JAGANNATH GUPTA INSTITUTE OF ENGINEERING AND TECHNOLOGY

A

PRESENTATION

ON

“INTERMEDIATE BAND QUANTUM DOT SOLAR CELL”

CONTENTS Photovoltaic Conventional solar cell

Introduction Working Limitations

Energy bands in solids Intermediate band solar cell Quantum dot Intermediate band quantum dot solar

cell Introduction Construction Working Advantages Applications Limitations

Introduction to Photovoltaic

Generations of voltage

from photons

Light energy ( photons)

are converted into

electrical energy

( voltage).

This conversion is called

“ photovoltaic effect”.

Photovoltaic Generations

First generation: silicon

wafer-based solar cells

Second generation: thin-

film deposits of semiconductors

Third generation: photo-

electrochemical cells

Fourth generation:

composite photovoltaic

technology

Solar Cell

The solar cell (or photovoltaic cell) is a device that converts light energy into electrical energy.

Fundamentally, the device needs to fulfill only two functions:

1. Photo-generation of charge carriers (electrons and holes) in a light-absorbing material.

2. Separation of the charge carriers to a conductive contact that will transmit the electricity.

How Classical Solar Cells Operate ?

.

Energy band in crystals

Intermediate band solar cell

The intermediate band (IB) is an electronic band located within the semiconductor band gap, separated from the conduction and the valence band by a null density of states.

Intermediate band solar cells (IBSCs) are photovoltaic devices.

Used to exploit the energy of below band gap energy photons.

Intermediate band Requirements

Higher photocurrent Higher efficiency arising from

absorption of 2 sub-band gap photons to create one electron-hole pair.

High voltage V=(EF,CB- EF,VB)/q

V~Eg for main semiconductor

Essentials for operation 3 quasi-Fermi levels

IB “disconnected” from emitters Need IB half-filled with electrons Non-overlapping absorption coefficients

Energy levels

How can we introduce these intermediate

energy levels in the band gap?

Answer “Introduce Quantum

Dots”

Quantum dots

A quantum dot is a nano meter sized particle of a low band gap material surrounded by a material with larger band gap.

“Artificial atom” with energy levels depending on the dot size and on the band gap difference.

If many quantum dots are placed closed to each other in a lattice one or more intermediate bands can be formed and a new semiconductor with tailored properties has been made.

Quantum Dot

A quantum dot is a portion of matter (e.g., semiconductor) whose excitons are confined in all three spatial dimensions.

Quantum dots have properties combined between

Those of bulk semiconductors

Those of atoms

Physical structure

The structure is as follow :

Quantum Dot : Types

Salient characteristics of QDs for IBSC

Dot sized shape,

composition

Dot spacing

Dot regularity

Materials

Doping

ADVANTAGES

Higher Efficiency. Balance between

the two factors :

(I) Cost/Watt

(II) Efficiency

APPLICATIONS

Photovoltaic devices: solar cells

Biology : biosensors, imaging

Light emitting diodes: LEDs

Quantum computation

Flat-panel displays

Memory elements

Photodetectors

Lasers

What limits performance of these QD IBSC?

Weak absorption of sub-band gap

photons

Low open-circuit voltage

Low currents

Cost

Conclusions

QD SL cells show photo responses extended to longer wavelengths than GaAs control cells, demonstrating current generation from the absorption of sub-bandgap photons.

IBSC theoretically offers a way to significantly increase cell efficiency compared to that of a single-junction solar cell.

Conclusions

Much more work needs to be done before IBSC can

make a major contribution to the PV market.

“ Miles To Go Before I sleep”

Queries