Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

Parvan, V.; Mızrak, Alpay Koray; Majumdar, Isheta; Ümsür, Bünyamin; Calvet, Wolfram; Greiner, D.; Kaufmann, Christian A.; Dittrich, Thomas; Avancini, Enrico; Lauermann, Iver

doi:10.1016/j.apsusc.2018.03.014

Cited by 5 publications

(1 citation statement)

References 28 publications

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“…Therefore, the traditional fixed capacitor with a buffer will remain important especially for separate and relatively fast modulated SPV measurements on common photoactive materials, such as TiO 2 , BiVO 4 , or Cu 2 O. Furthermore, in comparison with SPV measurements with a fixed capacitor in ultrahigh vacuum, [30] treated surfaces are not in mechanical contact with an insulator for the nonconventional approach what is a big advantage for its future application in ultrahigh vacuum.…”

Section: Discussionmentioning

confidence: 99%

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Dittrich

Fengler

Nickel

2021

Physica Status Solidi (a)

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Semiconductors with ultrawide bandgap (E g ), such as Ga 2 O 3 , can be applied, for example, in power electronics and optoelectronic devices due to their high breakdown voltage and transparency, respectively. [1][2][3] Aside this, semiconductors with ultrawide bandgap are also of increasing interest for solar energy conversion. For example, Ga 2 O 3 layers can serve as passivation, transparent ohmic contact or charge-selective contact layers as shown in solar cells based on Cu(In,Ga)Se 2 , [4] c-Si, [5] or Cu 2 O [6] absorbers, respectively. Furthermore, Ga 2 O 3 is of great interest for photocatalytic water splitting. As very few examples, the role of copper and chromia-based cocatalysts on Ga 2 O 3 , [7] of mixed-phase junctions based on β-Ga 2 O 3 /α-Ga 2 O 3 , [8,9] of zinc and lead dopants in Ga 2 O 3 [10] or of nickel oxide cocatalysts on α-Ga 2 O 3 [11] for photocatalytic activity and photocatalytic water splitting were investigated empirically and by firstprinciple studies, respectively.Electronic states in the bandgap are crucial for the operation of electronic, optoelectronic, solar cell, and photocatalytic devices. Therefore, the characterization of electronic states and the study of their interactions is decisive for the engineering of electronic states and the further development of devices. Energy levels of deep defect states in Ga 2 O 3 were obtained using deeplevel transient spectroscopy (DLTS) [12,13] and Hall effect measurements at high temperatures. [14] Several transition energies were measured by cathodoluminescence spectroscopy. [15] However, reliable data about defect states and electronic transitions in Ga 2 O 3 are sparse and the characterization of electronic transitions and their impact on electronic properties of semiconductors with ultrawide bandgap over the entire E g is often challenging.Surface photovoltage (SPV) techniques provide universal tools for the highly sensitive analysis and investigation of electronic states in semiconductors. [16,17] Recently, for example, transitions and charge transfer processes were studied in c-Si/TiO 2 and CuBi 2 O 4 heterojunctions by transient [18] and modulated [19] SPV spectroscopy, respectively, and the bulk photovoltaic effect has been shown for excitation from defect states in carbon-doped GaN. [20] Incidentally, one SPV spectrum has been shown for Ga 2 O 3 in the work of Gao et al., [15] but in our opinion, the signal-to-noise ratio was insufficient to extract energy levels in a reliable manner.Fast and robust SPV measurements are carried out in the fixed capacitor arrangement [21] for achieving short resolution times (below 1 ns, [22] transient measurements) or high sensitivity (range of 100 nV, [23] modulated measurements). In the fixed capacitor arrangement, an electrode based on a transparent conducting oxide (TCO) and an insulating foil between the sample and the electrode are used for forming the measurement capacitor for capacitive out-coupling of SPV signals. However, optical absorption in the TCO electrode and in the insulating fo...

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Section: Discussionmentioning

confidence: 99%

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Dittrich

Fengler

Nickel

2021

Physica Status Solidi (a)

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Effect of Ga Variation on the Bulk and Grain‐Boundary Properties of Cu(In,Ga)Se₂ Absorbers in Thin‐Film Solar Cells and Their Impacts on Open‐Circuit Voltage Losses

Thomas,

Witte,

Hariskos

et al. 2024

Progress in Photovoltaics

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Polycrystalline widegap Cu(In,Ga)Se2 (CIGSe) absorbers for top cells in photovoltaic tandem devices can be synthesized via [Ga]/([Ga] + [In]) (GGI) ratios of > 0.5. However, the power conversion efficiencies of such high‐GGI devices are smaller than those of the record cells with GGI < 0.5. In the present work, the effects of the GGI ratio on various CIGSe material properties were studied and correlated with the radiative and nonradiative open‐circuit voltage (VOC) deficits of the thin‐film solar cells. Average grain sizes, grain boundary (GB) recombination velocities, fluctuations in luminescence energy distribution, barrier heights at GBs, effective electron lifetimes, and Urbach energies were investigated in five solar cells with GGI ratios from 0.13 to 0.83. It was found that the GGI variation affects GB recombination velocities, fluctuations in spatial luminescence distributions, the average grain size, the electron lifetime, and the Urbach energy. In contrast, the detected ranges of barrier heights at GBs are independent of the GGI ratio. Mainly Ga/In gradients give rise to substantial radiative VOC losses in all solar cells. Nonradiative VOC deficits are dominant especially for solar cells with GGI > 0.5, which can be attributed to low bulk lifetimes and enhanced recombination at GBs in CIGSe absorbers in this compositional range.

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Effect of Na from soda-lime glass substrate and as post-deposition on Cu(In,Ga)Se2 absorbers: A photoelectron spectroscopy study in ultra-high vacuum

Majumdar

Parvan

Greiner

et al. 2020

Applied Surface Science

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Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

Cited by 5 publications

References 28 publications

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Effect of Ga Variation on the Bulk and Grain‐Boundary Properties of Cu(In,Ga)Se₂ Absorbers in Thin‐Film Solar Cells and Their Impacts on Open‐Circuit Voltage Losses

Effect of Na from soda-lime glass substrate and as post-deposition on Cu(In,Ga)Se2 absorbers: A photoelectron spectroscopy study in ultra-high vacuum

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Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

Cited by 5 publications

References 28 publications

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Surface Photovoltage Spectroscopy over Wide Time Domains for Semiconductors with Ultrawide Bandgap: Example of Gallium Oxide

Effect of Ga Variation on the Bulk and Grain‐Boundary Properties of Cu(In,Ga)Se2 Absorbers in Thin‐Film Solar Cells and Their Impacts on Open‐Circuit Voltage Losses

Effect of Na from soda-lime glass substrate and as post-deposition on Cu(In,Ga)Se2 absorbers: A photoelectron spectroscopy study in ultra-high vacuum

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Effect of Ga Variation on the Bulk and Grain‐Boundary Properties of Cu(In,Ga)Se₂ Absorbers in Thin‐Film Solar Cells and Their Impacts on Open‐Circuit Voltage Losses