Elsevier

Solar Energy

Volume 85, Issue 6, June 2011, Pages 1179-1188
Solar Energy

Long-term stability of dye solar cells

https://doi.org/10.1016/j.solener.2010.10.016Get rights and content

Abstract

This work provides a review of dye solar cell long-term stability under light and thermal stress factors as well as discussion on the main degradation mechanisms. Performance and EIS parameters of industrial type Z907-based cells were evaluated during the course of continuous light soaking over 25,600 h at 55–60 °C. Only minor degradation occurred under such conditions, with open circuit voltages dropping by 50–80 mV due to a shift of the conduction band towards more positive potentials and with fill factors at high light levels decreasing due to an increase of cell series resistance. There is no evidence of dye degradation, loss of iodine or decrease of Pt electrocatalytic activity. From the accelerated ageing tests, a product life time of 40 years can be extrapolated for Middle European and 25 years for South European conditions. 80 °C storage over 1000 h resulted in 10–20% decrease of performance with ionic liquid or solvent based electrolyte systems, respectively.

Introduction

Dye solar cells (DSC) offer attractive performance at an affordable cost, superior performance under diffuse or otherwise non-ideal light conditions, tunable colouration and/or transparency, flexibility, low weight and low embodied energy. Since the early days of DSC (Desilvestro et al., 1985, O’Regan and Grätzel, 1991), efficiency has continually been improved for laboratory cells to presently 12.2% (Grätzel, 2009), rendering this technology increasingly competitive for practical applications. In order to be successful in the market place, any novel photovoltaic technology has to offer a favourable performance-to-cost ratio and sufficient product durability. For commercially viable building integrated applications, panel life time needs to be 20–25 years. As with any PV technology, a variety of mechanisms can lead to loss of performance over extended periods of time. In the case of DSC, where the principle of operation is based on molecular processes, similar to photosynthesis, some of the mechanisms for loss of performance are fundamentally different from those occurring in other solid-state devices based on p-/n-junctions. This paper will review the main degradation mechanisms in DSC and then present some recent results with industrial type cells.

Section snippets

Review of mechanisms for loss of performance

Degradation can occur at four different levels, i.e. the molecular, cell, module/panel, and system level. Every level is characterised by higher complexity and relies on stability of the lower levels. This study will mainly deal with the molecular and cell aspects.

Materials and preparation of cells

All chemicals used in this work were stored in a dry room (relative humidity ∼2%) and used without any further purification. “Solvent based” electrolyte solutions contained 1-propyl-3-methylimidazolium iodide (PMII, >99%, Merck), iodine (I2, 99.8%, Aldrich) and guanidinium thiocyanate (99.9%, Fluka) in 3-methoxypropionitrile (MPN, 99+%, Fluka). Benzimidazole was used to control titania surface charge in solvent based electrolyte systems to a certain extent. Alternatively, some comparative tests

Light soaking of single cells under resistive load

Materials and dimensions for cells assembled and investigated in this work were all selected in respect to their industrial relevance. Thus only relatively non-volatile and non-toxic electrolyte components were employed and relatively low cost TEC 15 conductive glass was employed. In contrast to many researchers who use ‘spot cells’ of <0.2 cm2 size, where currents and thus resistive losses are small and therefore fill factor and efficiency high, we use dimensions which are representative for

Conclusions

In summary, the results highlighted in this work clearly demonstrate the prospects of DSC technology for extended product with some reservations yet concerning exposure to temperatures above 80 °C continuously. Therefore, applications in moderate climates, e.g. Northern and Middle Europe, but also in situations where the angle of incidence of solar light is not optimum, such as on façades, appear to be ideally suited for DSC market introduction.

Detailed analysis from light soaking data at 55–60 

Acknowledgements

The authors thank Dyesol Limited and numerous members of the team for materials preparation, establishment and maintenance of infrastructure and equipment and for funding this work.

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