Using molecules to capture solar energy Timothy Schmidt.
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Transcript of Using molecules to capture solar energy Timothy Schmidt.
Using molecules to capture solar Using molecules to capture solar energyenergy
Timothy SchmidtTimothy Schmidt
The solar spectrum
1000 W/m2
Light is made of photons
hc
E Energy of photon
Planck constantSpeed of light
Wavelength
The solar spectrum
Low energy photons
High energy photons
Electrons absorb photons, get energy
E
electrons
unoccupiedenergy levels
diamond
Electrons absorb photons, get energy
E
electrons
unoccupiedenergy levels
silicon
The solar spectrum
1000 W/m2
single threshold solar cells
~32% max
electrons
unoccupiedenergy levels
V
Shockley-Queisser limit
0.5 1.0 1.5 2.0 2.5
5%
15%
25%
35%
SiGaAs
CdS
a-Si:H
CdTe
Band gap /eV
effici
ency
Ge
6000K sun limit
SQ limit
the 3 generations of solar cell
Single threshold(Shockley-Queisser limit)
ThermodynamicLimit
routes to circumventing Shockley-Queisser limit
• using the low energy photons– upconversion– intermediate band cells
• using all the photon’s energy– downconversion– multiple exciton generation– singlet Fission– hot carrier cells
Electrons have “spin”
Ground state S0 Excited state S1
Electrons have “spin”
Ground state S0 Excited state S1 Excited state T1
Molecular photophysics!
absorption
fluorescence(fast, allowed)
Molecular photophysics!
absorption
Phosphorescence(slow, forbidden)
Intersystem crossing
what is wrong with this picture?
T1
triplet-triplet annihilation (TTA)
S1
emitter
S0
emitter
sensitizer
S0
S1
T1
sensitizer
S0
S1
T1T1
S0
TTA
S1
ISCISC
Up-conversion
cell
Up-conversion unit
Limiting efficiency of an Upconversion cell is about 50%
select a sensitizer
tetrakisquinoxalinoporphyrin palladium (II)
ultrafast photoluminescenceThe compound only fluoresces while in S1 (only 10ps!)
Measured fluorescence lifetime = 5psCalculated fluorescence lifetime = 20nsFluorescence yield = 0.025%Triplet yield may be 99.975%!
select an emitter
100% fluorescence yieldused by others for TTA upconversion
TTA emission kinetics
prompt fluorescence vs upconversion
laserlaser
upconversion fluorescence
TTA yieldsmixture ref pure rubrene ref
33%
25%
Nothing wrong with this picture!
or this…
ummmm?
Dennis Cheng
Dr Nicholas J. Ekins-Daukes(NED)
Now at Imperial Collegeour man in London
Dr Raphael “femtofingers” Clady
Murad Tayebjee
$$ acknowledgements $$
University of SydneyUniversity of NSW
ARC LIEFARC DPGCEP
Application to a-Si
realistic a-Si cell100nm, 200nm or 300nm
1mm up-conversion unit
Application to a-Si
Spectra transmittedthrough cell
Modelled porphyrin absorption spectra
Application to a-Si
667 Porphyrin
Jsc Voc FF Eff
100nm 88.8 0.838 55.3% 4.1%
200nm 120 0.874 57.6% 6.1%
300nm 136 0.889 58.2% 7.1%
Bare a-Si
Jsc Voc FF Eff
100nm 84.2 0.832 54.8% 3.8%
200nm 114 0.869 57.4% 5.7%
300nm 131 0.884 58.1% 6.8%
780 Porphyrin
Jsc Voc FF Eff
100nm 89.4 0.839 55.4% 4.2%
200nm 122 0.876 57.7% 6.2%
300nm 139 0.891 58.3% 7.4%
Monster porphyrin
Jsc Voc FF Eff
100nm 105 0.859 56.8% 5.1%
200nm 141 0.893 58.4% 7.6%
300nm 160 0.906 58.8% 8.8%
+34%
