Amorphous Silicon Coated Nanowires Show Drastic Decrease in Surface Recombination

Harvard and Berkeley researchers have increased the sensitivity and efficiency of materials significantly by applying a coating to single silicon nanowires. The results recorded in Nano Letters imply that the coated wires can be used in solar cells and photodetectors.

Owing to a high surface-to-volume ratio, nanowires have a disadvantage of a high surface recombination rate. As a result, the photogenerated charges recombine instead of depositing at the terminals. The carrier time taken by a simple nanowire is reduced by four to five times in magnitude, thus reducing the efficiency of material in applications such as solar cells.

Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), Kenneth Crozier, worked with his coworkers to devise a promising solution. The team made accurate measurements on individual nanowires coated with a layer of amorphous silicon to reveal a drastic decrease in surface recombination.

Surface passivation was utilized to improve silicon chips efficiency. But, researchers have not experimented much with surface passivation of nanowires. During the creation of a collection of single-crystal silicon nanowires, the scientists discovered that the tiny particles of gold used to form the nanowires were used up. Hence, they assumed that the amorphous silicon coating was collected on each nanowire.

Crozier and his research team made a decision to test the collection of silicon nanowires. Using scanning photocurrent studies, researchers found a hundred-fold decrease in surface recombination. On the whole, the coated wires featured a 90-fold improvement in photosensitivity when compared to uncoated nanowires.

Co-author Yaping Dan claims that the increase in efficiency is due to the fact that the coating extends the broken bonds at the silicon surface. Moreover, the coating may result in a high–electric potential barrier, which restricts the movement of the photo-generated charge carriers within the single-crystalline silicon. The researchers estimate that the nanowires will offer high-energy conversion efficiency in solar cells due to improvement in carrier lifetime.

Source: http://www.harvard.edu/