Researchers at EPFL in Switzerland have increased the power conversion efficiency of dye-sensitized transparent solar cells beyond 15% in direct sunlight and 30% in ambient light conditions.
Mesoscopic dye-sensitized solar cells (DSCs) were invented in 1990s by Brian O’Regan and Michael Grätzel, EPFL Professor, and have been called Grätzel cells. DSCs convert light into electricity through photosensitive dyes that absorb light and inject electrons into an array of oxide nanocrystals which subsequently are collected as electric current.
In DSCs, photosensitizers are attached to the surface of nanocrystalline mesoporous titanium dioxide films that include redox active electrolytes or a solid charge-transport material.
Researchers from the groups led by Grätzel and Anders Hagfeldt at EPFL have developed a way of improving the packing of two newly designed photosensitizer dye molecules to enhance the photovoltaic performance of the DSC.
Together, the new photosensitizers can harvest light across the entire visible domain. The technique involves pre-adsorbing a monolayer of a derivative of hydroxamic acid on the surface of nanocrystalline mesoporous titanium dioxide. This slows down the adsorption of the two sensitizers, enabling the formation of a well ordered and densely packed layer of sensitizer at the titanium dioxidesurface.
With this approach, the team was able to develop DSCs with a power conversion efficiency of 15.2% for the first time under standard global simulated sunlight, with long-term operational stability tested over 500 hours.
By increasing the active area to 2.8 cm2, the power conversion efficiency spanned 28.4% – 30.2% over a wide range of ambient light intensities along with outstanding stability.
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DSCs are transparent, can be fabricated in multiple colours for low cost, and are already being used in skylights, greenhouses, as well as glass facades, such as those on the SwissTech Convention Centre. Lightweight flexible versions of DSCs are now commercially sold on a large scale for electrical powering of portable electronic devices such as earphones and e-readers, as well in the Internet of Things by using ambient light.
The cosensitization chemical fabrication approach produces DSCs with two or more different dyes that have complementary optical absorption. This has increased the power-conversion efficiencies of DSCs by combining dyes that can absorb light from across the entire light spectrum.
“Our findings pave the way for facile access to high performance DSCs and offer promising prospects for applications as power supply and battery replacement for low-power electronic devices that use ambient light as their energy source,” said the researchers.
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