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Fabrication and luminescence properties in Yb–Tb co-doped a-SiCO thin films
(VBRI Press, 2020-07-24)
Amorphous silicon oxycarbide (a-SiCxOy) single doped with Yb3+ and co-doped with the couple Tb3+ - Yb3+ thin films were grown on crystalline silicon substrates by rf magnetron sputtering. The elemental composition in at. % is determined by energy dispersive spectroscopy and fourier transform infrared spectroscopy allows to investigate the chemical properties of the host. The concentration of Yb in the single doped sample was 3.5% and for the codoped samples (Yb, Tb) were (3%, 0.9%), (3.5%, 0.6%) and (4%, 0.6%), respectively. Post-deposition annealing treatments were made in order to induce optical activation of the rare earths. Conversion or absorption of high energy photons were analyzed by photoluminescence spectroscopy. The photoluminescence spectra show that for a given temperature range in the thermal annealing process, as well as for the appropriate rare earth concentrations the activation of Yb3+ and Tb3+ is enhanced. A strong reduction of the Tb3+ emission in contrast to the Yb3+ emission in the a-SiCxOy,:Tb:Yb samples at annealing temperature at 500°C suggests a energy transfer from Tb3+ to Yb3+ ions. Copyright © 2018 VBRI Press.
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Impact of measured spectrum variation on solar photovoltaic efficiencies worldwide
(Center for Open Science, 2021-09-02)
In ratings of solar photovoltaic performance, variation in the spectrum of sunlight is commonly neglected. A single spectrum, AM1.5, is used as the sole basis not only for record laboratory efficiencies, but also for commercial module power ratings, the performance metrics for solar power plants, and warranty claims. Incorporation of solar spectrum variation would improve accuracy and reduce the financial consequences of prediction errors. Ground-level measurements of spectral irradiance collected worldwide have been pooled to provide an extensive – though by no means comprehensive – sampling of the variation. Applied to nine solar cell types, the resulting divergence in solar cell performance illustrates that a single spectrum is insufficient for comparison of cells with different spectral responses. In contrast with single-junction cells such as silicon and cadmium telluride, cells with two or more semiconductor junctions tend to have efficiencies below that obtained under AM1.5. Increases in the degree of sun tracking are shown to decrease efficiency for cells with a narrower spectral response. Of the nine cell types, silicon exhibits the least spectral sensitivity: relative site variation ranges from 1% in Lima, Peru to 14% in Edmonton, Canada, with a mean of 4%.
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Identifying barriers and opportunities in the deployment of the residential photovoltaic prosumer segment in Chile
(Elsevier, 2021-06-01)
Photovoltaic (PV) prosumers can play a significant role in the transition toward sustainable cities. However, the implementation of more effective policies which accelerate the deployment of this market is needed. In this study, after an overview of the residential PV prosumer (RPVP) market's status in Chile, critical parameters that can speed-up the deployment of this segment through policy decisions were identified. Considering the local conditions of each regional capital in Chile, the segment is analyzed with widely-used econometric techniques to evaluate the residential PV systems feasibility empirically. The results show that the Chilean regulatory framework is insufficient for exploiting the potential of the RPVP. Without effective policy instruments, high investment costs and low income per household are the main barriers in the deployment of the segment in this country. Therefore, suitable promotion energy policies, regulatory changes, and financing options can accelerate the deployment without majorly impacting on the national budget. This would let citizens help accelerate decarbonization through a more decentralized and democratic energy transition, gaining socio-economic and socio-environmental benefits, based on solar PV technology.
