Direct Insight into Grain Boundary Reconstruction in Polycrystalline<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Cu</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mi>In</mml:mi><mml:mo>,</mml:mo><mml:mi>Ga</mml:mi><mml:mo stretchy="false">)</mml:mo><mml:msub><mml:mi>Se</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>with Atomic Resolution

Abou‐Ras, Daniel; Schaffer, Bernhard; Schaffer, Miroslava; Schmidt, S.; Caballero, R.; Unold, Thomas

doi:10.1103/physrevlett.108.075502

Cited by 94 publications

(74 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In previous studies, the occurrence of cation redistribution at random GBs was unambiguously demonstrated, including clear evidence for regions with Cu enrichment and In depletion. 16,17 However, contrary to the present report, these Cu-rich/In-poor boundary regions did not exhibit any clear crystallinity, i.e., no highly ordered secondary phase was observed at those boundaries. The presence of a remnant Cu 2-x Se fully ordered phase at GBs and within grains appears therefore to be a rare occurrence (within the limited statistics of atomic-resolution STEM observation).…”

contrasting

confidence: 55%

Evidence for Cu2–xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

Sanli

Ramasse

Mainz

et al. 2017

Applied Physics Letters

View full text Add to dashboard Cite

Cu(In,Ga)Se2 (CIGS)-based solar cells reach high power-conversion efficiencies of above 22%. In this work, a three-stage co-evaporation method was used for their fabrication. During the growth stages, the stoichiometry of the absorbers changes from Cu-poor ([Cu]/([In] + [Ga]) < 1) to Cu-rich ([Cu]/([In] + [Ga]) > 1) and finally becomes Cu-poor again when the growth process is completed. It is known that, according to the Cu-In-Ga-Se phase diagram, a Cu-rich growth leads to the presence of Cu2–xSe (x = 0–0.25), which is assumed to assist in recrystallization, grain growth, and defect annihilation in the CIGS layer. So far, Cu2–xSe precipitates with spatial extensions on the order of 10–100 nm have been detected only in Cu-rich CIGS layers. In the present work, we report Cu2–xSe platelets with widths of only a few atomic planes at grain boundaries and as inclusions within grains in a polycrystalline, Cu-poor CIGS layer, as evidenced by high-resolution scanning transmission electron microscopy (STEM). The chemistry of the Cu–Se secondary phase was analyzed by electron energy-loss spectroscopy, and STEM image simulation confirmed the identification of the detected phase. These results represent additional experimental evidence for the proposed topotactical growth model for Cu–Se–assisted CIGS thin-film formation under Cu-rich conditions.

show abstract

contrasting

confidence: 55%

Evidence for Cu2–xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

Sanli

Ramasse

Mainz

et al. 2017

Applied Physics Letters

View full text Add to dashboard Cite

show abstract

“…S3 in SM 22 ). Due to a reduced density at GBs, 27,28 grain growth, i.e. reduction of GB area, generally leads to a material densication.…”

Section: B Correlation Between Strain Relaxation and Grain Growthmentioning

confidence: 99%

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

et al. 2015

View full text Add to dashboard Cite

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...

show abstract

“…When soda-lime glass is used as substrates, even further point defects related to impurities such as Na, O, and K, which diffuse from the glass substrate into the Cu(In,Ga) Se 2 thin films, contribute to the grain-boundary compositions. 35 The complex scenario of the compositional and optoelectronic properties of random grain boundaries in Cu(In,Ga)Se 2 thin films is difficult to be translated into a corresponding energy-band diagram and eventually into a two-or three-dimensional device simulation, which ultimately would give direct insight into how (random) grain bound- aries affect the device performance. Corresponding work is currently in progress.…”

Section: Ebsd Combined With Other Scanning Microscopy Techniquesmentioning

confidence: 99%

“…Indeed, compositional changes are found in Cu(In,Ga)Se 2 thin films within regions around random grain boundaries that have widths of smaller than 1 nm. 34 This is, the atomic planes of neighboring grains that meet at random grain boundaries in Cu(In,Ga)Se 2 thin films are considered reconstructed. It has been found 34,35 that the changes in composition and thus the reconstruction is always different for different (random) grain boundaries, even in identical Cu(In,Ga)Se 2 thin films.…”

Section: Ebsd Combined With Other Scanning Microscopy Techniquesmentioning

confidence: 99%

Electron Backscatter Diffraction: An Important Tool for Analyses of Structure–Property Relationships in Thin-Film Solar Cells

Abou‐Ras

Kavalakkatt

Nichterwitz

et al. 2013

JOM

View full text Add to dashboard Cite

The present work gives an overview of the application of electron backscatter diffraction (EBSD) in the field of thin-film solar cells, which consist of stacks of polycrystalline layers on various rigid or flexible substrates. EBSD provides access to grain-size and local-orientation distributions, film textures, and grain-boundary types. By evaluation of the EBSD patterns within individual grains of the polycrystalline solar cell layers, microstrain distributions also can be obtained. These microstructural properties are of considerable interest for research and development of thin-film solar cells. Moreover, EBSD may be performed three-dimensionally, by alternating slicing of cross sections in a focused ion-beam machine and EBSD acquisition. To relate the microstructural properties to the electrical properties of individual layers as well as to the device performances of corresponding solar cells, EBSD can be combined with electron-beam-induced current and cathodoluminescence measurements and with various scanning-probe microscopy methods such as Kelvin-probe force, scanning spreading resistance, or scanning capacitance microscopy on identical specimen positions. Together with standard device characterization of thin-film solar cells, these scanning microscopy measurements provide the means for extensive analysis of structure-property relationships in solar-cell stacks with polycrystalline layers.

show abstract

Direct Insight into Grain Boundary Reconstruction in PolycrystallineCu(In,Ga)Se2with Atomic Resolution

Cited by 94 publications

References 32 publications

Evidence for Cu2–xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

Evidence for Cu2–xSe platelets at grain boundaries and within grains in Cu(In,Ga)Se2 thin films

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

Electron Backscatter Diffraction: An Important Tool for Analyses of Structure–Property Relationships in Thin-Film Solar Cells

Contact Info

Product

Resources

About