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Nanostructured germanium holds promise for portable photovoltaics

08 December 2015

German researchers have developed a more robust material for flexible solar cells that comprises a porous germanium honeycomb-like structure.

Filled with suitable organic polymers the highly porous germanium nanofilm becomes a hybrid solar cell. Because the germanium nanostructure forms an inverse opal-structure, the material shimmers like opal (photo: Andreas Battenberg/TUM)

Using a new procedure researchers at the Technical University of Munich (TUM) and the Ludwig Maximillians University of Munich (LMU) can now produce extremely thin and robust, yet highly porous semiconductor layers. The researchers believe this is a promising material for small, lightweight, flexible solar cells or electrodes for improving the performance of rechargeable batteries.

The coating shimmers like an opal, yet it is hard as a crystal, exceptionally thin and - since it is highly porous - and light as a feather.

By integrating suitable organic polymers into the pores of the material, the scientists can tailor the electrical properties of the resulting hybrid material. The design not only saves space, it also creates large interface surfaces that improve overall effectiveness.

"You can imagine our raw material as a porous scaffold with a structure akin to a honeycomb. The walls comprise inorganic, semiconducting germanium, which can produce and store electric charges. Since the honeycomb walls are extremely thin, charges can flow along short paths," says TUM's Professor Thomas Fässler.

When combined with polymers, these porous germanium structures are suitable candidates for lightweight and flexible solar cells that can charge mobile phones, cameras and laptops while on the move.

Hitherto, organic compounds have been used in the development of flexible solar cells, which are sensitive and have relatively short lifetimes. Heat and light decompose the polymers and cause the performance to degrade. With this work, the thin but robust germanium hybrid layers provide a more robust alternative.

The researchers now want to use the new technology to manufacture highly porous silicon layers. The layers are currently being tested as anodes for rechargeable batteries and could conceivably replace the graphite layers currently used in batteries to improve their capacity.

A video animation of the material can be viewed here.

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