Hybridized electronic states between CdSe nanoparticles and conjugated organic ligands: A theoretical and ultrafast photo-excited carrier dynamics study
Formation of densely packed thin films of semiconductor nanocrystals is advantageous for the exploitation of their unique optoelectronic properties for real-world applications. Here we investigate the fundamental role of the structure of the bridging ligand on the optoelectronic properties of the resulting hybrid film. In particular, we considered hybrid films formed using the same CdSe nanocrystals and two organic ligands that have the same bidentate dithiocarbamate binding moiety, but differ in their bridging structures, one bridged by ethylene, the other by phenylene that exhibits conjugation. Based on the results of photo-excited carrier dynamics experiments combined with theoretical calculations on the electronic states of bridged CdSe layers, we show that only the phenylene-based ligand presents a strong hybridization of the molecular HOMO state with CdSe layers, that is a marker of formation of an effective bridge. We argue that this hybridization spread favors the hopping of photo-excited carriers between nanocrystals, which may explain the reported larger photo-currents in phenylene-based hybrid films than those observed in ethylene-based ones.
Keywordshybrid layer-by-layer film ultrafast spectroscopy CdSe nanoparticles molecular orbitals density functional theory
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- Nguyen Truong, N. T.; Ngoc Nguyen, T. P.; Park, C. Structural and optoelectronic properties of CdSetetrapod nanocrystals for bulk heterojunction solar cell applications. Int. J. Photoenergy 2013, 2013, Article ID 146582.Google Scholar
- Virgili, T.; Calzolari, A.; Suárez López, I.; Vercelli, B.; Zotti, G.; Catellani, A.; Ruini, A.; Tassone, F. Charge separation in the hybrid CdSenanocrystal–organic interface: Role of the ligands studied by ultrafast spectroscopy and density functional theory. J. Phys. Chem. C 2013, 117, 5969–5974.CrossRefGoogle Scholar
- Constantine, C. A.; Gattás-Asfura, K. M.; Mello, S. V.; Crespo, G.; Rastogi, V.; Cheng, T. C.; DeFrank, J. J.; Leblanc, R. M. Layer-by-layer films of chitosan, organophosphorus hydrolase and thioglycolic acid-capped CdSe quantum dots for the detection of paraoxon. J. Phys. Chem. B 2003, 107, 13762–13764.CrossRefGoogle Scholar
- Zotti, G.; Vercelli, B.; Berlin, A.; Chin, P. T. K.; Giovanella, U. Self-assembled structures of semiconductor nanocrystals and polymers for photovoltaics. 1. CdSenanocrystal-polymer multilayers. Optical, electrochemical, photoelectrochemical and photoconductive properties. Chem. Mater. 2009, 21, 2258–2271.Google Scholar
- Zotti, G.; Vercelli, B.; Berlin, A.; Pasini, M.; Nelson, T. L.; McCullough, R. D.; Virgili, T. Self-assembled structures of semiconductor nanocrystals and polymers for photovoltaics. 2. Multilayers of CdSe nanocrystals and oligo(poly)thiophenebased molecules. Optical, electrochemical, photoelectrochemical, and photoconductive properties. Chem. Mater. 2010, 22, 1521–1532.Google Scholar
- Giannozzi, P.; Baroni, S.; Bonini, N.; Calandra, M.; Car, R.; Cavazzoni, C.; Ceresoli, D.; Chiarotti, G. L.; Cococcioni, M.; Dabo, I. et al. QUANTUM ESPRESSO: Amodular and open-source software project for quantum simulations of materials. J. Phys.: Condens. Matter 2009, 21, 395502.Google Scholar