We develop a band-fluctuations model which describes the absorption coefficient in the fundamental absorption region for direct and indirect electronic transitions in disordered semiconductor materials. The model accurately describes both the Urbach tail and absorption edge regions observed in such materials near the mobility edge in a single equation with only three fitting parameters. An asymptotic analysis leads to the universally observed exponential tail below the bandgap energy and to the absorption edge model at zero Kelvin above it, for either direct or indirect electronic transitions. The latter feature allows the discrimination between the absorption edge and absorption tails, thus yielding more accurate bandgap values when fitting optical absorption data. We examine the general character of the model using a dimensionless joint density of states formalism with a quantitative a...

To obtain an adequate luminescent emission, a significant effort must be made to find a suitable host material. An interesting and highly efficient method is a combinatorial approach, which allows high velocity screening of a wider range of properties. In the present work, a compositional gradient-based, thin-film library of -AlOxNy:Yb3+ has been prepared by radio frequency co-sputtering from two targets. The ytterbium concentration range spreads from 0.9 to 4.2 at. % and the oxygen to nitrogen ratio from 0.6 to 3.6. Using different annealing temperatures, the activation energy of the rare earth ions and activation mechanisms can be evaluated. Finally, optimal elemental compositions in the investigated range are proposed.

This research was funded by the Research Management Office (DGI) of the Pontificia Universidad Católica del Perú (PUCP). The authors have been supported by the PUCP under the PhD scholarship program Huiracocha (J A Guerra) and by the National Council of Science and Technology (CONCYTEC) under the scholarships granted to the PUCP (J R Angulo and J Llamoza). The author would like to thank Prof Dr H P Strunk, F Benz and Dr Y Weng of the University of Stuttgart for the TEM measurements.

We report on the optical bandgap engineering of sputtered hydrogenated amorphous silicon carbide (a-SiC:H) thin films under different hydrogen dilution conditions during the deposition process and after post-deposition annealing treatments. The Tauc-gap and Urbach energy are calculated from ultraviolet-visible optical transmittance measurements. Additionally, the effect of the thermal annealing temperature on the hydrogen out-diffusion is assessed through infra-red absorption spectroscopy. A new model for the optical absorption of amorphous semiconductors is presented and employed to determine the bandgap as well as the Urbach energy from a single fit of the absorption coefficient. This model allowed the discrimination of the Urbach tail from the Tauc region without any external bias. Finally, the effect of the hydrogen dilution on the band-edge and the Urbach focus is discussed.

This research was funded by the Research Management Office (DGI) of the Pontificia Universidad Católica del Perú (PUCP). The authors have been supported by the PUCP under the PhD scholarship program Huiracocha (J.A. Guerra), the “Programa de repatriación” (J.A. Töfflinger), the Master scholarship (L.M. Montañez and K. Tucto) from CONCYTEC and the “Círculo de investigación” from CONCYTEC. The authors would like to thank Prof. Dr. A. R. Zanatta (IFSC-USP, Brazil) for providing access to his lab in order to perform the PL measurements and Prof. Dr. H. P. Strunk (University of Stuttgart, Germany) for helping us with the PLE measurements.

This study presents for the first time the spectral impact on the performance of different photovoltaic (PV) technologies in Lima, Peru. We experimentally monitored the spectral distributions over one year (March 2019–February 2020). The average photon energy (APE) is calculated as a representative parameter to evaluate the spectral distributions. The spectral mismatch factor (MM) enables an estimation of the spectral gains of distinct PV technologies: amorphous silicon (a-Si), perovskite, cadmium telluride (CdTe), multicrystalline silicon (multi-Si), monocrystalline silicon (mono-Si) and copper indium gallium selenide with two distinct band-gaps (CIGS-1 and CIGS-2). We found that the annual APE has a value of 1.923 eV, indicating that the spectrum is shifted to shorter wavelengths. In contrast to studies performed in other locations, the spectral distribution shows relatively small mo...

