Researchers Develop Breakthrough Transparent Solar Cells with Superior Efficiency

• Researchers develop energy-efficient transparent solar cells using silicon microwire composites.
• In addition to absorbed sunlight, these solar cells also utilize reflected rays to produce energy. 

In recent years, the floodgates of research focusing on transparent solar cells have been opened by scientists who believe solar energy can fulfill society’s demands, and it could be the next big thing.

In this interesting phenomenon of photovoltaics, there is an inevitable trade-off between light admission (visible transparency) and energy generation (photovoltaic conversion efficiency).

So far, we have seen various tinted transparent solar cells with low energy efficiency and modest transparencies. They are not suitable to be deployed in electronic devices, automobile windows, and building-integrated photovoltaic windows.

Now researchers at Ulsan National Institute of Science and Technology in South Korea have developed energy-efficient transparent solar cells using silicon microwire composites. They have embedded cylindrical silicon rods in a flexible, transparent polymer material.

How Is It Different From Other Transparent Solar Cells?

Unlike existing transparent solar cells, which are primarily based on dyes, organics, and perovskites, the new flexible, color-neutral solar cells are based on the pattern of n-silicon microwires.

The method called deep-reactive ion etching is used to fabricate these microwires with controllable spacing. They are then embedded in a flexible transparent polymer matrix.

Reference: Light: Science & Applications volume | DOI:10.1038/s41377-019-0234-y | UNIST

It is designed in such a way that reflected sunlight from the silicon rods can be controlled to increase efficiency. More specifically, the light transmittance can be adjusted from 10 to 55 percent by changing the spacing between microwires.

How Does It Work? 

Each silicon rod in this solar cell works as a photoactive layer: it absorbs sunlight and generates electricity. Researchers have arranged the rods at specific intervals so that they cannot be seen with the naked eye. Therefore, solar cells maintain both flexible and transparent characteristics of the substrate itself.

The fabrication process of the new transparent solar cell | Courtesy of researchers 

To increase light absorption capability without compromising with transparency, researchers altered the shape of the silicon microwires’ tip dramatically. While absorption, transmission, and reflection of light occur in conventional solar cells, they do not take advantage of the reflected light.

The new structure, on the other hand, absorbs the reflected light back into the solar cell: Sunlight reflected from the top of the silicon rod is absorbed by the rod next to it.

The transparent solar cells based on the slanted-tip microwires have shown 8% efficiency at visible transparency of 10%. This is the highest efficiency achieved among silicon-based transparent solar cells. They can maintain their initial efficiency even after dozens of bending tests.

Read: Global Warming Will Reduce The Efficiency of Solar Cells

And unlike other neutral-color transparent solar cells, which are manufactured on rigid glass substrates, these flexible solar cells could have various real-world applications, ranging from mobile and wearable devices to building-integrated power generation.