References of "Weiss, Thomas 50003320"
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See detailPhotoluminescence assessment of materials for solar cell absorbers
Siebentritt, Susanne UL; Rau, Uwe; Gharabeiki, Sevan UL et al

in Faraday Discussions (2022)

Absolute photoluminescence measurements present a tool to predict the quality of photovoltaic absorber materials before finishing the solar cells. Quasi Fermi level splitting predicts the maximal open ... [more ▼]

Absolute photoluminescence measurements present a tool to predict the quality of photovoltaic absorber materials before finishing the solar cells. Quasi Fermi level splitting predicts the maximal open circuit voltage. However, various methods to extract quasi Fermi level splitting are plagued by systematic errors in the range of 10–20 meV. It is important to differentiate between the radiative loss and the shift of the emission maximum. They are not the same and when using the emission maximum as the “radiative” band gap to extract the quasi Fermi level splitting from the radiative efficiency, the quasi Fermi level splitting is 10 to 40 meV too low for a typical broadening of the emission spectrum. However, radiative efficiency presents an ideal tool to compare different materials without determining the quasi Fermi level splitting. For comparison with the open circuit voltage, a fit of the high energy slope to generalised Planck’s law gives more reliable results if the fitted temperature, i.e. the slope of the high energy part, is close to the actual measurement temperature. Generalised Planck’s law also allows the extraction of a non-absolute absorptance spectrum, which enables a comparison between the emission maximum energy and the absorption edge. We discuss the errors and the indications when they are negligible and when not. [less ▲]

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See detailNear surface defects: Cause of deficit between internal and external open-circuit voltage in solar cells
Sood, Mohit UL; Urbanaik, Aleksander; Kameni Boumenou, Christian UL et al

in Progress in Photovoltaics (2021)

Interface recombination in a complex multilayered thin-film solar structure causes a disparity between the internal open-circuit voltage (VOC,in), measured by photoluminescence, and the external open ... [more ▼]

Interface recombination in a complex multilayered thin-film solar structure causes a disparity between the internal open-circuit voltage (VOC,in), measured by photoluminescence, and the external open-circuit voltage (VOC,ex), that is, a VOC deficit. Aspirations to reach higher VOC,ex values require a comprehensive knowledge of the connection between VOC deficit and interface recombination. Here, a near-surface defect model is developed for copper indium di-selenide solar cells grown under Cu-excess conditions. These cell show the typical signatures of interface recombination: a strong disparity between VOC,in and VOC,ex, and extrapolation of the temperature dependent q·VOC,ex to a value below the bandgap energy. Yet, these cells do not suffer from reduced interface bandgap or from Fermi-level pinning. The model presented is based on experimental analysis of admittance and deep-level transient spectroscopy, which show the signature of an acceptor defect. Numerical simulations using the near-surface defects model show the signatures of interface recombination without the need for a reduced interface bandgap or Fermi-level pinning. These findings demonstrate that the VOC,in measurements alone can be inconclusive and might conceal the information on interface recombination pathways, establishing the need for complementary techniques like temperature dependent current–voltage measurements to identify the cause of interface recombination in the devices. [less ▲]

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See detailHow photoluminescence can predict the efficiency of solar cells
Siebentritt, Susanne UL; Weiss, Thomas UL; Sood, Mohit UL et al

in JPhys Materials (2021)

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See detailHow band tail recombination influences the open-circuit voltage of solar cells.
Wolter, Max UL; Carron, Romain; Avancini, Enrico et al

in Progress in Photovoltaics (2021)

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See detailHeavy Alkali Treatment of Cu(In,Ga)Se2 Solar Cells: Surface versus Bulk effects
Siebentritt, Susanne UL; Avancini, Enrico; Bär, Marcus et al

in Advanced Energy Materials (2020)

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See detailBulk and surface recombination properties in thin film semiconductors with different surface treatments from timeresolved photoluminescence measurements
Weiss, Thomas UL; Bissig, Benjamin; Feurer, Thomas et al

in Scientific Reports (2019), 9

The knowledge of minority carrier lifetime of a semiconductor is important for the assessment of its quality and design of electronic devices. Time-resolved photoluminescence (TRPL) measurements offer the ... [more ▼]

The knowledge of minority carrier lifetime of a semiconductor is important for the assessment of its quality and design of electronic devices. Time-resolved photoluminescence (TRPL) measurements offer the possibility to extract effective lifetimes in the nanosecond range. However, it is difficult to discriminate between surface and bulk recombination and consequently the bulk properties of the semiconductor cannot be estimated reliably. Here we present an approach to constrain systematically the bulk and surface recombination parameters in semiconducting layers and reduces to finding the roots of a mathematical function. This method disentangles the bulk and surface recombination based on TRPL decay times of samples with different surface preparations. The technique is exemplarily applied to a CuInSe2 and a back-graded Cu(In,Ga)Se2 compound semiconductor, and upper and lower bounds for the recombination parameters and the mobility are obtained. Sets of calculated parameters are extracted and used as input for simulations of photoluminescence transients, yielding a good match to experimental data and validating the effectiveness of the methodology. A script for the simulation of TRPL transients is provided. [less ▲]

