PRESENTATION

ON

INTERMEDIATE BAND QUANTUM DOT SOLAR CELL

S. K. Chaudhary Educational Trust’s

Shankara Institute of Technology Kukas, Jaipur (Rajasthan)

Presented by: VINEET KUMAR Electronics & communication Engg. B.Tech IV Year(VIIIth Sem)

Presented to: Mr. Rajesh Kanwadia Ms. Shweta Agarwal (Sr. Lecturer, Seminar Incharge)

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

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.

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.

ASSUMPTIONS

Only radiation recombination

One electron-hole pair per photon

Constant quasi-Fermi levels

No high energy photons in low energy processes

Maximum concentration of solar radiation

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=(EFCB - EFVB)/q V~Eg for main semiconductor

Essential for operation 3 quasi-Fermi levels

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

How can we introduce these intermediate

energy levels in the band gap?

Answer “Introduce Quantum

Dots”

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

Operational principles of IBSC

Incoming photons to base layer can cause three different transitions between valance band (VB), conduction band (CB) and IB depending on their energy:

VB→CB, if the photon energy is greater then ECV.

VB→IB, if the photon energy is greater then EVI

IB→CB, if the photon energy is greater then ECI.

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

(II) Efficiency

APPLICATIONS

Photovoltaic devices: solar cells

Light emitting diodes: LEDs

Quantum computation

Flat-panel displays

Memory elements

Photodetectors

Lasers

What limits performance of these QD IBSC?

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-band gap photons.

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

Queries