Efficiency limits

Efficiency limits






one electron-hole pair per photon carriers in thermal equilibrium with the lattice

η=33%

only one loss mechanism: radiative recombination Shockley i Queisser 1961

1

I generation cells : Si II generation: thin film cells III generation cells: beyond the limits more bands absorbing the light tandem cells, intermediate band cells low dimentional structures more energy from one photon hot carriers, impact ionisation transformation of sunlight UP and DOWN conwerters

2

More bands: multijunction „tandem” cells

for 3 junctions ηmax = 63 %

after J. Nelson

3

Record tandem cells GaInP/GaAs/InGaAs

GaInP/GaAs/Ge; η=37.3 %

η = 33.78 % (1 Sun) NREL 2007

(under concentrated light) 4

„tandem cells” Multijunction structure (tandem cell)

5

6

Intermediate band cell

maximum η=63 % Eg1=1.93 eV Eg2=0.7 eV (ZnMn)Te:O

7

„tandem” cell

intermediate band cell

maximum η ≅ 63 %

8

More bands quantum wells and quantum dots

additional absorption on energy levels in quantum wells

9

More energy: hot carriers cells high energy carriers colected before thermalisation by energy-selective contacts (tunneling junctions?)

cooling slower in quantum dots?

10

More energy from one photon: impact ionization

1 photon observed in Si, Ge

more than 1 electron-hole pair in PbSe 11