2
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Estimation of the effective nominal power of a photovoltaic generator under non-ideal operating conditions
(Elsevier, 2021-12-20)
The nominal power is an essential parameter for evaluating the general state of a photovoltaic plant. The American Society for Testing and Materials, the International Electrotechnical Commission and other works propose procedures that allow estimating the nominal power of a photovoltaic generator in outdoor conditions. These procedures generally require monitoring days with ideal conditions, particularly clear sky days with high irradiance values and low wind speeds. These restrictions can limit the available number of monitoring days, especially in places with frequent cloud formations. In this work, a 109.44 kW photovoltaic plant was monitored for six months in Granada, Spain. Its nominal power is first estimated applying a referential procedure reported in the literature for large PV plants under the required ideal climatic conditions. In order to overcome the restrictions for estimating the nominal power, we propose a new procedure applicable not only for ideal but also for non-ideal conditions, such as found on partially cloudy days. This new procedure applies non-parametric statistics to find the most probable value of the nominal power within a single monitoring day. A statistical analysis indicates that it reliably estimates the nominal power at non-ideal conditions while preserving the same estimation accuracy as under ideal conditions.
3
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Spectral effects on the energy yield of various photovoltaic technologies in Lima (Peru)
(Elsevier, 2021-05-15)
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 monthly APE value variations. This nearly negligible seasonality could be attributed to the low latitude and the particular climate in Lima. Larger-bandgap PV technologies, such as a-Si, perovskite, and CdTe, resulted in annual spectral gains of +6.8%, +4.8%, and +2.1%, respectively. Lower-bandgap PV technologies (CIGS-2, multi-Si, CIGS-1, and mono-Si), present small annual spectral gains of −0.9%, −1.4%, −1.6% and −2.3%, respectively. Also, a quasi-linear correlation between APE and MM was found for all PV technologies.
2
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Impact of measured spectrum variation on solar photovoltaic efficiencies worldwide
(Elsevier Ltd, 2022-08-01)
In photovoltaic power ratings, a single solar spectrum, AM1.5, is the de facto standard for record laboratory efficiencies, commercial module specifications, and performance ratios of solar power plants. More detailed energy analysis that accounts for local spectral irradiance, along with temperature and broadband irradiance, reduces forecast errors to expand the grid utility of solar energy. Here, ground-level measurements of spectral irradiance collected worldwide have been pooled to provide a sampling of geographic, seasonal, and diurnal variation. Applied to nine solar cell types, the resulting divergence in solar cell efficiencies illustrates that a single spectrum is insufficient for comparisons of cells with different spectral responses. Cells with two or more junctions tend to have efficiencies below that under the standard spectrum. Silicon exhibits the least spectral sensitivity: relative weekly site variation ranges from 1% in Lima, Peru to 14% in Edmonton, Canada.
2
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Hydrogen effects at sputtered Tb-doped AlNxOy:H / c-Si(p) interfaces: A transient surface photovoltage spectroscopy study
(Elsevier B.V., 2022-10-01)
In the present work, we studied the interface of terbium doped aluminum oxynitride (Tb-doped AlNxOy:H) deposited under different hydrogen flows with p-type doped crystalline silicon by applying transient surface photovoltage spectroscopy. We observed strong accumulation with concomitant passivation of boron acceptors in the crystalline silicon and defect generation near the interface. With increasing hydrogen flows, the net negative charge in the Tb-doped AlNxOy:H layer decreased, surface photovoltage signals related to defects increased, surface photovoltage transients decayed faster, and the slowest relaxation of charge carriers separated in space changed from trap limited to hopping transport via an exponential distribution of trap states in energy.
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Indirect excitation and luminescence activation of Tb doped indium tin oxide and its impact on the host's optical and electrical properties
(IOP Publishing Ltd, 2022-05-26)
The effect of adding terbium to indium tin oxide (ITO) thin films on the electrical, optical and light emission properties was investigated. The films were prepared by radio frequency dual magnetron sputtering, maintaining a high optical transmittance in the ultraviolet and visible spectral regions, and a low electrical resistivity ranging from 5 × 10 − 3 Ω ⋅ cm to 0.3 Ω ⋅ cm . Terbium-related luminescence is achieved after annealing at 470 ∘C in air at atmospheric pressure. Electrical resistivity and optical transmittance were measured after each annealing step to evaluate the compromise between the achieved light emission intensity, electrical and optical properties. Additionally, temperature dependence of Tb-related luminescence quenching was assessed by temperature-dependent photoluminescence measurements, from 83 to 533 K, under non-resonant excitation. Thermal quenching activation energies suggest an effective energy transfer mechanism from the ITO host to the rare-earth (RE) ions. This indirect excitation mechanism was modeled using a spherical potential-well and a tight-binding one-band approximation approaches, describing a short-range charge trapping process and subsequent formation of bound excitons to RE ion clusters.
