Electrostatic Potentials at Cu(In,Ga)<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>Se</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>Grain Boundaries: Experiment and Simulations

Schmidt, S.; Abou‐Ras, Daniel; Sadewasser, Sascha; Yin, Wan‐Jian; Feng, Chunbao; Yan, Yanfa

doi:10.1103/physrevlett.109.095506

Cited by 41 publications

(25 citation statements)

References 35 publications

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“…We consequently directly measured the electrostatic potential distribution within MAS grains using OAEH at the nanometer scale . This method has been applied to analyze the electrostatic potential at interfaces, in undoped and Nb‐doped SrTiO 3 bi‐crystals, at grain boundaries in SrTiO 3 and Cu(In,Ga)Se 2 and at Si p ‐ n junctions …”

Section: Resultsmentioning

confidence: 99%

Charge distribution in nano‐scale grains of magnesium aluminate spinel

et al. 2016

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Charge distribution in magnesium aluminate spinel (MAS) results in the formation of a space‐charge region that plays a critical role in assigning functional properties. Significant theoretical advances explaining this phenomenon have been accomplished, even though quantitative experimental support from nano‐scale granular MAS is only indirect. In this work, the electrostatic potential distribution in nano‐scale grains of nonstoichiometric MAS (MgO·0.95Al2O3 and MgO·1.07Al2O3) was measured by off‐axis electron holography (OAEH) and compared to the distribution of cations and defects in this material as measured by electron energy‐loss spectroscopy (EELS). In this manner, we studied the roles of composition, grain size, and applied electric field (EF) on the formation of a space‐charge region. We quantitatively demonstrated that regardless of grain size, the vicinity of MgO·0.95Al2O3 grain boundaries presented an excess of Mg+2 cations, whereas the vicinity of MgO·1.07Al2O3 grain boundaries included an excess of Al+3 cations. The degree of structural disorder (ie, the inversion parameter, i) indicated that as‐synthesized MAS were significantly disordered (i between 0.37 and 0.41), with values decreasing toward equilibrium ordering values following annealing (i between 0.27 and 0.31). The application of an external ~150 V/cm EF during annealing further enhanced lattice ordering (i between 0.16 and 0.19). Such variations in the distribution of cations and defects should determine the space‐charged potential (SCP). However, using these measurements to calculate the SCP was not possible due to the wide range of values reported for formation energies of defects (0.82‐8.78 eV). Consequently, we correlated local ionic ordering with electrostatic potential in nonstoichiometric MAS. The magnitudes of the SCP in both MgO·0.95Al2O3 and MgO·1.07Al2O3 decreased following annealing from −3.4 ± 0.3 V and 2.0 ± 0.2 V to −2.0 ± 0.2 V and 1.6 ± 0.1 V, respectively.

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Section: Resultsmentioning

confidence: 99%

Charge distribution in nano‐scale grains of magnesium aluminate spinel

et al. 2016

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“…By means of inline electron holography, potential wells were detected at Σ3 and Σ9 twin boundaries as well as at dislocations and random grain boundaries . It was found that these potential wells exhibit depths, which increase with decreasing symmetry: –0.2 V, –0.5 V, and –1 V to –3 V for Σ3, Σ9, and random grain boundaries.…”

Section: Changes In Structure and Composition: Atomic Reconstruction mentioning

confidence: 98%

Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se₂ thin films for solar cells – a review

Abou‐Ras

Schmidt

Schäfer

et al. 2016

Physica Rapid Research Ltrs

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The present review gives an overview of the various reports on properties of line and planar defects in Cu(In,Ga)(S,Se)2 thin films for high‐efficiency solar cells. We report results from various analysis techniques applied to characterize these defects at different length scales, which allow for drawing a consistent picture on structural and electronic defect properties. A key finding is atomic reconstruction detected at line and planar defects, which may be one mechanism to reduce excess charge densities and to relax deep‐defect states from midgap to shallow energy levels. On the other hand, nonradiative Shockley–Read–Hall recombination is still enhanced with respect to defect‐free grain interiors, which is correlated with substantial reduction of luminescence intensities. Comparison of the microscopic electrical properties of planar defects in Cu(In,Ga)(S,Se)2 thin films with two‐dimensional device simulations suggest that these defects are one origin of the reduced open‐circuit voltage of the photovoltaic devices. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

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“…13,21 Structural defects such as dislocations and stacking faults were found in CIGSe and Cu 2 ZnSnS 4 films using transmission electron microscopy (TEM). [21][22][23][24][25][26] Yet, no detailed information on the effect of the Cu-poor to Cu-rich transition on the density of planar defects (PDs) is found in the literature. While fascinating insights into annihilation mechanisms of single planar defects in other metallic or compound fcc materials were obtained by time-resolved TEM studies, [27][28][29] real-time in situ TEM in a reactive Cu-Se atmosphere to study defect annihilation in CIGSe does not seem to be feasible.…”

Section: Introductionmentioning

confidence: 99%

Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

Mainz

Sanli

Stange

et al. 2016

Energy Environ. Sci.

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aIn polycrystalline semiconductor absorbers for thin-film solar cells, structural defects may enhance electron-hole recombination and hence lower the resulting energy conversion efficiency. To be able to efficiently design and optimize fabrication processes that result in high-quality materials, knowledge of the nature of structural defects as well as their formation and annihilation during film growth is essential. Here we show that in co-evaporated Cu(In,Ga)Se 2 absorber films the density of defects is strongly influenced by the reaction path and substrate temperature during film growth. A combination of high-resolution electron microscopy, atomic force microscopy, scanning tunneling microscopy, and X-ray diffraction shows that Cu(In,Ga)Se 2 absorber films deposited at low temperature without a Cu-rich stage suffer from a high density of -partially electronically active -planar defects in the {112} planes. Real-time X-ray diffraction Broader contextThe development of thin-film solar cells has been a success story in recent years in terms of record efficiencies in the lab. Single junction solar cells based on compound semiconductor films have reached higher energy-conversion efficiencies than polycrystalline silicon. Despite this success and the prospects of novel applications such as flexible, lightweight solar panels, the market share of thin-film solar modules is stagnating. A major problem of compound thin-film solar cells, such as Cu(In,Ga)Se 2 , is the large gap between lab efficiencies and commercial module efficiencies. A large process parameter space makes trial-and-error optimization a time-consuming and expensive task. Therefore, understanding the underlying atomic-scale physics and chemistry is essential to identify the potential origins of efficiency losses in the transfer from lab-to large-scale fabrication. Even though Cu(In,Ga)Se 2 has been investigated for several decades, there is still a lack of fundamental knowledge of the quality-determining mechanisms during film growth. In this contribution we present results from an international collaboration that provides direct insight into defect formation and annihilation during the fabrication of Cu(In,Ga)Se 2 films. Consequences for process optimization and design are proposed. The presented approach can also be applied to understand other thin-film fabrication processes.

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Electrostatic Potentials at Cu(In,Ga)Se2Grain Boundaries: Experiment and Simulations

Cited by 41 publications

References 35 publications

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se₂ thin films for solar cells – a review

Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

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Electrostatic Potentials at Cu(In,Ga)Se2Grain Boundaries: Experiment and Simulations

Cited by 41 publications

References 35 publications

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Charge distribution in nano‐scale grains of magnesium aluminate spinel

Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se2 thin films for solar cells – a review

Annihilation of structural defects in chalcogenide absorber films for high-efficiency solar cells

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Compositional and electrical properties of line and planar defects in Cu(In,Ga)Se₂ thin films for solar cells – a review