1. Stability of PbTe Quantum Dots
Lead (II) Telluride Quantum Dots
Stability of PbTe QDs in Solution
PbTe QDs in Solar Technology
Glen Junor1, Juliette A. Micone2, Jason Tolentino2, Sam Keene3, Matt Law1,2
5.5 nm Diameter
PbTe vs PbSe in Air
Air Stable PbTe Films
Behaviors:
• Blue shifting
• Decreased Absorbance
• Loss of first exciton definition
Behaviors correspond to
uneven oxidation of QDs
Trends:
• PbTe blue shifts faster for all sizes
• PbTe peaks become
indistinguishable
What is Multiple Exciton Generation (MEG)?
Reference 2.
1. Photon is absorbed hv = n(Eg)
• Promotes “hot” Electron
2. Hot carrier undergoes MEG
• MEG is in competition with
cooling (emission of phonons)
Department of Chemistry1, Department of Chemical Engineering and Materials Science2,
Department of Physics3 at University of California, Irvine
References
Acknowledgements
Three Sizes
After Air-Exposure
Quantum Dot (QD) Solar Cells
Benefits:
• Solution Based Processing
• High absorption coefficient
• Increased theoretical solar
cell efficiency with MEG1
• 33% to 44%
• 152 nm Exciton Bohr Radius3
• Best Multiple Exciton Generation
(MEG) efficiencies2
• Labile and oxidizes easily
Electrochemical Analogues:4
• ½ O2 + 2H+ +2e-  H2O 1.23 V
• S + 2H+ +2e-  H2S 0.17 V
• Se + 2H+ +2e-  H2Se -0.37 V
• Te + 2H+ +2e-  H2Te -0.72 V
• .
Making PbTe Quantum Dots
Synthesis of all QDs was carried out using standard air-free
techniques.
3.1 nm Diameter QDs
• PbO: 0.7009 g
• Oleic Acid: 1.7 g
• 1-Octadecene:
15.78 g
Heated and Degased 1
hour
• TOPTe: 12 mL of
0.75 M
Injected into round
bottom at 140 ̊ C
React for 3 minutes
Conclusions
PbTe QD films can be made air stable by ligand exchange
with 1,2-ethanedithiol followed by infilling and over-coating
with Al2O3 by atomic layer deposition (ALD). Since the general
stability of all sizes of PbTe QDs are very similar in solution,
Al2O3 ALD will most likely work for all sizes.
Future Work
Studies on PbTe must investigate electronic characteristics of
these air stable films to predict the ideal configuration of the
final solar cell.
1. Nozik, A. Spectroscopy and Hot Electron Relaxation Dynamics in Semiconductor
Quantum Wells and Quantum Dots. Annual Review of Physical Chemistry 2001
52,193-231.
2. Stewart, J.; Padilha, L.; Bae, W.; Koh, W.; Pietryga, J.; Klimov, V. Carrier Multiplication
in Quantum Dots within the Framework of Two Competing Energy Relaxation
Mechanisms. J. Phys. Chem. Lett. 2013, 4, 2061-2068.
3. Murphy, J.;Beard, M.; Norman, A.; Ahrenkiel, P.; Johnson, J.; Yu, P.; Micic, O.; Ellingson,
R.; Nozik, A. PbTe Colloidal Nanocrystals: Synthesis, Characterization, and Multiple
Exciton Generation. J. Am. Chem. Soc. 2006, 128. 3241-3247.
4. Standard Reduction Potentials. http://www.av8n.com/physics/redpot.htm (Accessed Mar
19, 2015
5. Ihly, R.; Tolentino, J.; Liu, Y.; Gibbs, M.; Law, M. Photothermal Stability of PbS Quantum
Dot Solids. ACS Nano. 2011, 5 , 8175-8186.
6. Urban, J.; Talapin, D.; Shevchenko, E.; Murray, C. Self-assembly of PbTe quantum dots
into nanocrystal superlattices and glassy films. J. Am. Chem. Soc. 2006 128, 3248-
3255.
• University of California Leadership Excellence through Advanced Degrees
(UC LEADS)
• Daniel Fabrega
• Jason Tolentino
• Dr. Markelle Gibbs
• Dr. Matt Law
PbTe QDs in
tetrachloroethylene
PbTe QD Thin Film
3.1 nm Diameter 7.1 nm Diameter
5.5 nm3.1 nm
7.1 nm
Overall:
• PbTe is less stable in
air than PbSe
Film conditions:
• 1494 nm 1st exciton
• Spin Coat 125 nm thick
• Soak in 1,2-ethanedithiol
• Al2O3 ALD
• Infill + 20 nm overcoat
Behaviors:
• Red shift + Broadening
• No visible changes even
after 3.5 months in air!
7.1 nm Diameter QDs
• PbO: 1.5 g
• Oleic Acid: 5 g
• 1-Octadecene: 10 g
Heated and Degased 1
hour
• TOPTe: 10 mL of
1.5 M
Injected into round
bottom at 140 ̊ C
React for 3 minutes
5.5 nm Diameter QDs
• PbO: 1.5 g
• Oleic Acid: 5 g
• 1-Octadecene: 10 g
Heated and Degased 1
hour
• TOPTe: 10 mL of
1.5 M
Injected into round
bottom at 180 ̊ C
React for 30 seconds