Trapping light inside solar cells

[Whales]

Here's an interesting idea: etch diffraction gratings into a solar cell to try and trap the photons inside.  https://www.osapublishing.org/optica/abstract.cfm?uri=optica-7-10-1377 (openly downloadable)

Sadly it looks like all of their research is simulation -- I can't find any evidence of them actually making a test sample, despite them using the word 'etch' everywhere, and regardless they'd probably be proud enough to provide an electron photo of it if they did. 

Raw (theoretical) improvement in cell output current was over 2x.  Even a small fraction of that would be greatly appreciated.

No photon has ever escaped my prison!

[Kleinstein]

The idea with light trapping is not new. I heart of it already some 20 years ago, when I looked at solar cells.  The article here however seems to look more at getting anti reflective surface from a rough surface. The normal flat surface AR coatings are already quite good, so I don't think there is much potential here.

A structured surface has the disadvantage of additional surface recombination and thus loosing electron/hole pairs while capturing a few more photons.

It is odd looking at 1 µm range crystalline Si - normal wavers and cells are more like 200-500 µm think. Quite a low of the used light is in the red and NIR range that goes quite deep into the material and ideally is reflected from the back surface and only than trapped by no letting it out so easy.  One trouble with the trapping structures is that is that it depends on the angle of incidence. So it may help at noon and reduce the efficiency if the light come from an angle.

[f4eru]

As far as I know, texturing solar cells is commonly done on nearly all kind of cells.
It can be chemical (most common), mechanical, or laser abrasion....
This is why raw cells look glossy typically.

[Kleinstein]

I know there was a lot of ties with textured surface some 20 years ago. It helps a little against reflection, but is also has downsides as more problem with the front contacts.  So I am not sure of a textured surface is actually used. A good flat anti reflective layer is also quite good in giving the typical slightly bluish tint to the cells. The blue color comes from the AR coating getting less effective to the ends. We can't see the IR end obviously.
One can get good good performance also with a flat surface - at university I have tested a prototype cell getting around 24 % efficiency (quite close to the record mark at that time) with a standard flat surface, just clean material and a reflecting back side contact.

Light trapping may be an issue with the thinner cells, less with classical crystalline silicon.

[coppercone2]

contracting maxwells demon to stand around with a mirror?

[Kleinstein]

contracting maxwells demon to stand around with a mirror?

This is a good point: for the interface the light can go both ways, so an anti-reflective layer work both ways. Light trapping usually refers to making it hard for NIR part of the light that is no absorbed very much to get reflected back from the back of the cell and back out the front. There is no much one can do at the front, it is more to have the back side to direct the light to a different angle, so that the path is longer.

[tszaboo]

Well, I'm 50% sure, that the next big thing for solar panels will be quantum dots. To convert parts of the spectrum to other color, where the cell can work with higher efficiency.

[coppercone2]

well it says they reflect 2% of light, so there is not much gain to be made here