Article pubs.acs.org/JPCC
Investigation of the Photophysical and Electrical Characteristics of CuInS2 QDs/SWCNT Hybrid Nanostructure Razi Ahmad,†,‡ Udit Soni,‡ Ritu Srivastava,*,† Vidya Nand Singh,§ Suresh Chand,† and Sameer Sapra‡ †
Center for Organic Electronics, Physics of Energy Harvesting Division, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India ‡ Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India § Electron and Ion Microscopy Section, CSIR-National Physical Laboratory, Dr. K. S. Krishnan Road, New Delhi 110012, India ABSTRACT: A novel photoactive hybrid nanostructure based on zero-dimensional (0-D) light-harvesting components of CuInS2 quantum dots (QDs) and one-dimensional (1-D) transporting channel of single-wall carbon nanotube (SWCNT) was synthesized by hydrophobic interaction between alkyl chain of dodecanethiol molecule (QDs surface) and octadecylamine (CNT surface). Photophysical and electrical characterizations suggest that an efficient electron transfer from photoexcited CIS QDs to SWCNT takes place. Furthermore, size-dependent optical study shows that faster electron transfer takes place from CIS to SWCNT for small-size QDs compared to large-size quantum dots. The rate constant for electron transfer from photoexcited CIS to SWCNT increased from 1.9 × 106 to 3.5 × 106 s−1 with decrease in the size of CIS QDs from 5.0 to 3.5 nm.
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many future applications such as nanoelectronics,15 solar cells,16 transistor,17 and photodetectors.18,19 The unique properties of CNTs such as large surface area, high aspect ratio, 1-D structure, and high electron mobility provide direct charge carrier transport path to electrodes. In order to improve the charge separation and electron transport, semiconductor QDs/ CNT and QDs/GO hybrid nanostructures are widely investigated. The hybrid nanostructure based on QDs decorated CNT and GO emerges as a new class of material suitable for efficient optoelectronic devices and photocatalysis.20−24 These hybrid nanomaterials possess the unique properties of both the materials. It has been reported that the hybrid nanostructure mixed with conjugated polymers enhances the performance of optoelectronic devices such as photodetector25,26 and solar cells.27−30 In this work, we report the synthesis of a novel photoactive hybrid nanostructure: CIS decorated single-walled carbon nanotube. The QDs are anchored on the surface of SWCNT by hydrophobic interaction between alkyl chain of dodecanethiol (DDT) and octadecylamine (ODA). Size-dependent electron transfer from photoexcited CIS to SWCNT has been investigated by using steady-state and time-resolved fluorescence spectroscopy. The electrical characteristics of the hybrids were studied by combining them with a hole-transporting
INTRODUCTION Colloidal semiconductor nanocrystals (NCs) or quantum dots (QDs) have been widely investigated zero-dimensional (0-D) nanomaterials for possible application in solution-processed optoelectronic devices due to their shape- and size-dependent optical properties.1−6 The unique properties of quantum dots such as high optical absorption cross section, a wider absorption range tunable from visible to NIR achievable by varying particle size, and high carrier mobility make it an ideal candidate for light-harvesting component in photovoltaic devices. The widely used quantum dots such as cadmium or lead-based chalcogenides have shown great potential in photovoltaic devices.7−10 However, due to the toxic nature of Cd and Pb, these QDs have a doubtful future. The ternary nontoxic and environment friendly CuInS2 (CIS) quantum dots have a great potential as the lightharvesting component in solution-processed photovoltaic devices. Furthermore, CIS QDs exhibit high optical absorption coefficient (105 cm−1 in the visible range) and narrow band gap which is well matched with the optimal spectral range for photovoltaic devices.11 Despite the above-mentioned advantages, the use of CIS QDs in optoelectronic applications has been limited by poor transport properties arising due to insulating ligands, interparticle hops, and absence of interconnected percolation network for charge transport.12−14 Single-wall carbon nanotube (SWCNT) is one of the most fascinating one-dimensional nanostructured material from the family of carbon-based nanomaterials. The size- and structuredependent electronic properties make it an ideal candidate in © 2014 American Chemical Society
Received: November 25, 2013 Revised: May 1, 2014 Published: May 1, 2014 11409
dx.doi.org/10.1021/jp411568c | J. Phys. Chem. C 2014, 118, 11409−11416
The Journal of Physical Chemistry C
Article
FEI Tecnai G2 F30 STWIN) operating at an accelerating voltage of 300 kV. Absorption and steady-state fluorescence spectroscopy were carried out using a UV−vis spectrophotometer (Shimadzu 2401 PC) and Fluorolog (Jobin YvonHoriba, model 3-11) spectroflouorometer, respectively. PL emission lifetime decays were collected using time-correlated single photon counting (TCSPC) using Fluorolog (Jobin YvonHoriba, model 3-11) spectroflouorometer. A pulsed Nano-LED (405 nm) with pulse width
