Native point defects in CuIn1−xGaxSe2: hybrid density functional calculations predict the origin of p- and n-type conductivity

Bekaert, J; Saniz, R.; Partoens, B.; Lamoen, D.

doi:10.1039/c4cp02870h

Cited by 45 publications

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“…9 In contrast, Baekert et al predicted a shallow donor level for these antisites. 10 Electrical measurements based on photo-induced current transient spectroscopy support the assumption of deep intrinsic defect levels acting as recombination centers for electrons. In Ref.…”

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confidence: 99%

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Spindler

Regesch

Siebentritt

2016

Applied Physics Letters

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Recent defect calculations suggest that the open circuit voltage of CuGaSe2 solar cells can be limited by deep intrinsic electron traps by GaCu antisites and their complexes with Cu-vacancies. To gain experimental evidence, two radiative defect transitions at 1.10 eV and 1.24 eV are characterized by steady-state photoluminescence on epitaxial-grown CuGaSe2 thin films. Cu-rich samples are studied, since they show highest crystal quality, exciton luminescence, and no potential fluctuations. Variations of the laser intensity and temperature dependent measurements suggest that emission occurs from two deep donor-like levels into the same shallow acceptor. At 10 K, power-law exponents of 1 (low excitation regime) and 1/2 (high excitation regime) are observed identically for both transitions. The theory and a fitting function for the double power law is derived. It is concluded that the acceptor becomes saturated by excess carriers which changes the exponent of all transitions. Activation energies determined from the temperature quenching depend on the excitation level and show unexpected values of 600 meV and higher. The thermal activation of non-radiative processes can explain the distortion of the ionization energies. Both the deep levels play a major role as radiative and non-radiative recombination centers for electrons and can be detrimental for photovoltaic applications.

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confidence: 99%

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Spindler

Regesch

Siebentritt

2016

Applied Physics Letters

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“…Supercells constructed both from the 16-atom tetragonal unit cell [lattice vectors (a,0,0), (0,a,0), and (0,0,c), c ≈ 2a] [9,12,13] and from the 8-atom triclinic primitive cell [lattice vectors (a,0,0), (0,a,0), and d = (a/2,a/2,c), c ∼ a, |d| ∼ 1.22a] have been employed in the previous studies. [10,11] Various possible supercells with their properties are listed in Table 4.…”

Section: Supercell Shape and Sizementioning

confidence: 99%

“…[6] A plethora of studies concerning defects in CuInSe 2 and CuGaSe 2 has been published over the last two decades. [7][8][9][10][11][12][13] The most recent DFT investigations have employed hybrid functionals, which can overcome the energy band gap problem plaguing the older studies and can thus also provide information about the defect level positions within the band gap. [9][10][11][12][13] The results of different calculations agree well with respect to general trends in formation energies of the most important defects, such as the copper vacancy (V Cu ), indium antisite on copper place (In Cu ), and copper interstitial (Cu int ).…”

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confidence: 99%

First‐Principles Modeling of Point Defects and Complexes in Thin‐Film Solar‐Cell Absorber CuInSe₂

