A Reduction Pathway in the Synthesis A Reduction Pathway in the - - PowerPoint PPT Presentation

A Reduction Pathway in the Synthesis A Reduction Pathway in the Synthesis

• f PbSe Nanocrystal Quantum Dots

y

Jin Joo,1 Jeffrey M. Pietryga,2 John A. McGuire, 2 Sea-Ho Jeon, 2 Darrick J. Williams, 2 Hsing-Lin Wang, 2 and Victor I. Klimov*,2

1Department of Applied Chemistry, Kyungpook National University 2Chemistry Division and Center for Integrated Nanotechnologies,

Los Alamos National Laboratory, Los Alamos, New Mexico 87545

The 7th KOREA-U.S. NANOFORUM

Theoretical limit of solar cells using CM

■ T diti l l ll Slowered relaxation and cooling (~10X) of photogenerated hot e- and h+. ■ Traditional solar cell

ηmax = 31%

• W. Shockley and H. J. Queisser

■ Carrier multiplication based solar cell

• J. Appl. Phys.1961, 32, 510.

p

ηmax > 60%

S K l di ki J H W H J 2

• S. Kolodinski, J. H. Werner, H. J.

Queisser Solar En. Mat. & Sol. Cells 1994, 33, 275.

Why PbSe QDs ?

Band gap energy of 0.26 eV. Larger Bohr radius of PbSe compared to other semiconductor. PbSe 23 nm vs. CdSe 1.5 nm 8-fold degeneracy at the lowest electronic state. Highly efficient Carrier Multiplication (CM).

P ti th d Preparation methods

Low production yield ~ 5%. Efficiency of CM depends on synthesis prep. Hard to control size (too fast growth rate).

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Structure of NQDs solar cell

Si

Aluminum A

a-Si PbSe QDs

ITO

A

ITO Glass 3

• 2

Wavelength (nm)

• 4
• 3
• 3.5
• 3
• 2.5
• 2

500 1000 1500 2000

PbSe NQDs

eV) ITO Al

• 6
• 5

PbSe

+ +

5 5

• 5
• 4.5
• 4

Energy (e

• 7

PbSe QDs a-Si

• 6.5
• 6
• 5.5

a-Si

4

Band edge shift was calculated from effective approximation.

Reduction pathway using HDD

(RaCOO)2Pb + Se=TOP → [PbSe] + O=P(Rb)3 + (RCO)2O :Too Slow Impurity in TOP (P(octyl)3) (

a

)2 [ ] ( )3 ( )2 (RaCOO)2Pb + PH(Rc)2 → [Pb0] + O=PH(Rc)2 + (RaCO)2O [Pb0] + Se=P(Rb)3 → [PbSe] + P(Rb)3 :Too fast

• J. S. Steckel et al. J. Am. Chem. Soc. 2006, 128, 13032.

(RaCOO)2Pb + HDD → [Pb0] +HCR + HCH + 2RaCOOH O= O= (RaCOO)2Pb HDD [Pb ] HCR HCH 2RaCOOH [Pb0] + Se=P(Rb)3 → [PbSe] + P(Rb)3 C O Pb(OR)2 OH OH

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C O HDD (hexadecanediol)

• J. Joo et al., J. Am. Chem. Soc., 2009, 131, 10620.

OH

Effect of HDD on PbSe synthesis

Chemical Yield Growth rate Photoluminescence QY High chemical yield up to ~ 100%. Easy preparation bigger NQDs. Controllable growth rate. Narrow size distribution within 5%

6

6

50 nm

Numerical simulation procedure

Generation of monomers

HDD Pb(II) + Se [PbSe]monomer HDD [PbSe]monomer [PbSe]Nucl.

Nucleation

Repeat ~100,000 times

Particle growth and dissolution

Particle growth

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• D. V. Talapin et. al. J. Phys. Chem. B, 2001, 105, 12279.

S.Kwon et. al. J. Am. Chem. Soc., 2007, 129, 12571.

HDD effect on QDs growth dynamics

120 140

%)

8 12 16 ical Yield (%)

Experiment

40 60 80 100

emical yield (%

1 2 3 4 Chemi Radius (nm)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 20

Che Radius (r*)

Simulation

2 5 3.0

[HDD]/[Pb] = 1 [HDD]/[Pb] = 0

Simulation

Radius (r ) 1.5 2.0 2.5

ius (r*)

2.4

[HDD]/[Pb] 0

• HDD produces substantial amount of monomer

in nucleation step.

• Fast nucleation when HDD was used.

0.5 1.0

Rad

0 100 200 300 400500 600 0.8 1.2 1.6 2.0 Radius (nm)

Experiment

• Sharp nucleation constructs the condition

for high chemical yield and QY.

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0.0 0.5 1.0 1.5 2.0 2.5 0.0

Time (τ)

0 100 200 300 400500 600

Time (s)

Conclusions

High chemical yield and precise size control can be achieved by introducing HDD a s a reducing agent. High quantum yield can be achieved by using HDD. Numerical simulation exactly describes nucleation and growth mechanism of QDs.

Acknowledgement

• Dr. John McGuire
• Dr. Victor I. Klimov
• Dr. Jeff Pietryga

This work was supported by the Chemical Sciences, Biosciences, and Geosciences Division

• f the Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

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