0000000000140236
AUTHOR
Rune Strandberg
showing 28 related works from this author
Comparison of the sensitivity to spectral variation of voltage- and current-matched tandem devices with luminescent coupling and thickness optimizati…
2016
Using models that do not take luminescent coupling into account, voltage-matched tandem devices have previously been shown to be less sensitive to spectral variation than their current-matched counterparts. The present paper compares the spectral sensitivity of voltage-matched and current-matched tandem devices by applying a detailed balance model that takes luminescent coupling into account. Current-matched stacks where the thickness of the top cell thickness has been optimized are also considered. The main finding is that luminescent coupling reduces the difference in spectral sensitivity between voltage-matched and current-matched devices. There is still a significant difference, however…
Improved Temperature Coefficient Modeling through the Recombination Parameter $\gamma$
2020
This study presents an injection dependent numerical model relating Shocldey-Read-Hall defect parameters in crystalline silicon with the recombination parameter $\gamma$ . We demonstrate how the model can be used to predict $\gamma$ for various single level defects. Additionally, we show that $\gamma$ can be significantly influenced by the injection level, in contrast to what is commonly assumed. The injection dependence is found to correlate with the temperature sensitivity of the Shocldey-Read-Hall lifetime. Finally, we demonstrate that the model can be used to predict the temperature coefficient of the open circuit voltage without the use of a temperature dependent measurement, enabling …
An Analytic Approach to the Modeling of Multijunction Solar Cells
2020
Analytic expressions for the $JV$ -characteristics of three types of multijunction configurations are derived. From these, expressions for the short-circuit current, open-circuit voltage, and voltage at the maximum power point are found for multiterminal devices, and for series-connected tandem stacks. For voltage-matched devices, expressions for the optimal ratio of the number of bottom cells to the number of top cells are established. Luminescent coupling is incorporated throughout the article. It should be highlighted that the maximum power point of a series-connected tandem stack is described, with good accuracy for all interesting band gap combinations, by a single analytic expression.…
A summary of expressions for central performance parameters of high efficiency solar cell concepts
2019
This work reviews expressions for central performance parameters of various types of PV-concepts when operating at the radiative limit. Some new expressions not published elsewhere are also included. The performance parameters include the short circuit current density, the open circuit voltage, the maximum power density and the optimal voltage. The cell concepts include single junction cells, cells optically coupled to up- and down-converters, intermediate band solar cells and a couple of implementations of multijunction devices. The Lambert W function is used to express the maximum power density.
The ${JV}$ -Characteristic of Intermediate Band Solar Cells With Overlapping Absorption Coefficients
2017
An analytic expression for the $\textit {JV}$ -characteristic of intermediate band (IB) solar cells with overlapping absorption coefficients is derived. The characteristic contains six voltage-independent parameters that are calculated from material properties, cell properties, and external conditions. Combined with exponential functions containing the cell voltage, these describe the full $\textit {JV}$ -characteristic. Expressions are also derived for the short-circuit current and open-circuit voltage. The model represents a major simplification compared with the existing model for this type of devices. The simplicity will facilitate the understanding of the operation of such cells. Furth…
Reduction of temperature coefficients in multicrystalline silicon solar cells after light-induced degradation
2015
This study focuses on the variations of the temperature coefficients after light-induced degradation (LID) of compensated multicrystalline silicon solar cells from three different ingots. The ingots have been chosen to see the effect of the compensation level, the resistivity and the impact of adding gallium to keep the resistivity as constant as possible along the ingot. The temperature coefficients of the efficiency experience a major decrease after LID on all ingots. We found that this decrease varies along the ingot height and does not correspond to the VOC drop. Moreover, no direct correlation with the interstitial oxygen concentration profiles could be seen.
