Cover Image Bhoopathy, Raghavi; Kunz, Oliver; Juhl, Mattias ...
Progress in photovoltaics,
March 2020, Volume:
28, Issue:
3
Journal Article
Peer reviewed
The cover image is based on the Applications Outdoor photoluminescence imaging of solar panels by contactless switching: Technical considerations and applications by Raghavi Bhoopathy al., ...https://doi.org/10.1002/pip.3216.
The internal quantum efficiency (IQE) is given as the ratio between the externally collected electron current and the photon current absorbed by the device. Spectral analysis of IQE measurements is a ...powerful method to identify performance‐limiting mechanisms in solar cells. It also enables the extraction of key electrical and optical parameters. However, the potential of IQE measurements is only rarely fully utilized, presumably due to the significant complexity associated with the fitting process and its sensitivity to noise. In this study, machine learning is proposed as an efficient method to extract quantitative information from IQE measurements. The extraction method is automated and easy to use, providing an array of specific device parameters. By simplifying the analytical process, the developed machine learning algorithms also extract the parasitic absorption of the antireflection coating, a key parameter that is difficult to obtain by traditional methods. Although the method has been developed for and tested on silicon solar cells, it can be adapted and applied to other types of solar cells.
This study presents a unique approach to analyzing the internal quantum efficiency (IQE) of solar cells. Machine learning chain regressors were trained to extract the key electrical and optical parameters from IQE measurements, achieving extremely low error scores. Upon testing on different cell structures, the trained models achieved better performance than traditional fitting methods. The method can be adapted to a wide range of solar cell materials and technologies.
Performance monitoring of crystalline silicon solar cells often requires terminal voltage measurements, which are strongly influenced by the sample temperature via the large temperature dependence of ...the intrinsic carrier density. The impact of sample temperature variations can be corrected for by using the temperature coefficient of the terminal voltage, however this relies on having both accurate values for the temperature coefficient and accurate measurements of the sample temperature. This paper demonstrates that in situations where the sample temperature cannot be accurately measured, for example in some high volume production facilities or during module degradation experiments, implied voltages determined from either electroluminescence or photoluminescence provide a more accurate measure of sample performance than the terminal voltage. The results presented here show that implied voltages exhibit a temperature sensitivity that is one order of magnitude lower than that of the terminal voltage. This is largely due to the fact that luminescence intensity is not strongly temperature dependent around room temperature. This is confirmed by experimental temperature dependent measurements on four different crystalline silicon solar cell types. The benefit of using implied voltage measurements over temperature corrected terminal voltage measurements for the monitoring of light and elevated temperature induced degradation in silicon solar modules is demonstrated.
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•Terminal voltage measurements are known to have a very strong temperature dependence.•The temperature coefficient of implied voltages from luminescence is one order of magnitude lower in comparison.•Implied voltage measurements are preferred when data regarding sample temperature variations is unavailable or inaccurate.•Temperature correction is not required to accurately monitor module performance using implied voltages from luminescence.•Results are valid for different crystalline silicon solar cell types and for fully assembled modules.
Light emitting diodes (LEDs) are increasingly being used as light sources in studying solar cells due to their high power, low cost, and long bulb lifetimes. However, LEDs do not provide the ...monochromatic illumination that is desired for an external quantum efficiency measurement. This study investigates the error associated with using a broad emission spectrum instead of monochromatic light on measurements of the external quantum efficiency of silicon solar cells. An analytical approach is used to quantify the impact of the finite spectral width of LEDs. The approach is then extended to provide a method that corrects for the resulting error in the measured external quantum efficiency (EQE). It is shown that after applying the correction method to the measured EQE, the absolute error can be reduced from 1%-2% to under 0.5%.
