Quantum Dot Surface Chemistry: Ligand Effects and Electron Transfer Reactions

• Published in: Journal of physical chemistry. C Vol. 117; no. 27; pp. 14418 - 14426
• Main Authors: Hines, Douglas A, Kamat, Prashant V
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 11.07.2013
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Electronics; Energy; Exact sciences and technology; Materials science; Molecular electronics, nanoelectronics; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Natural energy; Photovoltaic conversion; Physics; Quantum dots; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Solar cells. Photoelectrochemical cells; Solar energy; Encapsulation; Amines; Quantum chemistry; Surface chemistry; Fluorescence; Electron transfer; Surface treatments; Transients; Thin films; Surface effect; Traps; Absorption band; Alanines; Absorption spectra; Solar cells; Quantum dots; Excited states; Quantum yield; Steady state; III-V compound; Interfaces; Electronic structure; Excitons; Electron state; Ligands; Nanostructured materials
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp404031s

With the increased interest in quantum dot sensitized solar cells (QDSCs) there comes a need to better understand how surface modification of quantum dots (QDs) can affect the excited state dynamics of QDs, electron transfer at the QD–metal oxide (MO) interface, and overall photoconversion efficiency of QDSCs. We have monitored the surface modification of solution based QDs via the steady state absorption and emission characteristics of colloidal CdSe passivated with β-alanine (β-Ala). The trap-remediating nature of the β-Ala molecule, arising from the Lewis basicity of the amine group, is realized from the hypsochromic shifts seen in excitonic absorption and emission bands as well as an increase in fluorescence quantum yield. Transient absorption measurements of CdSe–TiO2 films prepared with and without β-Ala as a linker molecule further reveal the role of the surface modifier in influencing excited state electron transfer processes. Electron transfer at this interface was found to be dependent on the method of QD deposition: CdSe–TiO2 (direct deposition, k et = 1.5 × 1010 s–1), CdSe–linker–TiO2 (attaching linker molecule first to TiO2 so that β-Ala interaction is minimal, k et = 2.4 × 109 s–1), or linker–CdSe–linker–TiO2 (linkage via full β-Ala encapsulation in solution prior to deposition, k et = 6.4 × 108 s–1). These results imply that the surface chemistry of colloidal CdSe plays an important role in mediating electron transfer reactions.