Transcript Solar Energy Conversion - UNT College of Arts and Sciences

Some applications related to Chapter 11 material:
We will see how the kind of basic science we discussed in
Chapter 11 will probably lead to good advances in applied
areas such as:
1- Design of efficient solar cell dyes based on charge transfer
absorption.
2- Strongly luminescent materials based on the Jahn-Teller
effect.
1- Design of efficient solar cell dyes
based on charge transfer absorption
COO-
COO-
PO3-
PO3-
N
N
N
N
diimine
Pt
Pt
S
S
S
S
dithiolate
These complexes should have charge transfer from metal or ligand
orbitals to the p* orbitals.
CT-band for Pt(dbbpy)tdt
S
N
Pt
N
S
Data from: Cummings, S. D.; Eisenberg, R. J. Am. Chem. Soc. 1996, 118 1949-1960
X- Chloride
X-thiolate
dx2-y2
p*bpy
hv
CT to diimine
{
p (thiolate)
+
d p (Pt)
dxy
dxz-yz
dxz+-yz
dz2
Connick W. B.; Fleeman, W. L. Comments on Inorganic Chemistry, 2002, 23, 205-230
p bpy
70,000
500
N
60,000
S
S
S
450
O
400
e , M-1 cm-1 (NIR)
Pt
N
e , M-1 cm-1 (UV/VIS)
S
50,000
350
300
40,000
250
30,000
200
150
20,000
100
10,000
50
0
200
0
300
400
500
600
700
800
900 1000 1100 1200 1300 1400 1500 1600
Wavelength, nm
Electronic absorption spectra for dichloromethane solutions of (dbbpy)Pt(dmid), 1, (thin line) and
[(dbbpy)Pt(dmid)]2[TCNQ], 3, (thick line) in the UV/VIS region (left) and NIR region (right).
Smucker, B; Hudson, J. M.; Omary, M. A.; Dunbar, K.; Inorg. Chem. 2003, 42, 4717-4723
Pt(dbbpy)tdt in Dichloroethane
1
0.9
70mg/10mL stock
1ml-2ml
0.5ml-2ml
1:10ml
1:100ml
1mlof 1/100 -2
0.5ml of 1/100-2
1:1000ml
0.8
0.7
Abs.
0.6
0.5
0.4
0.3
0.2
0.1
0
250
350
450
550
650
750
Wavelength (nm)
850
950
1050
By Brian Prascher,
Chem 4610 student, 2003
LUMO
hv
HOMO
Clearly a dx2-y2
orbital, not a
diimine p*
So the lowest-energy NIR bands are d-d transitions and the LUMO is indeed dx2-y2, not diimine p*
MO diagram for the M(diimine)(dithiolates) class!!!
dx2-y2
p*bpy
p*bpy
dx2-y2
{
p (thiolate)
+
d p (Pt)
{
p (thiolate)
+
d p (Pt)
dxy
dxz-yz
dxz+-yz
dz2
p bpy
WHO CARES!!
The above was science, let’s now see
a potential application
• Silicon cells
– 10-20 % efficiency
– Corrosion
– Expensive (superior crystallinity required)
• Wide band gap semiconductors (e.g. TiO2;
SnO2; CdS; ZnO; GaP):
– Band gap >> 1 eV (peak of solar radiation)
– Solution: tether a dye (absorbs strongly across
the vis into the IR) on the semiconductor
– Cheaper!!… used as colloidal particles
Literature studies to date focused almost solely on dyes of Ru(bpy)32+
derivatives ==> Strong absorption across the vis region
(Grätzel; Kamat; T. Meyer; G. Meyer; others)
[M(N3)(X)]+Y- where M = Pt(II), Pd(II) or Ni(II); N3=triimine; X = anionic ligand (SCN, halide, RS-, etc.).
+
t-Bu
t-Bu
N
N Pt N
t-Bu
Y-
X
ArS- group
Y= Cl-, BF4-, TCNQ-
Na+
Na+
-
Sodium thiophenoxide
N
N
S
S
4-methylbenzenethiol sodium salt
mbt
PhS
SH
SH
N
N
O
O
7,7,8,8-Tetracyanoquinodimethane
TCNQ
3,4-methylbenzenethiol
dmbt
2,5-dimethoxythiophenol
dmeobt
Absorption Spectra of [Pt(tbtrpy)X]+ Y- Complexes
Normalized absorbance
Cl,Cl
37 9 39 9
SCN,BF4
PhS,BF4
55 1.5
SCN,TCNQ
85 1
75 0
350 400 450 500 550 600 650 700 750 800 850 900 950 1000
Wavelength, nm
• Using ArS- ligands as X shifts the CT absorption to the VIS region.
•Using TCNQ- as Y adds NIR absorptions.
2- Strongly luminescent materials
based on the Jahn-Teller effect
a1'
p
e'
a2''(pz)
6p 0
6s0
e'(dxy,dx2-y2)
e''(dxz,dyz)
a1'(dz2)
5d10

[Au] +
(5d10)
[Au(PR3)3]+
PR3
Ground-state MO diagram of [Au(PR3)3]+ species, according to
the literature:
Forward, J.; Assefa, Z.; Fackler, J. P. J. Am. Chem. Soc. 1995, 117, 9103.
McCleskey, T. M.; Gray, H. B. Inorg. Chem. 1992, 31, 1734.
By Khaldoon Barakat,
Chem 5560 student, 2002
Molecular orbital diagrams (top) and optimized structures (bottom) for the 1A1’ ground state (left)
of the [Au(PH3)3]+ and its corresponding exciton (right).
Barakat, K. A.; Cundari, T. R.; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 14228-14229
lem= 496 nm
lem= 478 nm
lem= 640 nm
[Au(TPA)3
]+
lem= 772 nm
QM/MM optimized structures of triplet [Au(PR3)3]+ models.
Barakat, K. A.; Cundari, T. R.; Omary, M. A. J. Am. Chem. Soc. 2003, 125, 14228-14229
WHO CARES!!
The above was science, let’s now see
a potential application
RGB bright emissions in the solid state and at RT are
required for a multi-color device….
AuL3 as LED materials?
• Glow strongly in the solid state at RT.
• But [Au(PR3)3]+ X- don’t sublime into
thin films (ionic).
• How about neutral Au(PR3)2X?:
– Do they also luminesce in the solid state at
RT?
– Do they also exhibit distortion to a T-shape?
T-shape and BEYOND!
154.1º;
138.4º
(132.1º)
191.8º;
188.7º
hv
102.4º; 103.5º;
115.5º
106.2º
(109.2º) (118.7º)
83.6º;
85.1º
84.7º;
85.1º
Au(PPh3)2Cl. Bond angles shown are: B3LYP; HF (exptl.).
“Photocrystallography” and time-resolved EXAFS should
tell us if these distortions toward and beyond a T-shape
will really take place experimentally…stay tuned!
* The lifetime (7.9 ms) suggests that the emission is phosphorescence from a formally triplet excited state.
Photoluminescence spectra of Au(PPh3)2X
Excitation
Emission
X=I
300
350
400
X=Br
450
500
X=Cl
550
Wavelength, nm
600
650
700