Spectral and temperature sensitivity of area de-coupled tandem modules
2015
- Area de-coupling is a recently suggested method for current- or voltage-matching two-terminal tandem modules. It has previously been shown that under standard conditions, area de-coupled modules have the same theoretical efficiency as four-terminal tandem cells for any combinations of band gaps. In this work, the spectral and temperature sensitivity of ideal area de-coupled modules is investigated by detailed balance modeling. Voltage-matched area de-coupled modules are found to be considerably less sensitive to changes in the spectrum than current-matched modules. Current-matched modules are, on the other hand, found to be less sensitive to changes in the temperature. Under normal condit…
A high-accuracy calibration method for temperature dependent photoluminescence imaging
2019
This work demonstrates a novel technique for calibrating temperature dependent photoluminescence (PL) images of silicon wafers with high accuracy. The PL signal is calibrated using a heat-controlled photoconductance (PC) stage integrated into the PL imaging system. The PC signal is measured in true steady state condition and used to determine the calibration constant under the same temperature and illumination as the PL image, thus providing a high-precision calibration. This results in a robust method for imaging of important physical parameters, such as the minority carrier lifetime and the implied voltage at different temperatures, as well as the temperature coefficients and the recombin…
Analytical Modeling of the Maximum Power Point with Series Resistance
2021
This paper presents new analytical expressions for the maximum power point voltage, current, and power that have an explicit dependence on the series resistance. An explicit expression that relates the series resistance to well-known solar cell parameters was also derived. The range of the validity of the model, as well as the mathematical assumptions taken to derive it are explained and discussed. To test the accuracy of the derived model, a numerical single-diode model with solar cell parameters whose values can be found in the latest installment of the solar cell efficiency tables was used. The accuracy of the derived model was found to increase with increasing bandgap and to decrease wi…
Temperature Coefficients of Compensated Silicon Solar Cells – Influence of Ingot Position and Blend-in-ratio
2015
Published version of an article in the journal: Energy Procedia. Also available on Science Direct: http://dx.doi.org/10.1016/j.egypro.2015.07.004 Solar-grade silicon made from a metallurgical route presents boron and phosphorus compensation. Earlier work has shown that cells made from such material produce more energy than reference polysilicon modules when the temperature and irradiance is high. In the present study, solar cells from two different ingots with different blend-in-ratios were made from wafers at varying ingot heights in order to investigate how the temperature coefficients vary with compensation level and ingot height. The results suggest that solar modules made with solar ce…
THE LIMITING EFFICIENCY OF FOUR-BAND CELLS REVISITED
2014
The limiting theoretical efficiency of four-band solar cells is revisited. In previous work, researchers have looked at the theoretical efficiency of four band cells where the smallest of the three sub-band gaps is closest to the valence band and the largest closest to the conduction band. In this work, limits are calculated also for other possible band configurations. In multi-band cells, photon selectivity can be assured by adjusting the band widths. The present work shows that previous authors have put too rigid constraints on the band structure to achieve spectral selectivity. Relieving these constraints gives a considerably higher limiting efficiency for cells with band width restricti…
On the Variability of the Temperature Coefficients of mc-Si Solar Cells with Irradiance
2016
Abstract The temperature sensitivity of silicon solar cells is in general assumed to be constant with irradiance in PV forecasting models, although it has been demonstrated experimentally that this is not true. In this study a theoretical model is established that describes the variation of the temperature coefficients of a silicon solar cell as a function of the irradiance. It is shown that the temperature sensitivity of the solar cell efficiency is decreasing with the irradiance and that the main reason for this behavior comes from the increase of the open-circuit voltage with light intensity. Moreover, a dependency of the cell's ideality factor on the irradiance has to be assumed to rece…
Analytical Expressions for Radiative Losses in Solar Cells
2019
Analytical expressions for the fundamental losses in single junction solar cells are revised and improved. The losses are, as far as possible, described using parameters with clear physical interpretations. One important improvement compared to earlier work is the use of Lambert’s W function, which allows for analytical expressions for the voltage and current at the maximum power point. Other improvements include the use of Stefan Boltzmann’s law to describe the incoming energy flux as well as taking into account the fermionic nature of the electrons when calculating the thermalization loss. A new expression, which combines emission, Boltzmann and Carnot losses, is presented. Finally, an ex…
Temperature Dependent Suns-V<inf>oc</inf> of Multicrystalline Silicon Solar Cells from Different Ingot Positions
2018
This paper presents temperature dependent Suns- Voc measurements on multicrystalline silicon cells originating from different ingot positions. The effective lifetime is found to increase for all cells when the temperature is increased from 25°C to 6°C. However, cells from the top of the ingot show a considerably larger increas 40–50% for illumination conditions of 0.1-1 Sun, compared to an increase of 20-30% observed for cells from the bottom. The decrease in Voc with increasing temperature is found to be lower for cells from the top of the ingot compared to cells from the bottom. The temperature coefficient of the Voc is found to vary 5% along the ingot at 1 Sun, highlighting the influence…
Assessment of a New Analytical Expression for the Maximum-Power Point Voltage with Series Resistance
2021
This work compares a recently developed analytical expression for the maximum-power point voltage with experimental data, to test its usability for crystalline silicon solar cells. The experimental data covers measurements from 18 multicrystalline silicon solar cells with different bulk resistivities and cell architectures. We show that the expression is able to predict the maximum power obtainable by the measured cells with relative discrepancies below 1%. Additionally, we compare the accuracy of this new expression with two already existing models.
