• Energy Research

Urgent deficiencies in the aging tests of perovskite and dye solar cells are identified and improved methods are proposed in this work.

Abstract A simple and non-destructive method is introduced using image processing to investigate changes in the performance of the dye solar cells (DSCs). The main principle is based on the fact that the most important DSC components (dye, electrolyte, catalyst) have a specific color which often changes as result of degradation. Here the imaging technique is demonstrated in the case of exposing DSCs on very harsh conditions (85 °C temperature and UV + Visible light). The aging of the cells was recorded with a color sensitive camera in a well regulated setup and the photographs were processed using image analysis techniques. A key factor in making the imaging method quantitative and suitable for aging studies is color calibration which is explained in detail. The image analysis of different cell configurations revealed that the bleaching reactions of the electrolyte were related to reactions between TiO 2 and the electrolyte. The dye layer on the TiO 2 was shown slow down the degradation. Furthermore the comparison of image analysis and current–voltage curves indicated that the performance degradation of the cells was only partly due to loss of tri-iodide. The loss of photocurrent and photovoltage was apparently largely due to the harmful effect of the by-products of the bleaching and/or the degradation of the dye. In addition, a small recovery effect due to the generation of tri-iodide under reverse bias condition was seen in both image analysis and electrical measurements.

Please cite the original version: Miettunen, Kati & Saukkonen, Tapio & Li, Xiaoe & Law, ChunHung & Sheng, Yeo Kee & Halme, Janne & Tiihonen, Armi & Barnes, Piers R. F. & Ghaddar, Tarek & Asghar, Imran & Lund, Peter & O'Regan, Brian C.. 2012. Do Counter Electrodes on Metal Substrates Work with Cobalt Complex Based Electrolyte in Dye Sensitized Solar Cells?. Journal of the Electrochemical Society. Volume 160, Issue 2. H132-H137. ISSN 0013-4651 (printed). DOI: 10.1149/2.074302jes.

In this study the effect of the purification of electrolyte material on the performance and long-term stability of dye-sensitized solar cells is investigated. The combined effect of purifying all the electrolyte materials has been examined, as has the effect of purifying each compound to identify those compounds worth purifying and to eliminate unnecessary production steps on an industrial scale. Statistical methods were employed to draw statistically significant conclusions from the experimental results. No effect on the initial cell performance is found in this study. The purity of the electrolyte solvent (here methoxypropionitrile) is shown to have a remarkable effect on the cell lifetime: it could even double when the cell is properly purified. It is shown that exposing the cell to even relatively small amounts of UV light resulted in cell degradation through electrolyte bleaching during a 1000 hour aging test. Here the impurities in the electrolyte solvent lead to an almost doubled rate of electrolyte bleaching under UV light. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any

The current status of the long-term stability of dye solar cells (DSCs) and factors affecting it is reviewed. The purpose is to clarify present knowledge of degradation phenomena and factors in these cells by critically separating the assumptions from the solid experimental evidence reported in the literature. Important degradation processes such as dye desorption, decrease in the tri-iodide concentration, degradation at the photoelectrode and counter electrode, affect of ultraviolet light and moisture, and issues related to the sealing, are covered. It is concluded that techniques giving chemical information are needed for the stability investigations of DSCs to reveal possible ways to improve their lifetime. In this regard, experimental methods suitable for separating degradation mechanisms in complete cells during long-term testing are proposed employing specifically designed sealed cell structures, called segmented cells, that provide windows to measure specific cell components without being obscured by the others.

AbstractPresent practice to avoid harmful effects of UV light on dye solar cells (DSC) is to use a UV filter. However, we show here that a standard 400 nm UV cutoff filter offers inadequate protection from UV‐induced degradation. DSCs that were exposed to only visible light by LED lamps maintained 100% of their initial efficiency after 3000 hours of exposure, whereas the efficiency of DSCs subjected to full light spectrum (Xenon arc lamp) with an efficient UV filter dropped down to 10% of their initial performance already after 1500 hours. Optical analysis of the UV filter confirmed that the amount of light transmitted below 400 nm was negligible. These observations indicate that (a) DSCs can be very sensitive to even minor amount of UV and (b) eliminating the effects of UV light on DSC stability cannot easily be avoided by a UV filter on top of the cell. A detailed analysis of the degradation mechanisms revealed that the culprit to loss of performance was accelerated loss of charge carriers in the electrolyte of the DSCs—a typical symptom of UV exposure. These results suggest that commonly used stability tests under LED illumination are insufficient in predicting the lifetime of DSCs in outdoor conditions. Instead, for such purpose, we recommend solar cell stability to be tested with a full light spectrum and with a suitable UV filter.

Stainless steel based dye solar cells have been upscaled from small, laboratory size test cells of 0.32 cm2 active area to 6 cm x 6 cm "mini-modules" with active areas ca. 15 cm2. Stainless steel works as the photoelectrode substrate whilst the counter electrode is prepared on indium-doped tin oxide coated polyethyleneterephtalate or polyethylenenaphtalate plastic foil (fluorine-doped tin oxide coated glass as a reference). Additional current collector structures were deposited on the counter electrode substrate with inkjet-printing of silver nanoparticle ink in order to reduce the lateral resistance of the plastic foil. Flexible substrates enable roll-to-roll type industrial manufacturing of the cells and the steel's superior conductivity compared to the typical substrate materials such as glass and plastic makes it possible to prepare even substantially larger modules. The best efficiencies obtained this far with the "mini-module" using a stainless steel photoelectrode are 2.5% with a platinum-sputtered indium-doped tin oxide coated polyethyleneterephtalate counter electrode and 3.4% with a thermally platinized fluorine-doped tin oxide coated glass counter electrode. These efficiencies are on the same level than those measured with small cells prepared with similar methods and materials (3.4%-4.7%, depending on configuration, which are amongst the highest reported for this kind of a dye solar cell). Replacing expensive conducting glass with steel and plastic foils as the substrate materials leads also to economical savings in the cell production.

AbstractPlant‐based materials are emerging as an alternative to conventional components in advanced energy applications. Among these, energy harvesting from sunlight is highly attractive and, in fact, represents the fastest growing energy technology. This review addresses the broad field of solar cell science since plant‐based components can be utilized in almost all solar technologies, and in certain photovoltaic technologies, they can fulfill most of the roles in photovoltaic devices. There is strengthened recent interest in developing sustainable materials options as well as new functionalities being developed for bio‐based materials. This contribution describes the different options for plant‐derived materials in photovoltaics and discusses their deployment feasibility. We focus on performance, lifetime, and embedded energy, all of which are critical to achieve—economically and sustainably–competitive photovoltaic devices. We address the tendency in the current literature for greenwashing, given that not all plant‐based solutions are environmentally‐sound at the device level. On the other hand, plant‐based materials can offer functionalities that cannot be reached with currently used materials.This article is categorized under: Sustainable Energy > Solar Energy Emerging Technologies > Materials Sustainable Energy > Bioenergy