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A New Type Of Solar Cells That Can Be Washed and Stretched

[Estimated read time: 4 minutes]
  • Scientists develop a new organic, ultrathin solar cell that can be washed and stretched by half their length. 
  • It transforms sunlight into electrical energy with 8% efficiency, while being very stable in both air and water. 
  • A few companies have shown interest in commercializing the technology. 

Developing solar panels sounds great, but washable and flexible solar cells sound even better. Scientists at RIKEN Research in Tokyo, have developed new organic, super-thin cells that can withstand 20 simulated washing cycles and can be stretched by half their length.

This is the world’s first solar cell that can deliver higher energy efficiency while maintaining stretchability and stability in air and water.

These cells could be used in textiles, network devices, recharging mobile devices on the go, powering personal health monitors, and much more. Technically, the possibilities are endless. Let’s find out how exactly scientists have built these cells and what they are capable of.

The Structure of New Solar Cells

A team of scientists at RIKEN Center for Emergent Matter Science (CEMS) developed an organic photovoltaic (OPV) – a thin organic active layer of solar cell. It transforms the light coming from the Sun into electrical energy, with 8% efficiency, while being very stable in both air and water.

The thicker organic layer could be used to achieve a maximum conversion rate of 10%, but for an OPV, which is about 1 micrometer thick, 8% is an impressive conversion rate. And because the organic material is very thin, it can be flexed without smashing.

A few months back, the same layer was used to create the solar cells, but they were not stretchable enough. The issue was later resolved by integrating stretched rubber-like elastomer sheets over the outside (like a sandwich structure). This enabled the solar cell to fold itself into an accordion-like structure with peaks and troughs.

Along with giving the cell its stretchability, the elastomer sheets are also somewhat waterproof, which makes the solar cells to withstand 20 cycles of mechanical compression in water for 1 hour and 40 minutes. The efficiency of cells decreased by only 20% after 20 washing cycles.

Organic solar cell being washed and stretched

More specifically, the study shows washable polymer solar cells with maintained high efficiency (7.9%) and stretchability (52%). The mechanically stable, ultraflexible OPVs with a total thickness of 3 micrometers are developed by combining stable active layers and inverted architecture, yielding a power conversion efficiency of up to 7.9% and showing a stable power conversion efficiency under ambient air environment (54% of initial efficiency after 1 month), and stretchability of 41%.

Reference: Nature | doi:10.1038/s41560-017-0001-3 | RIKEN Research

The degradation of efficiency was 20.8% when freestanding OPVs were dipped into water for 2 hours. The reduction was significantly suppressed to 5.4% on sandwiching the flexible OPVs between two elastomers.

Structure of the freestanding OPVs

Applications

These solar cells could be used to power electronic devices like sensors to measure body temperature, heart rate, blood pressure or electrodermal activity. There are also numerous sensor-embedded textiles. By merging these technologies with this new type of solar cells, a few smart sensor clothes systems could be developed.

In the far future, if higher voltages can be realized, these cells in clothing could be used to recharge handheld instruments like smartphones, tablets, and may be one day able to fulfill household electricity needs. If the solar cells could be integrated with lightweight and thin batteries, their effectiveness could be further improved.

The real world applications are probably 3-5 years down the track. In fact, a few companies have shown interest in commercializing the technology.

Read: Depth Sensors In Self-Driving Car Are Now 1000 Times Better

However, the two major obstacles of commercialization will be the size and cost of the solar cells. For now, they are limited to 10*10 cm, which are quite expensive to fabricate. But this is majorly down to the active layer’s cost. The sheet coating is astonishingly thin, which will eventually cut costs. So if big companies in the market decide to commercialize it, they could build a new technique to mass produce the material of active layer and decrease the cost.

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