Nanowires Make Bendy Solar Cells

Researchers at the A*STAR Institute of Microelectronics in Singapore, led by Chang-yun Jiang, have developed highly bendable “dye-sensitized” solar cells made from zinc oxide nanowire photoelectrodes on plastic substrates. The researchers found that the nanowires are highly resistant to cracking because gaps between the nanowires allow them to efficiently release bending stresses. The devices, which conserve their photovoltaic properties even when they are extremely bent, have a variety of potential application in flexible and portable devices, such as solar-cell mobile phone chargers, clothes, and umbrellas.

 Bendy nanowires (Credit: Singapore National Electronics Sector)
Bendy nanowires (Credit: Singapore
National Electronics Institute)

The photoanodes in dye-senzitised solar cells (DSCCs) are usually made from a film of titanium dioxide or zinc oxide nanocrystals. The problem is that these thick films are fragile and crack easily when bent. Moreover, nanocrystals work well at high temperatures, which are disastrous for the plastic-film substrates. The scientists solved this problem by creating flexible DSSCs that are based on this substrate, so that their properties are conserved even when bent. 

Jiang and his colleagues grew the zinc oxide nanowire film on a transparent plastic indium tin oxide (ITO) substrate and immersed the zinc oxide film in a ruthenium dye solution to make the working electrode. They then prepared a flexible counter electrode by electron-beam coating a 50 nm platinum layer on another plastic substrate. The flexible cell was completed by bonding the nanowire working electrode and the platinum counter electrode together, ensuring that a gap of 50 micron was left between the two so that a liquid electrolyte could be poured into the device.  

Bendable nanowires in different resolutions (Credit:Singapore National Electronics Institute)
Bendable nanowires in different resolutions (Credit:Singapore National
Electronics Institute)

When sunlight reaches the cell the dye absorbs the light and excites the electrons, which inject into the zinc oxide and then transfer to the ITO electrode via the nanowires. These electrons subsequently pass through the external circuit to arrive at the counter electrode where they pass into the electrolyte, explained Jiang. 

The researchers say that this process is low cost and could be scaled up to mass-production of flexible DSSCs. The Singapore team now plans to further improve the light-to-electric power conversion efficiency and develop larger flexible DSSCs. 

TFOT recently covered a new method that doubles solar cells efficiency, which was developed by scientists from the University of Washington. TFOT has also reported on a number of other innovative solar power technologies, such as the “nano-flakes”, a newly discovered crystalline material that can efficiently convert almost twice the amount of solar energy into electricity than conventional solar panels. You can also read about EnviroMission’s solar tower project, which is designed so supply more than 200,000 typical Australian homes with enough power so that they will be powered solely by solar electricity within five years.  

More about the zinc oxide nanowire flexible cells can be found here (translated via Google).