Controlled fabrication of pbs quantum-dot/carbon-nanotube nanoarchitecture and its significant contribution to near-infrared photon-to-current conversion

Abstract

A solution-processed nanoarchitecture based on PbS quantum dots (QDs) and multi-walled carbon nanotubes (MWCNTs) is synthesized by simply mixing the pre-synthesized high-quality PbS QDs and oleylamine (OLA) pre-functionalized MWCNTs. Pre-functionalization of MWCNTs with OLA is crucial for the attachment of PbS QDs and the coverage of QDs on the surface of MWCNTs can be tuned by varying the ratio of PbS QDs to MWCNTs. The apparent photoluminescence (steady-state emission and fluorescence lifetime) "quenching" effect indicates efficient charge transfer from photo-excited PbS QDs to MWCNTs. The as-synthesized PbS-QD/MWCNT nanoarchitecture is further incorporated into a hole-conducting polymer poly(3-hexylthiophene)- (P3HT), forming the P3HT:PbS-QD/MWCNT nanohybrid, in which the PbS QDs act as a light harvester for absorbing irradiation over a wide wavelength rangeof the solar spectrum up to near infrared (NIR,.1430 nm) range; whereas, the one-dimensional MWCNTs and P3HT are used to collect and transport photoexcited electrons and holes to the cathode and anode, respectively. Even without performing the often required "ligand exchange" to remove the long-chained OLA ligands, the built nanohybrid photovoltaic (PV) device exhibits a largely enhanced power conversion efficiency (PCE) of 3.03% as compared to 2.57% for the standard bulk hetero-junction PV cell made with P3HT and [6,6]-Phenyl-C61 -Butyric Acid Methyl Ester (PCBM) mixtures. The improved performance of P3HT:PbS-QD/MWCNT nanohybrid PV device is attributed to the significantly extended absorption up to NIR by PbS QDs as well as the effectively enhanced charge separation and transportation due to the integrated MWCNTs and P3HT. Our research results suggest that properly integrating QDs, MWCNTs, and polymers into nanohybrid structures is a promising approach for the development of highly efficient PV devices. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.