Scientists discover photovoltaic nanotubes

Authored by pv-magazine-australia.com and submitted by mvea

Scientists investigating various functions for a semiconductor nanotube have discovered one such material – made from tungsten disulfide – exhibits the bulk photovoltaic effect (BPVE) at an efficiency far higher than in other materials known to exhibit the phenomenon. BPVE occurs when a current is generated throughout the entire structure of a material rather than relying on a junction between materials.

“Essentially our research material generates electricity like solar panels but in a different way,” said University of Tokyo professor Yoshihiro Iwasa. “We demonstrated for the first time nanomaterials could overcome an obstacle that will soon limit current solar technology.”

Tungsten disulfide only exhibits a photovoltaic effect when rolled into nanotubes. The bulk photovoltaic effect occurs because the nanotube is not symmetrical and the current generated has a preferred direction to flow in. Other materials with a similar ‘broken inversion symmetry’ structure have been shown to exhibit BPVE but Iwasa and his team found that with tungsten disulfide nanotubes, the conversion efficiency was much higher than previously observed.

“Our research shows an entire order of magnitude improvement in efficiency of BPVE compared to its presence in other materials,” Iwasa said. The study has been published in Nature.

In theory, BPVE could provide scientists with a route to higher efficiency solar cells. However, the efficiencies observed so far are too low to move beyond the lab. Iwasa also noted, scaling up the nanotube to a relevant size represents a significant challenge.

gingerbread_man123 on August 30th, 2019 at 23:06 UTC »

Interesting how people are pointing out the very clear and obvious problems (which are valid problems) but not seeing beyond them.

Some of the problems: Difficult to scale up Alignment of tubes in bulk is a challenge

However, this is front end research - blue sky fundamentals - they aren't saying they can spin this off directly, but the concepts can be applied to other similar materials that may prove easier to scale and arrange, or to existing materials to improve their output.

Hundreds of teams of researchers in the field will read the article, and do everything from make minor tweaks to their own work to start new projects based on this.

In the end, is this particular team likely to end up with a real world product based on this material, maybe not (but not impossible!). But is their work likely to influence others that will, very likely.

Fucking-Usernames on August 30th, 2019 at 21:24 UTC »

So, why this will not work and why I'm an idiot for having hopes of it working?

mvea on August 30th, 2019 at 20:35 UTC »

The title of the post is a copy and paste from the subtitle of the linked academic press release here:

An international team of researchers led by the University of Tokyo has discovered a new material which, when rolled into a nanotube, generates an electric current if exposed to light. If magnified and scaled up, say the scientists, the technology could be used in future high-efficiency solar devices.

Journal Reference:

Enhanced intrinsic photovoltaic effect in tungsten disulfide nanotubes

Y. J. Zhang, T. Ideue, M. Onga, F. Qin, R. Suzuki, A. Zak, R. Tenne, J. H. Smet & Y. Iwasa

Nature, volume 570, pages349–353 (2019)

Link: https://www.nature.com/articles/s41586-019-1303-3

DOI: https://doi.org/10.1038/s41586-019-1303-3

Abstract

The photovoltaic effect in traditional p–n junctions—where a p-type material (with an excess of holes) abuts an n-type material (with an excess of electrons)—involves the light-induced creation of electron–hole pairs and their subsequent separation, generating a current. This photovoltaic effect is particularly important for environmentally benign energy harvesting, and its efficiency has been increased dramatically, almost reaching the theoretical limit1. Further progress is anticipated by making use of the bulk photovoltaic effect (BPVE)2, which does not require a junction and occurs only in crystals with broken inversion symmetry3. However, the practical implementation of the BPVE is hampered by its low efficiency in existing materials4,5,6,7,8,9,10. Semiconductors with reduced dimensionality2 or a smaller bandgap4,5 have been suggested to be more efficient. Transition-metal dichalcogenides (TMDs) are exemplary small-bandgap, two-dimensional semiconductors11,12 in which various effects have been observed by breaking the inversion symmetry inherent in their bulk crystals13,14,15, but the BPVE has not been investigated. Here we report the discovery of the BPVE in devices based on tungsten disulfide, a member of the TMD family. We find that systematically reducing the crystal symmetry beyond mere broken inversion symmetry—moving from a two-dimensional monolayer to a nanotube with polar properties—greatly enhances the BPVE. The photocurrent density thus generated is orders of magnitude larger than that of other BPVE materials. Our findings highlight not only the potential of TMD-based nanomaterials, but also more generally the importance of crystal symmetry reduction in enhancing the efficiency of converting solar to electric power.