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See detailTime-resolved photoluminescence on double graded Cu(In,Ga)Se2 – Impact of front surface recombination and its temperature dependence
Weiss, Thomas UL; Carron, Romain; Wolter, Max UL et al

in Science and Technology of Advanced Materials (2019), 20

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See detailPost-deposition treatment of Cu2ZnSnSe4 with alkalis
Rey, Germain UL; Babbe, Finn UL; Weiss, Thomas UL et al

in Thin Solid Films (2016), 633

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor ... [more ▼]

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor (from 0.58 to 0.61 and 0.62), open-circuit voltage (Voc) (from 314 mV to 337 mV and 325 mV) and short-circuit current density (from 35.3 mA⋅cm −2 to 38.3 mA⋅cm −2 and 38.6 mA⋅cm −2). Voc improvement was higher for solar cells with NaF treatment due to an increase in radiative efficiency at room temperature and shallower defect activation energy as determined by photoluminescence (PL) and temperature dependent admittance spectroscopy, respectively. In the case of KF treatment, red-shift of the PL, higher band tail density of state and donor activation energy deeper in the band gap were limiting further improvement of the Voc compared to NaF treatment. [less ▲]

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See detailImpact of annealing on electrical properties of Cu2ZnSnSe4 absorber layers
Weiss, Thomas UL; Redinger, Alex UL; Rey, Germain UL et al

in Journal of Applied Physics (2016), 120

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See detailOrdering kesterite improves solar cells:A low temperature post-deposition annealing study
Rey, Germain UL; Weiss, Thomas UL; Sendler, Jan UL et al

in Solar Energy Materials & Solar Cells (2016), 151

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See detailELECTRICAL CHARACTERIZATION OF KESTERITE THIN FILM ABSORBERS AND SOLAR CELLS
Weiss, Thomas UL

Doctoral thesis (2015)

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See detailWhat is the band gap of kesterite?
Siebentritt, Susanne UL; Rey, Germain UL; Finger, Ashley UL et al

in Solar Energy Materials & Solar Cells (2015)

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See detailHighly conductive ZnO films with high near infrared transparency
Hala, Matej UL; Fujii, Shohei; Redinger, Alex UL et al

in Progress in Photovoltaics (2015)

We present an approach for deposition of highly conductive nominally undoped ZnO films that are suitable for the n-type window of low band gap solar cells. We demonstrate that low-voltage radio frequency ... [more ▼]

We present an approach for deposition of highly conductive nominally undoped ZnO films that are suitable for the n-type window of low band gap solar cells. We demonstrate that low-voltage radio frequency (RF) biasing of growing ZnO films during their deposition by non-reactive sputtering makes them as conductive as when doped by aluminium (ρ≤1·10−3Ω cm). The films prepared with additional RF biasing possess lower free-carrier concentration and higher free-carrier mobility than Al-doped ZnO (AZO) films of the same resistivity, which results in a substantially higher transparency in the near infrared region (NIR). Furthermore, these films exhibit good ambient stability and lower high-temperature stability than the AZO films of the same thickness. We also present the characteristics of Cu(InGa)Se2, CuInSe2 and Cu2ZnSnSe4-based solar cells prepared with the transparent window bilayer formed of the isolating and conductive ZnO films and compare them to their counterparts with a standard ZnO/AZO bilayer. We show that the solar cells with nominally undoped ZnO as their transparent conductive oxide layer exhibit an improved quantum efficiency for λ > 900 nm, which leads to a higher short circuit current density JSC. This aspect is specifically beneficial in preparation of the Cu2ZnSnSe4 solar cells with band gap down to 0.85 eV; our champion device reached a JSC of nearly 39 mAcm−2, an open circuit voltage of 378 mV, and a power conversion efficiency of 8.4 %. [less ▲]

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See detailDetection of a MoSe2 secondary phase layer in CZTSe by spectroscopic ellipsometry
Demircio glu, Ozden; Mousel, Marina UL; Redinger, Alex UL et al

in JOURNAL OF APPLIED PHYSICS (2015), 118

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See detailThe band gap of Cu2ZnSnSe4: Effect of order-disorder
Rey, Germain UL; Redinger, Alex UL; Sendler, Jan UL et al

in Applied Physics Letters (2014), 105

Detailed reference viewed: 261 (21 UL)