2
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Assessing the accuracy of analytical methods for extracting parameters of different PV module technologies under clear and cloudy sky conditions
(Elsevier Ltd, 2024-12-01)
Accurately determining single-diode model parameters yields essential insights into the photovoltaic (PV) device performance and behavior. Analytical methods for extracting these parameters often rely on mathematical assumptions typically valid under controlled indoor conditions. Applying these methods to PV modules in the field introduces complexities due to varying environmental conditions and module technologies, leading to divergencies between parameters extracted under outdoor and indoor conditions. This study closes the gap in analyzing the retrieved parameters under intricate outdoor conditions by differentiating between all-, clear-, and cloudy-sky conditions and varying irradiances for different PV technologies. We examine three methods over a year of outdoor I-V curves from Al-BSF, HIT, and a-Si/µc-Si PV modules in Lima, Peru, a low-latitude site. The findings represent the first mid-term study by the country's premier laboratory uniquely equipped for diverse outdoor PV module characterization. We evaluate the accuracy of each method using the Normalized Root Mean Square Error (NRMSE) by comparing experimental against simulated I-V curves derived from the extracted parameters. Our findings reveal that the parameters for the Al-BSF and HIT modules under all-sky conditions align with reported outdoor trends for varying irradiances, while under clear skies, they correspond with indoor trends. In terms of accuracy, the methods by Phang et al. and de Blas et al. consistently achieve an average NRMSE below 1 % across all PV module types under all-sky conditions. However, when differentiating between sky conditions, the NRMSE values for the Al-BSF and HIT modules are notably lower under clear sky conditions at any irradiance level, preserving a mean value below 0.6 %, unlike the a-Si/µc-Si PV technology, which shows more consistent NRMSE values across all sky conditions and most irradiance levels and in average above 0.7 %. These results demonstrate that selecting sky conditions based on the evaluated PV technology is beneficial for enhanced accuracy in outdoor parameter extraction.
1
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Predictability and Interrelations of Spectral Indicators for PV Performance in Multiple Latitudes and Climates
(Elsevier Ltd, 2023-07-15)
When PV is installed in the field, the module technologies are rated according to their output energy yield under local operating conditions rather than at standard test conditions (STC), where the spectrum is set to AM1.5G. Care must be taken as this standard is not optimal for all latitudes and the solar spectral distribution variations are one primary influencing factor on PV performance. In addition, obtaining an accurate estimate of the spectral effects on PV performance, as set out in standard procedures, is hampered by the cost of gathering the inputs and the large amount of spectral data required for such a calculation. In this work, based on measured spectral irradiance data from nine sites of different latitudes and climates, we first show a characteristic trend in the spectral distribution over the year concerning the location latitude. The closer a site is to the equator, the more blue-rich the solar spectrum is and the fewer seasonal spectral variations it will contain. Then, we calculate and correlate the most popular metrics (device-independent and device-dependent) used to describe the influence of solar spectra on PV performance. In particular, the monthly irradiance-weighted Spectral Mismatch Factor for different PV technologies and Average Photon Energy show a global linear correlation for data from these nine sites. We use this global linear relationship to propose PV technology-dependent equations that predict annual and monthly spectral gains/losses within a prediction half-interval of up to ± 1.66% by only inserting the monthly or annual irradiance-weighted Average Photon Energy potentially for any site. Reducing the required spectral data sets for performance estimation through our methodology facilitates a more accessible and less costly communication of databases than complete spectral data sets. Finally, using this spectral data, we demonstrate statistically that the Spectral Mismatch Factor and Integrated Useful Fraction Ratio can be replaced by alternative spectral metrics, which require only averaged spectra and, thus, reduce the computational effort to estimate the above indicators.
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