Concentration of defects responsible for persistent photoconductivity in Cu(In,Ga)Se2: Dependence on material composition

Igalson, M.; Maciaszek, M.; Macielak, K.; Czudek, Aniela; Edoff, Marika; Barreau, Nicolas

doi:10.1016/j.tsf.2018.11.038

Cited by 6 publications

(9 citation statements)

References 12 publications

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“…Recently, it was reported that the Na content of the sample has an influence on the density of metastable defects. [ 19,37 ] However, the samples investigated here show no correlation of the diode factor with the integral Na or K content of the sample (Figure S12e,f, Supporting Information).…”

Section: Discussionmentioning

confidence: 89%

“…Light soaking induces a metastably increased net acceptor density in the CIGS absorber layer. [17][18][19][20][21] To measure the increased net acceptor density without relaxation during the measurement, the sample was cooled down to low temperatures, while the illumination was kept on. At set-point temperature, the illumination was switched off and the capacitance-voltage curve was measured under dark conditions at an AC amplitude of 30 mV and a probing frequency of 100 kHz.…”

Section: Methodsmentioning

confidence: 99%

“…CIGS absorber layers generally show metastable behavior, e.g., the doping density and conductivity increase persistently after minority‐carrier injection. [ 17–21 ] The behavior is often assigned to the V Se –V Cu defect complex. [ 22 ] Although the increased acceptor density (i.e., hole quasi‐Fermi level closer to the valence band) has been studied for more than 25 years, [ 23 ] the influence of these metastabilities on the diode factor of the bare absorber (measured optically) and of the solar cell (measured electrically) has not been considered.…”

Section: Introductionmentioning

confidence: 99%

“…CIGS absorber layers generally show metastable behavior, e.g., the doping density and conductivity increase persistently after minority-carrier injection. [17][18][19][20][21] The behavior is often assigned to the V Se -V Cu DOI: 10.1002/solr.202100063 Thin-film Cu(In,Ga)Se 2 solar cells reach power conversion efficiencies exceeding 23% and nonradiative recombination in the bulk is reported to limit device performance. The diode factor has not received much attention, although it limits the fill factor, and therefore the efficiency, for state-of-the-art solar cells.…”

Section: Introductionmentioning

confidence: 99%

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Understanding Performance Limitations of Cu(In,Ga)Se₂ Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

et al. 2021

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Thin‐film Cu(In,Ga)Se2 solar cells reach power conversion efficiencies exceeding 23% and nonradiative recombination in the bulk is reported to limit device performance. The diode factor has not received much attention, although it limits the fill factor, and therefore the efficiency, for state‐of‐the‐art solar cells. Herein, the diode factor of Cu(In,Ga)Se2 absorbers, measured by photoluminescence spectroscopy, and of solar cells, measured by current–voltage and capacitance–voltage characteristics, are compared, supported by simulations using rate equations of generation and recombination. It is found that the diode factor is already increased in the neutral zone of the absorber due to metastable defects, such as the VSe–VCu defect found in Cu(In,Ga)Se2, because of an increased net acceptor density upon minority‐carrier injection. The metastable and persistent increase of the net acceptor density has a detrimental effect on the device performance. Diode factors of 1 and efficiencies exceeding 24% are expected when, in current state‐of‐the‐art Cu(In,Ga)Se2 solar cells, the formation of metastable defects is suppressed.

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Section: Discussionmentioning

confidence: 89%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Understanding Performance Limitations of Cu(In,Ga)Se₂ Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

et al. 2021

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“…10 However, to our knowledge, there have been fewer experimental studies linking the electronic properties of ACIGS with defect-induced metastability. 12 Here, we probe the influence of environmental stress (dark-heat exposure at 85°C for 1000 h and/or light-soaking under simulated 1 sun AM1.5G illumination for 24 h) on the device performance and charge carrier dynamics in penternary ACIGS absorbers. Through control of the selenization conditions prior to absorber growth and the application of a suite of experimental techniques, we correlate the observed changes to the ACIGS trap/ defect properties.…”

Section: Journal Of Applied Physicsmentioning

confidence: 99%

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se2 absorber materials

Ferguson

Farshchi²,

Paul

et al. 2020

Journal of Applied Physics

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Using a combination of optical and electrical measurements, we develop a model for metastable defects in Ag-alloyed Cu(In,Ga)Se 2 , one of the leading thin film photovoltaic materials. By controlling the pre-selenization conditions of the back contact prior to the growth of polycrystalline (Ag,Cu)(In,Ga)Se 2 absorbers and subsequently exposing them to various stresses (light soaking and dark-heat), we explore the nature and role of metastable defects on the electro-optical and photovoltaic performance of high-efficiency solar cell materials and devices. Positron annihilation spectroscopy indicates that dark-heat exposure results in an increase in the concentration of the selenium-copper divacancy complex (V Se -V Cu ), attributed to depassivation of donor defects. Deep-level optical spectroscopy finds a corresponding increase of a defect at E v + 0.98 eV, and deep-level transient spectroscopy suggests that this increase is accompanied by a decrease in the concentration of mid-bandgap recombination centers. Time-resolved photoluminescence excitation spectroscopy data are consistent with the presence of the V Se -V Cu divacancy complex, which may act as a shallow trap for the minority carriers. Light-soaking experiments are consistent with the V Se -V Cu optical cycle proposed by Lany and Zunger, resulting in the conversion of shallow traps into recombination states that limit the effective minority carrier recombination time (and the associated carrier diffusion length) and an increase in the doping density that limits carrier extraction in photovoltaic devices.

