Adsorption and Electron Injection for CdSe on TiO2

Tracking the Adsorp2on and Electron Injec2on Rates of CdSe Quantum Dots on TiO2: Linked versus Direct ADachment Douglas R. Pernik, Kevin Tvrdy, James G. Radich, Prashant V. Kamat J. Phys. Chem. C, 2011, 115 (27), pp 13511-‐13519 Department of Chemical and Biomolecular Engineering Department of Chemistry and Biochemistry RadiaHon Laboratory, University of Notre Dame

Big Picture •  Quantum dot sensiHzed solar cells (QDSSCs) are cheap devices for converHng solar energy to electricity •  Current QDSSCs lack in eﬃciency compared to crystalline silicon •  Improvements are needed at the QDSSC working electrode Goals of this work: – Understand quantum dot adsorpHon phenomenon on TiO2 – Examine charge carrier dynamics for QD-‐TiO2 assemblies

Goal 1: Understand QD AdsorpHon Phenomenon on TiO2 Experimental setup for monitoring CdSe QD adsorpHon on TiO2. AdsorpHon is seen over Hme with UV-‐Visible absorpHon spectrometry.

AdsorpHon Processes QDs begin to form a monolayer on TiO2 before aggregaHng on the TiO2 surface

AdsorpHon Modeling 0.06 Experimental Adsorption Data Sub-Monolayer Adsorption QD AggregationFractional Coverage of TiO2 0.05 Total Fit 0.04 0.03 0.02 0.01 0.00 0 10 20 30 40 50 Time (Hours) AdsorpHon is seen as a combinaHon of monolayer formaHon and QD aggregaHon on TiO2

Eﬀect of Washing on QD AdsorpHon 25 QD Adsorbed Per TiO2 Nanoparticle 5 Washes 20 15 3 Washes 10 5 1 Wash 0 0 10 20 30 40 50 Time (Hours) Methanol pretreatment (washing) improves QD aﬃnity for TiO2

Goal 2: Examine Charge Carrier Dynamics for QD-‐TiO2 Assemblies Flow of Electrons Electron Electrolyte Light Transfer QD TiO2 Photoanode Photocathode How does the presence of a molecular linker aﬀect electron injecHon rates?

Electron InjecHon Rates "#$%&!($)* +,- +,. +,/ 0,1 !D! (3D3I* !"#$%&()$"%*+%#,-./,-<=>, ∆<=>,?/,0 0 !"#$%&()*+,-),./01$)$ !D! (=D=I* !"#$%"0$1*&2%3**314$"%*+%#,-./,- 5$67+($(*3&%5$8*9:* ! !!!!!!!!!!! |∆<=>@%=3#A$B!(#@%8,!83C?0* ()9 ∆<?/,//+ (89 3 #-234!"#$%&()*+ = ! 3I ()9∆<=>@%=3#A$ ∆<?/,//+ (89 .-234!"#$%&()*+ =I ()9 ∆<?/,//+ (89 #-23456#4!"#$%&()*+ ! ()9 ∆<?/,//- (89 .-2345674!"#$%&()*+ / 9-/ -// --/ :// :-/ ;// / +/ 9/ :/ 1/ 0// 234$5$#&67!(#8* E$53!FG8$!(H>* Electron injecHon is more rapid when QDs are directly adsorbed onto TiO2. The linker molecule 3-‐MPA acts as a physical barrier to charge transfer

Summary •  Development of a method to monitor and model QD adsorpHon onto TiO2 over Hme •  Importance of QD washing to achieve high coverage of TiO2 •  AdsorpHon is seen as a combinaHon of monolayer formaHon and parHcle aggregaHon •  Linker molecules have a detrimental effect on electron injecHon rates These findings will aid in construcHng quantum dot sensiHzed solar cells with higher efficiency

Special Thanks – U.S. Department of Energy for project funding – Vincent P. Slac Fellowship for Undergraduate Research, provided by Notre Dame Energy Center This work is published in the Journal of Physical Chemistry C: J. Phys. Chem. C, 2011, 115 (27), pp 13511-‐13519 DOI: 10.1021/jp203055d AddiHonal informaHon about the Kamat group is on the group website: hcp://nd.edu/~pkamat/

Adsorption and Electron Injection for CdSe on TiO2

by kamatlab on Sep 12, 2011

Accessibility

Categories

Tags

Upload Details

Usage Rights

Statistics

Adsorption and Electron Injection for CdSe on TiO2 — Webinar Transcript