Promising power source for wearable electronics

Researchers from Kyung Hee University and electronics giant Samsung in Korea have devised a textile-based organic photovoltaic cell that they believe could be a promising approach for powering wearable electronics [S. Lee et al., Nano Energy 9 (2014) 88–93, DOI: 10.1016/j.nanoen.2014.06.017].

Organic photovoltaics (OPV) cells are an attractive option for applications because of their unique properties, which include flexibility, light weight, easy processability, low cost, and environmental friendliness. These attributes make OPVs ideally suited to emerging applications like smart watches or Google glasses. Most devices to date have been based on flexible film-based OPV cells, but there is a now a drive for textile-based systems to power other wearable electronic devices. Such OPV cells could be integrated into clothes, bags, or even tents to power essential items like cell phones, tablets or other devices.

The researchers, led by Dukhyun Choi of Kyung Hee University and Jongjin Park from Samsung, have designed and fabricated a textile-based OPV that can be stitched into clothing. The device itself is comprises an indium tin oxide (ITO) bottom electrode, a ZnO electron transport layer, a P3HT:PCBM (poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester fullerene) bulk heterojunction photoactive layer, and an MoO3 hole transport layer. Finally, a thin Ag layer can be deposited as a top electrode or the entire device can be mounted on an Au textile electrode instead.

The textile electrode the researchers demonstrate is woven from multilayered fibers comprising a PET core coated with Ni-Cu-Ni layers and an outer Au coating. The fibers can be woven into large area textile electrodes of around 5 cm2. Since the woven fibers create a surface that is uneven rather than completely smooth, the researchers believe that it could enhance photoabsorption and provide a higher current density.

The textile-based device can be readily stitched into fabric or clothing, say the researchers. The devices also appear to be quite durable and able to withstand repeated bending and flexing.

There is still plenty of room for improvement, however. The textile-based OPV devices have rather low power conversion efficiencies (PCEs) of 1.79%. The team believes that this could be increased by improving contacts in the device structure and removing air gaps. The relatively high short circuit current density of the textile-based device compared with a typical OPV is promising though. Choi and Park suggest that their approach could open the way for effective textile-based solar cells for next-generation wearable electronics.

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