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The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se₂ Solar Cells

Pearson

Keller

Stolt

et al. 2022

Physica Status Solidi (b)

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Cu(In,Ga)Se 2 (CIGS) is an established thin-film photovoltaic material, with record cells reaching efficiencies of 22.6% [1] (or 23.4% with sulfur inclusion). [2] There are still significant improvements to be made, however. The best-performing cells have bandgaps in the region of 1.0-1.2 eV but the optimum value for a single-junction solar cell is 1.34 eV. [3] It would also be advantageous to fabricate high-efficiency widegap CIGS devices to enable the material's use as a top cell in a tandem/multijunction device. To achieve high tandem efficiencies (in the two-terminal configuration), it is estimated that bandgaps of 1.6 and 0.9 eV would be required for top and bottom cells, respectively (or 1.91, 1.37, and 0.93 eV, for the top, intermediate, and bottom cells in a triplejunction device). [4] Near-maximum theoretical efficiency can be attained for top cells with bandgaps in the region 1.4-1.9 eV in a four-terminal tandem configuration. [5] Furthermore, the increased output voltages and reduced currents of widegap devices allow solar modules with reduced resistive losses and less dead area in monolithic series connections to be manufactured. By increasing the ratio of Ga to In in the material (referred to henceforth as the GGI, [Ga]/([Ga] þ [In])), the bandgap is also increased, primarily through an energetic increase in the conduction band minimum. However, the open-circuit voltage (V OC ) does not increase linearly with the bandgap. [6,7] Currently it seems that the optimal GGI lies in the range of 0.2-0.3 with values in excess of this upper bound leading to deterioration in device performance. [7][8][9] There are multiple suspected causes for the negative impact of high GGI ratios, including the formation of an unfavorable conduction band offset between the CIGS absorber and cadmium-sulfide (CdS) buffer layer; [10,11] Cu enrichment of grain boundaries (acting either as a region of high recombination or as highly conductive shunt pathways); [12,13] tetragonal distortion of the lattice; [14] or the increase in the energetic depth and density of malign defects. [9,[15][16][17] The incorporation of silver into CIGS, substituting some of the copper atoms, is expected to be beneficial, improving the conduction band offset between the silveralloyed CIGS (ACIGS) and the commonly used CdS buffer layer. [18] Silver incorporation in CIGS is also observed to increase grain size [19] and reduce the melting point of the alloy, which is expected to reduce the density of defects in the material. [20][21][22] With a clear motivation to investigate the incorporation of Ag into CIGS and the realization of high-performance widegap CIGS-based devices, we produced a large series of ACIGS cells, spanning a wide range of compositions. [23] From this work, a compositional window of interest was identified with GGI in the range of 0.66-0.79 and a silver-to-silver-and-copper (AAC) ratio of 0.47-0.67. The upper limit of AAC was chosen to reduce the amount of ordered vacancy compounds (OVCs), forming at the rear of the absorber layer, as ...

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Concentration of defects responsible for persistent photoconductivity in Cu(In,Ga)Se2: Dependence on material composition

Cited by 6 publications

References 12 publications

Understanding Performance Limitations of Cu(In,Ga)Se₂ Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

Understanding Performance Limitations of Cu(In,Ga)Se₂ Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se2 absorber materials

The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se₂ Solar Cells

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Concentration of defects responsible for persistent photoconductivity in Cu(In,Ga)Se2: Dependence on material composition

Cited by 6 publications

References 12 publications

Understanding Performance Limitations of Cu(In,Ga)Se2 Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

Understanding Performance Limitations of Cu(In,Ga)Se2 Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

Defect-mediated metastability and carrier lifetimes in polycrystalline (Ag,Cu)(In,Ga)Se2 absorber materials

The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se2 Solar Cells

Contact Info

Product

Resources

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Understanding Performance Limitations of Cu(In,Ga)Se₂ Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

Understanding Performance Limitations of Cu(In,Ga)Se₂ Solar Cells due to Metastable Defects—A Route toward Higher Efficiencies

The Effect of Absorber Stoichiometry on the Stability of Widegap (Ag,Cu)(In,Ga)Se₂ Solar Cells