The document discusses intermediate band quantum dot solar cells. It introduces that a quantum dot consists of a semiconductor particle surrounded by a larger bandgap material, creating discrete energy levels. An intermediate band solar cell aims to absorb sub-bandgap photons using an intermediate band created by closely spaced quantum dots in a lattice. This structure could potentially increase solar cell efficiency but challenges remain around weak sub-bandgap absorption, low voltages and costs that require further research.

1. A
PRESENTATION
ON
“INTERMEDIATE BAND QUANTUM DOT SOLAR CELL”

2.  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

3.  Generations of voltage from
photons
 Light energy ( photons) are
converted into electrical
energy
( voltage).
 This conversion is called
“ photovoltaic effect”.

4.  First generation: silicon wafer-
based solar cells
 Second generation: thin-film
deposits of semiconductors
 Third generation: photo-
electrochemical cells
 Fourth generation: composite
photovoltaic technology

5.  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.

6. .

8.  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.

9.  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

11. Answer
“Introduce Quantum Dots”

12.  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.

13.  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

14. The structure is as follow :

16.  Dot sized shape, composition
 Dot spacing
 Dot regularity
 Materials
 Doping

17.  Higher Efficiency.
 Balance between the
two factors :
(I) Cost/Watt
(II) Efficiency

18.  Photovoltaic devices: solar cells
 Biology : biosensors, imaging
 Light emitting diodes: LEDs
 Quantum computation
 Flat-panel displays
 Memory elements
 Photodetectors
 Lasers

19.  Weak absorption of sub-band gap photons
 Low open-circuit voltage
 Low currents
 Cost

20.  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.

21.  Much more work needs to be done before IBSC
can
make a major contribution to the PV market.
“ Miles To Go Before I sleep”