High efficiency Solar cellsusing

Quantum Dot Luminescent Solar

ConcentratorsA BRAIN CHILD OF

UC BERKELEY / UNIVERSITY OF ILLINOIS

Terms to be acquainted with before proceeding

Quantum DotQuantum ConfinementLuminophoreStokes shiftConcentrators

An Introduction to Quantum Dot Technology

A quantum dot is a semiconductor nanostructure that confines the motion of conduction band electrons, valence band

holes, or excitons (bound pairs of conduction band electrons and valence

band holes) in all three spatial directions.

Quantum Confinement

Quantum Confinement

Luminophore The lights in this room, the TV at home and the

mobile screens we use everyday and LEDs work on the concept of luminophores.

It’s basically a functional group that causes luminescence or illumination when exposed to a certain electrical or optical stimulus.

The use of luminophore is essential in increasing efficiency. The technology which uses this in Solar cells is called Luminescent Solar Collectors. (LSC)

Stokes Shift

LSC WORKINGA luminescent solar concentrator (LSC) is a

device that uses a thin sheet of material to trap solar radiation over a large area, before directing the energy (through luminescent emission) to cells mounted on the thin edges of the material layer.

Because of the phenomenon called Stokes shift, the blue high energy light is re-emitted as red light with more than 80% conversion efficiency and minimum losses.

Use of Luminophores in High efficiency Solar Cells

Current solar cell technology -> High area -> Greater collection

LSC -> Same area -> Re-emitted radiation concentration-> Greater collection

Hence LSC uses the same area to a greater efficiency Coupling that with concentration on a small PV cell

increases the efficiency of the solar cell on a whole.

Current experiment @UC Berkeley

By combining designer quantum dot light-emitters with spectrally matched photonic mirrors they created solar cells that collect blue photons at 30 times the concentration of conventional solar cells. With a sufficient concentration factor, only small amounts of expensive III−V photovoltaic materials are needed to collect light from an inexpensive luminescent waveguide.

They replaced the molecular dyes in previous LSC systems with core/shell nanoparticles composed of cadmium selenide (CdSe) cores and cadmium sulfide (CdS) shells that increase the Stokes shift while reducing photon re-absorption.

The CdSe/CdS nanoparticles enabled them to decouple absorption from emission energy and volume, which in turn allowed to balance absorption and scattering to obtain the optimum nanoparticle. The use of photonic mirrors that are carefully matched to the narrow bandwidth of the quantum dot luminophores achieved waveguide efficiency exceeding the limit imposed by total internal reflection.”

Added advantage: Transparency!The use of a Luminescent Solar concentrator allows the

use of organic dyes to trap light within a given boundary.This way the light can be directed by Total Internal reflection onto a Solar cell.So basically the light falling on a flat surface can be directed at its edges. Imagine your windows collecting the light and sending it to the solar cells at the edges! And the use of organic dyes can cause a transparent waveguide to form.