Charge carrier lifetime is an important parameter for semiconductor materials. This study proposes a dynamic calibration method for injection‐dependent carrier lifetime measurements. This method is ...based on the comparison between lifetime measurements under quasi‐steady‐state and non‐quasi‐steady‐state conditions. The proposed method is first demonstrated by numerical simulation. Experimental data are subsequently used to compare the proposed method with conventional calibration methods, demonstrating good agreement between the methods. Furthermore, the calibration method is found to be much less sensitive to measurement noise. When applied to photoluminescence‐based carrier lifetime measurements, the proposed method also provides the net bulk doping concentration.
Measuring the injection‐dependent charge carrier lifetime is an essential characterization technique for semiconductor materials. This paper proposes a dynamic lifetime calibration method. The proposed method is much less sensitive to measurement noise compared to conventional methods. Bulk doping information is also not required and can even be extracted if the proposed method is used for photoluminescence‐based measurements.
Outdoor Photoluminescence imaging of crystalline silicon photovoltaic modules in full daylight via contactless switching of the operating point was recently demonstrated. That previous method ...requires an optical modulator to be placed on at least two positions of each module under test and two or more separate sets of image pairs need to be acquired and combined into a merged PL image.Here we demonstrate a modified approach which enables outdoor PL image acquisition of an entire module from just one image pair. The method still enables image acquisition without any modification of the electrical wiring within the system but is overall simpler and thereby enables significantly higher sample throughput for outdoor PL image acquisition in PV power plants. It also enables imaging of several PV modules at once. The method relies on partial shading of up to five series connected modules and PL image detection of the remaining non-shaded series connected modules within the same module string. In this paper the underlying principles and technical details of this novel method are discussed. Experimental data demonstrating the feasibility of the method are presented, including PL images acquired on state-of-the art bifacial half-cell PV modules.
Abstract
We present a simple yet powerful analysis of Suns‐photoluminescence quantum yield measurements that can be used to determine the surface saturation current densities of thin film ...semiconductors. We apply the method to state‐of‐the‐art polycrystalline perovskite thin films of varying absorber thickness. We show that the non‐radiative bimolecular recombination in these samples originates from the surfaces. To the best of our knowledge, this is the first study to demonstrate and quantify non‐linear (bimolecular) surface recombination in perovskite thin films.
The spatially resolved bulk lifetimes of silicon bricks can be obtained by spectral photoluminescence intensity ratio imaging. The underlying principle of this method, relevant experimental data and ...studies discussing its residual artefacts and limitations were published recently. To further discuss the accuracy and drawbacks of the method, the impact of lateral carrier diffusion into grain boundaries and the influence of free carrier absorption are analysed theoretically. A criterion is given by which the impact of minority carrier diffusion on the bulk lifetime image can be rated depending on both the distance to the grain boundary and the local grain bulk lifetime. We find that the impact of free carrier absorption on the calculation of quantitative bulk lifetime can be neglected for bricks commonly used for solar cell fabrication. However, free carrier absorption needs to be accounted for bricks with lifetimes in the millisecond range such as can be found in Czochralski grown material.
► We perform a 2D electro-optical analysis of grain/grain boundaries structure on thick silicon. ► We give minimal resolvable bulk lifetime feature size as a function of the grain bulk lifetime. ► FCA does not need to be accounted for if PLIR is measured on directional solidified mc-Si bricks. ► FCA does need to be accounted for if PLIR is measured on Cz bricks.
Electroluminescence (EL) imaging is one of the most common characterisation techniques for photovoltaic cells and modules. EL images contain information on both the open-circuit voltage (Voc) and ...series resistance (Rs) of the device. However, separating the two effects and identifying features related to each parameter can be challenging. In this study, a novel approach for decomposing EL images into Voc and Rs maps using a convolutional neural network architecture is presented. A deep learning model was first trained on paired EL and photoluminescence images that were generated using a simulation tool. Results obtained using the validation set show that the trained model is able to accurately differentiate between features related to Voc and Rs in EL images, thus replacing the need for multiple types of measurements. The proposed method presents a unique approach to analyse EL images, unlocking new capabilities that have the potential to advance solar cell characterisation.
