐Ray and Neutron Diffraction on Materials for Thin‐Film Solar Cells

Assessing the Band Structure of CuInS₂ Nanocrystals and Their Bonding with the Capping Ligand

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In situ analysis of elemental depth distributions in thin films by combined evaluation of synchrotron x-ray fluorescence and diffraction

Cited by 22 publications

References 40 publications

Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation

Sudden stress relaxation in compound semiconductor thin films triggered by secondary phase segregation

X‐Ray and Neutron Diffraction on Materials for Thin‐Film Solar Cells

Assessing the Band Structure of CuInS2 Nanocrystals and Their Bonding with the Capping Ligand

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Assessing the Band Structure of CuInS₂ Nanocrystals and Their Bonding with the Capping Ligand