Photoluminescence assessment of materials for solar cell absorbers

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 ▲]

Diode Factor in Solar Cells with Metastable Defects and Back Contact Recombination

in Adv. Energy Mater (2022)

Near surface defects: Cause of deficit between internal and external open-circuit voltage in solar cells

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 ▲]

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

in Solar RRL (2021)

How photoluminescence can predict the efficiency of solar cells

in JPhys Materials (2021)

Heavy Alkali Treatment of Cu(In,Ga)Se2 Solar Cells: Surface versus Bulk effects

in Advanced Energy Materials (2020)

Bulk and surface recombination properties in thin film semiconductors with different surface treatments from timeresolved photoluminescence measurements

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 ▲]

Alkali treatments of Cu(In,Ga)Se2 thin‐film absorbers and their impact on transport barriers

in Progress in Photovoltaics (2018)

Impact of annealing on electrical properties of Cu2ZnSnSe4 absorber layers

in Journal of Applied Physics (2016), 120

ELECTRICAL CHARACTERIZATION OF KESTERITE THIN FILM ABSORBERS AND SOLAR CELLS

Doctoral thesis (2015)