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  • Research Update: Preserving the photoluminescence efficiency of near infrared emitting nanocrystals when embedded in a polymer matrix Olga Solomeshch and Nir Tessler Citation: APL Mater. 4, 040702 (2016); doi: 10.1063/1.4947570 View online: http://dx.doi.org/10.1063/1.4947570 View Table of Contents: http://scitation.aip.org/content/aip/journal/aplmater/4/4?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Optimization of structural and dielectric properties of CdSe loaded poly(diallyl dimethyl ammonium chloride) polymer in a desired frequency and temperature window J. Appl. Phys. 119, 014108 (2016); 10.1063/1.4939162 Ag +12 ion induced modifications of structural and optical properties of ZnO-PMMA nanocomposite films AIP Conf. Proc. 1512, 394 (2013); 10.1063/1.4791077 Analysis of the forward and reverse bias I-V and C-V characteristics on Al/PVA:n-PbSe polymer nanocomposites Schottky diode J. Appl. Phys. 111, 074513 (2012); 10.1063/1.3698773 Dispersion of Cd X ( X = Se , Te ) nanoparticles in P3HT conjugated polymer J. Renewable Sustainable Energy 1, 023107 (2009); 10.1063/1.3101815 Size-tunable infrared (1000–1600 nm) electroluminescence from PbS quantum-dot nanocrystals in a semiconducting polymer Appl. Phys. Lett. 82, 2895 (2003); 10.1063/1.1570940

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  • APL MATERIALS 4, 040702 (2016)

    Research Update: Preserving the photoluminescence efficiency of near infrared emitting nanocrystals when embedded in a polymer matrix

    Olga Solomeshch and Nir Tessler Microelectronic and Nanoelectronic Centers, Electrical Engineering Department, Technion Israel Institute of Technology, Haifa 32000, Israel

    (Received 25 February 2016; accepted 14 April 2016; published online 21 April 2016)

    Near infrared light emitting nanocrystals are known to lose efficiency when embedded in a polymer matrix. One of the factors leading to reduced efficiency is the labile nature of the ligands that may desorb off the nanocrystal surface when the nanocrystals are in the polymer solution. We show that adding trioctylphos- phine to the nanocrystal-poly(methylmethacrylate) solution prior to film casting enhances the photoluminescence efficiency. The solid films’ photoluminescence quantum efficiency values are reduced by less than a factor of two in the solid form compared to the solution case. We demonstrate record efficiency values of 25% for lead sulfide nanocrystals solid films emitting at 1100 nm. C 2016 Au- thor(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). [http://dx.doi.org/10.1063/1.4947570]

    Nanoscale inorganic materials display unique size, shape, and composition dependent elec- tronic and optical properties. These tunable properties have been implemented in nanocrystal (NC) based devices made of a single component,1,2 as a combination of different nanocrystals or compo- sitions,3 or in hybrid organic-inorganic devices where nanocrystals were interfaced with semicon- ducting polymers.4–10 Despite the progress made in many aspects of nanocrystal’s synthesis and devices made of them, there seems to remain an issue that holds back some applications. There are many reports that although the photoluminescence (PL) efficiency of near infrared (NIR) emitting NCs in solution could be 20% or above, the quantum efficiency (QE) measured for solid films is in the range of 1% and often below it.7 To maintain above 1% efficiency, a higher gap shell is introduced11 and an almost 4%,12 or 12% for low NC loading films,13 is considered very high.

    Our studies of the role of ligands in affecting the energy levels of nanocrystals2,3,10 have empha- sized the role of ligand exchange which is based on the fact that most ligands would dynamically detach and reattach to the nanocrystal’s surface. This has led us to postulate that diluting the nanocrystals in a matrix also dilutes the ligands and thus favors the situation where part of the nanocrystal’s surface becomes non-passivated thus dropping the PL efficiency. Ligand desorption in dilute solutions and the role of surface coverage in affecting the emission quantum yield have been reported in Refs. 14–16. Here we report that adding excess ligands to the solution of, commer- cially available, lead sulfide PbS nanocrystal results is in PL efficiency, of NCs embedded in a poly(methylmethacrylate) (PMMA) matrix, of 25% and 12% for nanocrystals emitting at 1100 nm and 1500 nm, respectively.

    For this study, we purchased two types of commercially available colloidal lead sulfide (PbS) nanocrystals (NCs) series C (SCR) from CAN GmbH (www.can-hamburg.com) as solutions in toluene. The NCs size distribution was slightly improved through size selection procedures carried out by the manufacturer. A polymer host, poly(methylmethacrylate) PMMA solution in toluene, and additives of trioctylphosphine (TOP) and/or aniline, both purchased from Aldrich, were used to prepare free standing films from polymer-NCs blends. The use of relatively thick films was to ensure sufficient absorption in the NIR to ensure accurate efficiency measurements (see method below).

    2166-532X/2016/4(4)/040702/5 4, 040702-1 ©Author(s) 2016.

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