Extreme sensitivity of dye solar cells to UV‐induced degradation

Aapo Poskela,Kati Miettunen,Peter D Lund,Armi Tiihonen

doi:10.1002/ese3.810

Aapo Poskela, Kati Miettunen + Show 2 more

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https://doi.org/10.1002/ese3.810

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Abstract

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.

Highlights

Nanostructured third-generation solar cells have long attracted interest in the research community
dye solar cells (DSC) 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
The DSCs exposed to UV-filtered full spectrum had degraded to 80% of the initial efficiency by 800 hours and completely by 1300 hours

Summary

Introduction

Nanostructured third-generation solar cells have long attracted interest in the research community. A better understanding of the causes and methods for reducing the rate of degradation is crucial. For dye solar cells (DSC),[2] the lowered performance is commonly caused by the degradation of charge carriers in their electrolyte.[3] This process is called bleaching due to the changes it causes in the electrolyte color, turning conventional iodine-based electrolyte from yellow to transparent, and it has been shown to be greatly accelerated by exposure to UV illumination.[3,4,5] DSCs require UV protection to improve stability,[5] which is often accomplished with a UV cutoff filter, that is, a film that is placed between the light source and the photoactive area of the DSC.[6,7,8]

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