• Energy Research

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Accurate characterization and reporting of organic photovoltaic (OPV) device performance reniains one of the important challenges in the field. The large spread among the efficiencies of devices with the same structure reported by different groups is significantly caused by different procedures and equipment used during testing. The presented article addresses this issue by offering a new method of device testing using "suitcase sample" approach combined with outdoor testing that limits the diversity of the equipment, and a strict measurement protocol. A round robin outdoor characterization of roll-to-roll coated OPV cells and modules conducted among 46 laboratories worldwide is presented, where the samples and the testing equipment were integrated in a compact suitcase that served both as a sample transportation tool and as a holder and test equipment during testing. In addition, an internet based coordination was used via plasticphotovoltaics.org that allowed fast and efficient communication among participants and provided a controlled reporting format for the results that eased the analysis of the data. The reported deviations among the laboratories were limited to 5% when compared to the Si reference device integrated in the suitcase and were up to 8% when calculated using the local irradiance data. Therefore, this method offers a fast, cheap and efficient tool for sample sharing and testing that allows conducting outdoor measurements of OPV devices in a reproducible manner. (C) 2014 Elsevier B.V. All rights reserved.

Abstract The emerging thin-film photovoltaic (PV) technologies show the potential to compete in the future market with the currently dominant crystalline silicon (c-Si) technology. A comparison of the different technologies based on their module performance rated at Standard Test Conditions (STC) is a commonly accepted method in the PV community. However, despite being a useful tool, it does not give enough information to accurately predict how much energy a PV module would deliver in the field when subjected to the wide range of real operating conditions. In this paper we explore a potential screening method for new PV technologies; an energy-based metric to estimate the energy performance (Module Performance Ratio) of a PV module in a certain climate. This is constructed on the basis of validated models, and rigorous power rating measurements performed in controlled laboratory conditions at different temperature and irradiance levels. This method has the advantage that it can be applied to laboratory prototypes of technologies still in development as it does not require that the final product has reached maturity. The method has been applied to three thin-film PV technologies including the very innovative organic photovoltaics (OPV), and a comparison with c-Si is presented. The results obtained from the module performance ratio estimation in five different locations show how the emerging OPV technology performs similarly to some of the most common technologies considered and even outperforms slightly some technologies in some of the studied locations. These results could reinforce and support further development of this technology and its potential applications.

AbstractDye‐sensitized solar cells (DSSCs) are generally known to possess a slow response time for photocurrent generation by incident light. Electrical power measurements can only be accurately made if sufficient time is allowed to complete photocurrent generation, in contrast to the case of c‐Si solar cells. There are two methods which can satisfactorily measure the spectral responsivity (SR) of DSSCs, i.e. the “AC method” and “DC method”. Of these two, the AC method in the IEC 60904‐8 standard is the normal procedure for SR measurement of solar cells. A new setup implemented at ESTI for the SR measurement of DSSCs is presented, making use of a low frequency (≤1 Hz) chopped monochromatic beam produced from a continuous broadband light source with band‐pass filters and lock‐in technique for measurements of the signals. The beam is projected onto the device under test (DUT) and superimposed over continuous white bias light. The procedure for the determination of the absolute SR is presented, and the influence of the slow response for photocurrent generation typical of DSSC devices is investigated. The results obtained with the new setup for standard c‐Si solar cells and DSSCs are reported and discussed, providing a validation of the system. © 2014 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons, Ltd.

ABSTRACTThis paper describes the measurement of photovoltaic module performance over a range of temperatures and irradiances according to the international standard IEC 61853 Part 1. The purpose of this work is to assess the reproducibility of power matrix measurements obtained using two methods specified in the standard: under natural sunlight with a tracker, and with a solar simulator. A comparison of results using the third principal method (under natural sunlight without tracker) is also summarised for completeness. The same measurement techniques have been employed to measure four modules of different technologies, namely mono and poly crystalline Si, CdTe and CIS. The method used to vary the irradiance in the natural sunlight with tracker and solar simulator approaches is based on un‐calibrated mesh filters. The uniformity and effect on spectrum of the mesh filters have been studied, and the impact of these on the measurements estimated. Measurements from all methods are compared over as much of the ranges as possible. The results show that for all modules, the reproducibility is within the estimated measurement uncertainty. The suitability of the different methods is discussed in light of the results and the limitations of the various methods as applied to different modules technologies. On the basis of the results, parts of IEC 61853 Part 1 will be introduced into the ISO 17025 laboratory accreditation at the European Solar Test Installation (ESTI). Copyright © 2013 John Wiley & Sons, Ltd.

Abstract The knowledge of electrical current-voltage (I-V) characteristics of photovoltaic (PV) devices under various irradiance, temperature, and spectral conditions is essential for evaluating the output power and energy production of the devices under various climate conditions. The methods to measure the temperature and irradiance dependences of PV devices power are described in the standards IEC 60891 and IEC 61853-1. Newer PV technologies like organic (OPV) and dye-sensitized (DSSC) devices are rapidly evolving and considerable research effort has addressed alternative approaches to increase efficiency with promising values achieved in the last years. Measurements of the irradiance (G) and temperature (T) dependence of these emerging PV technologies are less established –when available– than those of Si-based devices. In this paper we present a first attempt of power-rating measurement for an OPV mini-module. The measurements were performed with a large-area steady-state solar simulator on a reduced (T,G) range compared to what the standard IEC 61853-1 requires. Nevertheless, they were sufficient to calculate the relative temperature coefficients alpha and beta, which have been satisfactorily compared to previous published values. Also, they provided a first data set for the irradiance dependence of OPV device performance. Finally, the power matrix built from these measurements represents at our knowledge the first data set available for energy rating of OPV technology, as the matrix was done for a single device and for both irradiance and temperature dependencies together.

AbstractDye-sensitized Solar Cells are generally known to possess a slow response to changes in photocurrent generation by incident light. Electrical power measurements of photovoltaic (PV) devices can only be accurately made if sufficient time is allowed for complete photocurrent generation. The generation time increases from typically a few milliseconds in the case of c-Si devices, over tens to hundreds of milliseconds for technologies like back-contact and hetero-junction solar cells, to even longer times for dye-sensitized and some types of perovskite solar cells. In this work we propose a procedure for calibration of slow responding PV devices based on an accurate evaluation of their response time. Starting from a quantitative analysis of the photocurrent signal versus chopping frequency on the spectral responsivity set-up, the measurement of a dye-sensitized solar cell was performed at 1Hz chopping frequency. Then current-voltage (I-V) measurements were performed at different sweep-times and directions, in order to determine the correct parameters for I-V characterization. Combining appropriate spectral responsivity (for determination and correction of spectral mismatch) and I-V measurements yielded a reliable calibration of the device including measurement uncertainty estimation. Based on this work criteria for a reliable calibration of slow responding PV devices are formulated, fulfilling all requirements specified in the standards (IEC 60904 series and IEC 60891).