Controlling photoinduced electron transfer from PbS@CdS core@shell quantum dots to metal oxide nanostructured thin films

Year: 2014

Authors: Zhao H., Fan Z., Liang H., Selopal GS., Gonfa BA., Jin L., Soudi A., Cui D., Enrichi F., Natile MM., Concina I., Ma D., Govorov AO., Rosei F., Vomiero A.

Autors Affiliation: CNR INO SENSOR Lab, I-25123 Brescia, Italy; Inst Natl Rech Sci, Varennes, PQ J3X 1S2, Canada; Ohio Univ, Dept Phys & Astron, Athens, OH 45701 USA; Univ Brescia, SENSOR Lab, Dept Informat Engn, I-25133 Brescia, Italy; Lab Nanofab Veneto Nanotech, I-30175 Marghera, Italy; CNR IENI, I-35131 Padua, Italy; Univ Padua, Dept Chem Sci, I-35131 Padua, Italy; McGill Univ, Ctr Self Assembled Chem Struct, Montreal, PQ H3A 2K6, Canada.

Abstract: N-type metal oxide solar cells sensitized by infrared absorbing PbS quantum dots (QDs) represent a promising alternative to traditional photovoltaic devices. However, colloidal PbS QDs capped with pure organic ligand shells suffer from surface oxidation that affects the long term stability of the cells. Application of a passivating CdS shell guarantees the increased long term stability of PbS QDs, but can negatively affect photoinduced charge transfer from the QD to the oxide and the resulting photoconversion efficiency (PCE). For this reason, the characterization of electron injection rates in these systems is very important, yet has never been reported. Here we investigate the photoelectron transfer rate from PbS@CdS core@shell QDs to wide bandgap semiconducting mesoporous films using photoluminescence (PL) lifetime spectroscopy. The different electron affinity of the oxides (SiO2, TiO2 and SnO2), the core size and the shell thickness allow us to fine tune the electron injection rate by determining the width and height of the energy barrier for tunneling from the core to the oxide. Theoretical modeling using the semi-classical approximation provides an estimate for the escape time of an electron from the QD 1S state, in good agreement with experiments. The results demonstrate the possibility of obtaining fast charge injection in near infrared (NIR) QDs stabilized by an external shell (injection rates in the range of 110-250 ns for TiO2 films and in the range of 100-170 ns for SnO2 films for PbS cores with diameters in the 3-4.2 nm range and shell thickness around 0.3 nm), with the aim of providing viable solutions to the stability issues typical of NIR QDs capped with pure organic ligand shells.

Journal/Review: NANOSCALE

Volume: 6 (12)      Pages from: 7004  to: 7011

More Information: A.V. acknowledges the European Commission for partial funding under the contract F-Light Marie Curie no. 299490. The authors acknowledge the European Commission for partial funding under the contract WIROX no. 295216. I. C. acknowledges Regione Lombardia under X-Nano Project (Emettitori di elettroni a base di nano tubi di carbonio e nano strutture di ossidi metallici quasi monodimensionale per lo sviluppo di sorgenti a raggi X) for partial funding. G. S. S. acknowledges OIKOS s.r.l. for funding. M.M.N. acknowledges the Italian MIUR under the project FIRB RBAP114AMK RINAME for partial funding. H. L. acknowledges FRQNT for a PhD scholarship. F. R. acknowledges the Canada Research Chairs program for partial salary support. F. R. is grateful to the Alexander von Humboldt Foundation for a F. W. Bessel Award. F. R. and D. M. acknowledge NSERC for funding from Discovery, Equipe and Strategic grants and MDEIE for partial funding through the project WIROX. F. R. is supported by Elsevier through a grant from Applied Surface Science and H.Z. acknowledges funding from NSERC through PDF fellowship. I. C. and A. V. acknowledge Regione Lombardia for partial funding under the project Tecnologie e materiali per l’utilizzo efficiente dell’energia solare.
KeyWords: Solar-cells; Charge-transfer; Tio2; Nanocrystals; Heterojunctions; Photovoltaics; Nanoparticles; Injection; Emission
DOI: 10.1039/c4nr01562b

Citations: 75
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