The idea that LEDs can act as light detectors as well as emitters is well known. Now researchers at UCLA are looking at LCDs with an eye toward using them to produce electric energy in addition to functioning as your smartphone display.
The UCLA engineers have created a novel concept for harvesting and recycling energy for electronic devices — one that involves equipping these devices’ LCD screens with built-in photovoltaic polarizers, allowing them to convert ambient light, sunlight and their own backlight into electricity.
The UCLA Engineering team created a new type of energy-harvesting polarizer for LCDs called a polarizing organic photovoltaic, which can potentially boost the function of an LCD by working simultaneously as a polarizer, a photovoltaic device and an ambient light or sunlight photovoltaic panel.
Via PhysOrg.
So let me get this straight…
They’ll put a photovoltaic layer on top of an LCD, thus blocking part of the light coming from the LCD and reducing its efficiency, in order to generate energy using that same photovoltaic layer. Somehow, i doubt the net energy will be positive, but what do i know :)
They’re not placing a new layer on top of the LCD, they’re replacing an already existing layer. Existing polarizers would convert the blocked light to heat, this new polarizer will convert the blocked light to electrical energy. The linked article gives more information on how this works and how it would improve the efficiency of the displays.
Okay, but there’s still one tiny niggle…
Existing polarizers on the top of twisted nematic displays actually blocks (most of) the light only above black pixels. That’s the whole idea behind TN – light from the backlight is polarized in one direction, then repolarized or not repolarized in the perpendicular direction, thus exiting or not exiting the top (front) polarizer.
What i’m aiming at is this – the actual savings with a photovoltaic polarizer would be heavily dependent on the images displayed. Doing heavy browsing? You won’t save much. Have a black wallpaper? You’ll save more.
I’m wondering about one thing, though… How’s the efficiency affected by the direction of the light entering the layer. I.e. is its eta the same for both, ambient light and backlight, or better in one or the other direction. Also, most photovoltaics tech is most efficient and most sensitive in one tight band of the spectrum (usually UV). Wonder what the spectral response of this layer is…
Oh, and one more thing…
Modern display polarizers are reflective.
Meaning they don’t turn (most) of the light into heat (i.e. absorb light), but reflect it back into the LCD matrix.
The recovery of energy from the backlight seems a lot less interesting than the generation of energy from external light.
Honestly though, I’d settle for a conventional photovoltaic panel on the back of the phone where it doesn’t cover up the screen. That should be doable now with about zero research.
Not sure I get the whole ‘lets make panels that cover up the screen’ thing when the rest of the phone is still just plain old plastic.
Like this guy?
http://www.gsmarena.com/samsung_s7550_blue_earth-review-394.php