Malitckaya

Komsa

Havu

et al. 2017

Adv Elect Materials

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as the composition of the sample changes from Cu-rich to Cu-poor, so that in the Cupoor samples only one peak is detected. Although only the Cu-poor material is important for actual devices Cu-rich samples give indispensable information for defect identification.First-principles calculations based on the density functional theory (DFT) can be used to obtain important, complementary information about point defects such as formation energies and charge transition levels. [6] A plethora of studies concerning defects in CuInSe 2 and CuGaSe 2 has been published over the last two decades. [7][8][9][10][11][12][13] The most recent DFT investigations have employed hybrid functionals, which can overcome the energy band gap problem plaguing the older studies and can thus also provide information about the defect level positions within the band gap. [9][10][11][12][13] The results of different calculations agree well with respect to general trends in formation energies of the most important defects, such as the copper vacancy (V Cu ), indium antisite on copper place (In Cu ), and copper interstitial (Cu int ). However, the results differ in some important cases. For instance, there are clearly different values for the ionization levels within the band gap for the copper antisite on the indium place (Cu In ) and indium vacancy (V In ). Based on the formation energy calculations, V Cu and Cu In are abundant acceptors, and are most probably responsible for some of the above-mentioned PL peaks, but it is unclear whether any native defect can be responsible for the third acceptor level.One important goal of the present work was to gain a perspective on the present unsatisfactory situation in modeling point defects in CIGSe and to approach the ultimate accuracy by which DFT is able to predict the properties of bulk crystalline materials. [14] First we carried out a detailed benchmarking of the first-principles computational scheme used. We checked effects due to the supercell size and shape, as well as those of the finite-size supercell correction scheme. We used also two very different implementations of the first-principles DFT method, which differ in describing valence-core electron interaction and electron wave functions (see below). After finding the computational parameters yielding accurate results, we calculated formation energies and charge transition levels for different acceptor candidates in CuInSe 2 . By carefully considering the relevant chemical potential limits, we were able to draw conclusions about the abundances of different defects. In addition to simple native defects, we have also considered a set of complexes formed by them. Our paper is organized as follows.

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“…In particular, we assume that Cd—or Zn in the case of devices with Zn(O,S) buffer layer—diffuses into the absorber and occupies sites on the Cu lattice. This is predicted to form a donor level in CIGS when Cd occupies a copper site (Cd Cu ) and which would additionally reduce the concentration of copper vacancies (V Cu ) as dominant acceptor state in CIGS …”

Section: Impact Of Deep Trap Levels On Experimental Apparent Dopant Pmentioning

confidence: 99%

Can we see defects in capacitance measurements of thin‐film solar cells?

Werner

Babbe

Elanzeery

et al. 2019

Progress in Photovoltaics

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Thermal admittance spectroscopy and capacitance‐voltage measurements are well established techniques to study recombination‐active deep defect levels and determine the shallow dopant concentration in photovoltaic absorbers. Applied to thin‐film solar cells or any device stack consisting of multiple layers, interpretation of these capacitance‐based techniques is ambiguous at best. We demonstrate how to assess electrical measurements of thin‐film devices and develop a range of criteria that allow to estimate whether deep defects could consistently explain a given capacitance measurement. We show that a broad parameter space, achieved by exploiting bias voltage, time, and illumination as additional experimental parameters in admittance spectroscopy, helps to distinguish between deep defects and capacitive contributions from transport barriers or additional layers in the device stack. On the example of Cu(In,Ga)Se2 thin‐film solar cells, we show that slow trap states are indeed present but cannot be resolved in typical admittance spectra. We explain the common N1 signature by the presence of a capacitive barrier layer and show that the shallow net dopant concentration is not distributed uniformly within the depth of the absorber.

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Native point defects in CuIn_1−xGa_xSe₂: hybrid density functional calculations predict the origin of p- and n-type conductivity

Abstract: Starting from first-principles calculations, many experimental observations such as photoluminescence spectra, charge carrier densities and freeze-out can be explained.

Cited by 45 publications

References 50 publications

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

First‐Principles Modeling of Point Defects and Complexes in Thin‐Film Solar‐Cell Absorber CuInSe₂

Can we see defects in capacitance measurements of thin‐film solar cells?

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Native point defects in CuIn1−xGaxSe2: hybrid density functional calculations predict the origin of p- and n-type conductivity

Abstract: Starting from first-principles calculations, many experimental observations such as photoluminescence spectra, charge carrier densities and freeze-out can be explained.

Cited by 45 publications

References 50 publications

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

Revisiting radiative deep-level transitions in CuGaSe2 by photoluminescence

First‐Principles Modeling of Point Defects and Complexes in Thin‐Film Solar‐Cell Absorber CuInSe2

Can we see defects in capacitance measurements of thin‐film solar cells?

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Native point defects in CuIn_1−xGa_xSe₂: hybrid density functional calculations predict the origin of p- and n-type conductivity

First‐Principles Modeling of Point Defects and Complexes in Thin‐Film Solar‐Cell Absorber CuInSe₂