Detailed balance analysis of area de-coupled double tandem photovoltaic modules
2015
Published version of an article in the journal: Applied Physics Letters. Also available from the publisher at: http://dx.doi.org/10.1063/1.4906602 This paper describes how layers of area de-coupled top and bottom cells in photovoltaic tandem modules can increase the efficiency of two-terminal tandem devices. The point of the area de-coupling is to allow the number of top cells to differ from the number of bottom cells. Within each of the layers, the cells can be horizontally series-connected and the layers can then be currentor voltage-matched with each other in a tandem module. Using detailed balance modeling, it is shown that two-terminal tandem modules of this type can achieve the same t…
Theoretical efficiency limits for thermoradiative energy conversion
2015
Published version of an article in the journal: Journal of Applied Physics. Also available from the publisher at: http://dx.doi.org/10.1063/1.4907392 A new method to produce electricity from heat called thermoradiative energy conversion is analyzed. The method is based on sustaining a difference in the chemical potential for electron populations above and below an energy gap and let this difference drive a current through an electric circuit. The difference in chemical potential originates from an imbalance in the excitation and de-excitation of electrons across the energy gap. The method has similarities to thermophotovoltaics and conventional photovoltaics. While photovoltaic cells absorb…
How Gettering Affects the Temperature Sensitivity of the Implied Open Circuit Voltage of Multicrystalline Silicon Wafers
2019
The temperature sensitivity of the open circuit voltage of a solar cell is mainly driven by changes in the intrinsic carrier concentration, but also by the temperature dependence of the limiting recombination mechanisms in the cell. This paper investigates the influence of recombination through metallic impurities on the temperature sensitivity of multicrystalline silicon wafers. Spatially resolved temperature dependent analysis is performed to evaluate the temperature sensitivity of wafers from different brick positions before and after being subjected to phosphorus diffusion gettering. Local spatial analysis is performed on intra-grain areas, dislocation clusters and grain boundaries. Lar…
Temperature Coefficients of Crystal Defects in Multicrystalline Silicon Wafers
2020
This article investigates the influence of crystallographic defects on the temperature sensitivity of multicrystalline silicon wafers. The thermal characteristics of the implied open-circuit voltage is assessed since it determines most of the total temperature sensitivity of the material. Spatially resolved temperature-dependent analysis is performed on wafers from various brick positions; intragrain regions, grain boundaries, and dislocation clusters are examined. The crystal regions are studied before and after subjecting the wafers to phosphorus gettering, aiming to alter the metallic impurity concentration in various regions across the wafers. Most intragrain regions and grain boundarie…
Analytic $JV$ -Characteristics of Ideal Intermediate Band Solar Cells and Solar Cells With Up and Downconverters
2017
The ideal diode equation is regularly used to describe the $\textit {JV}$ -characteristic of single junction solar cells. The connection between the diode equation and fundamental physics is the application of the Boltzmann approximation to describe the fluxes of photons emitted by the cell. In this paper, this approximation is used to derive analytic $\textit {JV}$ -characteristics for three photovoltaic high-efficiency concepts, intermediate band solar cells, and solar cells optically coupled to up and downconverters. These three concepts share the common feature that they allow excitation of electrons between at least three energy levels, which assures a better utilization of the solar s…
Temperature Coefficients of Solar Cell Parameters at Maximum Power Point
2020
Analytical expressions for the temperature coefficients of the maximum power point voltage and current are presented. The temperature coefficients are calculated assuming the bandgap to be a linear function of the temperature and accounting for energy losses of non-radiative nature. The latter are introduced in the model through the External Radiative Efficiency. The so-called $\gamma$ parameter, which has been shown to account for the thermal sensitivity of all mechanisms determining the open-circuit voltage, appears to also play a role in the temperature coefficient of the maximum power point voltage and current. Numerical results and a comparison with experimental measurements are also p…
Temperature Sensitivity of Multicrystalline Silicon Solar Cells
2019
