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Stability of PbTe Quantum Dots Lead (II) Telluride Quantum Dots Stability of PbTe QDs in Solution PbTe QDs in Solar Technology Glen Junor 1 , Juliette A. Micone 2 , Jason Tolentino 2 , Sam Keene 3 , Matt Law 1,2 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(E g ) • Promotes “hot” Electron 2. Hot carrier undergoes MEG • MEG is in competition with cooling (emission of phonons) Department of Chemistry 1 , Department of Chemical Engineering and Materials Science 2 , Department of Physics 3 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 MEG 1 • 33% to 44% • 152 nm Exciton Bohr Radius 3 • Best Multiple Exciton Generation (MEG) efficiencies 2 • Labile and oxidizes easily Electrochemical Analogues: 4 • ½ O 2 + 2H + +2e - H 2 O 1.23 V • S + 2H + +2e - H 2 S 0.17 V • Se + 2H + +2e - H 2 Se -0.37 V • Te + 2H + +2e - H 2 Te -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 Al 2 O 3 by atomic layer deposition (ALD). Since the general stability of all sizes of PbTe QDs are very similar in solution, Al 2 O 3 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 nm 3.1 nm 7.1 nm Overall: • PbTe is less stable in air than PbSe Film conditions: • 1494 nm 1 st exciton • Spin Coat 125 nm thick • Soak in 1,2-ethanedithiol • Al 2 O 3 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