We demonstrate that the modulated surface photovoltage spectroscopy (modulated SPS) technique can be applied to investigate interface states in the bandgap, i.e. interface passivation, of crystalline silicon coated with a downshift layer such as hydrogenated aluminum nitride with embedded terbium ions by suppressing straylight with a cut-off filter. Different hydrogen contents influence the surface photovoltage spectra at photon energies below the bandgap of crystalline silicon. Modulated SPS reveals that at higher hydrogen content there is a lower signal and, thus, a lower density of surface defect states. Our experiments show that modulated SPS can become a powerful tool for characterizing defect states at interfaces which cannot be easily studied by other methods. © 2021 Published under licence by IOP Publishing Ltd.

This article presents the benefits of two simple analytical models for estimating the outdoor performance of three different photovoltaic technologies in Lima, Peru. The Osterwald and the constant fill factor models are implemented to estimate the maximum power delivered by three photovoltaic module technologies: aluminum back surface field, heterojunction with intrinsic thin-layer and amorphous/microcrystalline thin-film tandem. A 12-months experimental campaign is carried out through measurements of current-voltage curves, irradiance and module temperature. The results show that both models overestimate the modelled power when compared to the measured one. In order to correct the maximum power predicted by both models, a correction factor is introduced. This correction factor allows us to estimate losses and a respective effective nominal power to minimize the prediction error on a mon...

Monitoring photovoltaic (PV) systems is necessary to assure their proper functioning. Mostly automated data acquisition systems (DAQ) are used for this purpose. Obtained data from DAQ are important for analysing the energy behavior of PV systems with any anomalies that may appear. It helps investors to realize economic calculations which use to estimate the return on investment. The article aims to present an open-source system that allows the acquisition and reliable recording of meteorological parameters that influence in the energy production of PV installations. The measurement processes were tested by different methods in order to comply with the standards of the International Electrotechnical Commission (IEC). © 2021 Published under licence by IOP Publishing Ltd.

This work was supported by the Peruvian science foundation CIENCIACTIVA of CONCYTEC and DAAD-CONCYTEC project (2017–2019). The Research Management Office (DGI) of the the Pontificia Universidad Católica del Perú (PUCP) project 492-2017. The research activity was performed in the framework of the doctoral scholarship of L. F. Flores under the contract number 236-2015-FONDECYT. The authors are also thankful to the Center of Materials Characterization (CAM) and the Institute of Corrosion and Protection (ICP) of the PUCP for the EDX, PL and FTIR measurements.

The characterization of the nominal power under real operating conditions is crucial for the correct evaluation of a photovoltaic generator. Several earlier studies proposed different methods based on empirical models for the estimation of the nominal power. These methods require experimental data obtained during optimal days under clear sky conditions and are not suitable for days deviating from these optimal conditions and, thus, generating a significant amount of noise in the data. In this sense, we propose a non-parametric statistical approach to filter out this noise to reliably estimate the real nominal power in the latter conditions. The period of study was 107 days. These were divided in two categories, clear and partly cloudy sky conditions. The results show that our statistical method allows to obtain the same nominal power under partly cloudy conditions as under clear sky. Thi...

This work presents the firsts results of the experimental characterization campaign under outdoor conditions carried out with three different photovoltaic (PV) module technologies: Standard poly-crystalline silicon (poly-Si) aluminum back surface field (Al-BSF) cells, mono-crystalline (c-Si) Heterojunction with Intrinsic Thin-Layer (HIT) cells, and amorphous and microcrystalline silicon (a-Si/µc-Si) thin-film tandem cells. We studied the behavior of these PV technologies and their performance in Lima's desertic and coastal climate during the period from May 2019 to July 2019. For this study, a new outdoor-PV laboratory was implemented at the Pontificia Universidad Católica del Perú (PUCP) with the help of the IDEA research group of the University of Jaén (UJA), Spain. The laboratory enables the characterization of PV modules by extracting the electrical parameters from the current-vo...