This paper presents an experimental investigation of the temperature coefficients of multicrystalline silicon solar cells. The aim was to determine if some cell parameters can affect positively the temperature sensitivity without detrimental impact on the efficiency. Commercial solar cells with different bulk resistivities, compensation levels, and cell architectures have been studied. We report that the base net doping, the location of the solar cell along the brick and the cell architecture have significant impacts on the temperature coefficients. Moreover, we show how the change in recombination mechanisms along the ingot height affects the temperature coefficients. The compensation leve…
Minority Carrier Lifetime Variations in Multicrystalline Silicon Wafers with Temperature and Ingot Position
2017
The minority carrier lifetimes of multicrystalline silicon wafers are mapped using microwave photoconductive decay for different temperatures and ingot positions. Wafers from the top of the ingot display larger areas with lower lifetimes compared to wafers from the bottom. The lifetimes of low-lifetime areas are found to increase with the temperature, while the lifetimes of some high-lifetime areas decrease or remain unchanged. The relative improvement of the low-lifetime areas is considerably larger than the relative change in the high-lifetime areas. We suggest that the above-mentioned observations explain, at least partially, why previous studies have found the relative temperature coeff…
Analytic JV-Characteristics of Ideal Impurity PV-Cells
2017
In this article the mathematical modeling of idealized impurity photovoltaic cells is greatly simplified through the derivation of analytic JV-characteristics. The resulting expressions are also facilitating the intuitive understanding of such photovoltaic devices. The new model is used to investigate the sensitivity of impurity photovoltaic cells to the absorption band width, the impurity related absorptivity and the external radiative efficiency. It is found that impurities with narrow absorption bands or low absorptivity can greatly reduce the efficiency of the device, even if they are fully radiative and have energy levels situated at optimal positions in the band gap. It is also found …
Heat to electricity conversion by cold carrier emissive energy harvesters
2015
This paper suggests a method to convert heat to electricity by the use of devices called cold carrier emissive energy harvesters (cold carrier EEHs). The working principle of such converters is explained and theoretical power densities and efficiencies are calculated for ideal devices. Cold carrier EEHs are based on the same device structure as hot carrier solar cells, but works in an opposite way. Whereas a hot carrier solar cell receives net radiation from the sun and converts some of this radiative heat flow into electricity, a cold carrier EEH sustains a net outflux of radiation to the surroundings while converting some of the energy supplied to it into electricity. It is shown that the…
Analytical Modeling of the Temperature Sensitivity of the Maximum Power Point of Solar Cells
2022
Author's accepted manuscript Abstract—This article presents new analytical expressions for the temperature coefficients of the voltage, current, and power of a solar cell at its maximum power point MPP). A new analytical expression of the temperature coefficient of the fill factor is also derived. The new expressions are written as functions of photovoltaic (PV) metrics that can be obtained from i-V measurements. Nonideal diode behavior is partially accounted for through a temperature dependent ideality factor. The recombination parameter γ, which has been shown to account for the thermal sensitivity of all mechanisms determining the open-circuit voltage, appears to play a role also for the…
Reduced temperature sensitivity of multicrystalline silicon solar cells with low ingot resistivity
2016
This study presents experimental data on the reduction of temperature sensitivity of multicrystalline silicon solar cells made from low resistivity ingot. The temperature coefficients of solar cells produced from different ingot resistivities are compared, and the advantages of increasing the net doping are explained.
Using transfer coefficients to model series-connected multi-junction solarcells with radiative coupling
2023
Author's accepted manuscript This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Strandberg, R. (2023). Using transfer coefficients to model series-connected multi-junction solar cells with radiative coupling. Applied Physics Letters, 122(25), 1-6 and may be found at https://doi.org/10.1063/5.0152026. When the quality of multi-junction solar cells becomes sufficiently high, radiative exchange of photons between cells must be included to properly model such devices. In this work, it is shown how constants called transfer coefficients can account for radiative coupling in series-connected mult…