I generation cells : Si

II generation: thin film cellsIII generation cells: beyond the Q-S limit

more bands absorbing the light

tandem cells, intermediate band cells

low dimentional structures

more energy from one photon

hot carriers, impact ionisation

1

hot carriers, impact ionisation

transformation of sunlight

UP and DOWN conwerters

More bands:

multijunction „tandem” cells

2after J. Nelson

for 3 junctions ηηηηmaxmaxmaxmax = 63 % (under max concentration)= 63 % (under max concentration)= 63 % (under max concentration)= 63 % (under max concentration)

Record tandem cells

GaInP/GaAs/InGaAs

3

GaInP/GaAs/Ge; η=37.3 %

(under concentrated light)

η = 33.78 % (1 Sun)

NREL 2007

World present record 44% (942x)

A-SLAM technology (Solar Junction)

(Adjustable Spectrum Lattice Matched)

Multijunction structure (tandem cell)

„tandem cells”

4

Intermediate band cell

5

maximum maximum maximum maximum ηηηη=63 %=63 %=63 %=63 %

EEEEg1g1g1g1=1.93 eV=1.93 eV=1.93 eV=1.93 eV

EEEEg2g2g2g2=0.7 eV=0.7 eV=0.7 eV=0.7 eV

(ZnMn)Te:O

„tandem” cell intermediate band cell

6

maximum maximum maximum maximum η η η η ≅≅≅≅ 63 %63 %63 %63 %

More bands: quantum wells

additional absorption onadditional absorption onadditional absorption onadditional absorption on

7

additional absorption onadditional absorption onadditional absorption onadditional absorption on

energy levels in quantum wellsenergy levels in quantum wellsenergy levels in quantum wellsenergy levels in quantum wells

high energy carriers colected before high energy carriers colected before high energy carriers colected before high energy carriers colected before

thermalisation by energythermalisation by energythermalisation by energythermalisation by energy----selective contacts selective contacts selective contacts selective contacts

(tunneling junctions?)(tunneling junctions?)(tunneling junctions?)(tunneling junctions?)

More energy:

hot carriers cells

8cooling slower in quantum dots?

More energy from one photon:impact ionization

9

1 photon1 photon1 photon1 photon more than 1 electronmore than 1 electronmore than 1 electronmore than 1 electron----hole pairhole pairhole pairhole pair

observed in Si, Ge in PbSe

Impact ionisation in QD

10

up and down converters

11

Quantum dot solar cells

12

Quantum dots

13

PbS QD NREL 4%, Univ Toronto 7%

CdSe QD + TiO2

Quantum dots:

enhancement of photoexcitation spectrum

14

InAs/GaAs doped QD

Challenges and strategies in photovoltaics

15