{"id":2134,"date":"2010-07-14T15:54:56","date_gmt":"2010-07-14T19:54:56","guid":{"rendered":"https:\/\/wpmu2.mit.local\/?p=2134"},"modified":"2010-07-15T12:30:48","modified_gmt":"2010-07-15T16:30:48","slug":"2134","status":"publish","type":"post","link":"https:\/\/wpmu2.mit.local\/2134\/","title":{"rendered":"High-efficiency Infrared Colloidal Quantum-dot Light-emitting Diodes"},"content":{"rendered":"
\"Figure<\/a>

Figure 1: Normalized infrared electroluminescence (black, solid) and photoluminescence (red, crosses) spectra of a PbS QD-LED centered at 1.11 \u00b5m. The inset shows the general device structure.<\/p><\/div>\n

\"Figure<\/a>

Figure 2: Tapping-mode Atomic Force Microscope (AFM) phase image of nearly complete monolayer coverage of an organic HTL by ~4 nm PbS QDs. QDs have the tendency to pack into regular hexagonal arrays. The inset illustrates a two-dimensional spatial Fourier Transform of the area delineated by the dashed box, revealing the expected six-point pattern.<\/p><\/div>\n

While boasting high performances and long lifetimes, the associated fabrication and materials costs of established infrared (IR) technologies (such as inorganic light-emitting diodes (LEDs) and lasers) preclude their use in cost-constrained, large-area applications [1<\/a>]<\/sup>. Solution-processable LEDs promise lower manufacturing costs and compatibility with a variety of (flexible) substrates. In the IR <\/ins>region, the incorporation of solution-processable IR light-emitters into on-chip optoelectronic integrated circuits is an alluring possibility [1<\/a>]<\/sup>. Optical diagnosis in biologically transparent windows at 800, 1100, and 1300 nm could also be performed using large-area IR emitters [2<\/a>]<\/sup>. However, solution-processable molecular and polymeric organic LEDs have limited extendibility into the IR region owing to negligible optical activity beyond 1 \u00b5m [1<\/a>]<\/sup>. In contrast, colloidal quantum-dot LEDs (QD-LEDs) combine the thin <\/ins>film processability of organic materials with the tunable optical properties conferred by QD size control. Additionally, the colloidal PbS QDs employed here can be reproducibly synthesized with a narrow size distribution, demonstrate greater stability [3<\/a>]<\/sup> than PbSe (on which several previously reported devices have been based [1<\/a>]<\/sup>), and exhibit a remarkably high thin-film absolute photoluminescence (PL) efficiency of 18 to 20 %.<\/p>\n

We report efficient IR electroluminescence (EL) from large-area (mm2<\/sup> in size) LEDs comprising solution-deposited colloidal PbS QDs sandwiched between organic hole- and electron-transporting layers (HTL\/ETL) deposited at room temperature, as shown in the inset of Figure 1. Spin-casting of a blend solution of QDs and a hole transporting material yields a QD monolayer at the surface via a spontaneous phase-segregation process previously reported by our group [4<\/a>]<\/sup> (see Figure 2). IR EL is observed at turn-on voltages as low as 4 V and closely resembles the corresponding QD PL spectrum (Figure 1).<\/p>\n

\r\nReferences
  1. J. S. Steckel, S. Coe-Sullivan, V. Bulovi\u0107 and M. G. Bawendi, \u201c1.3 \u00b5m to 1.5 \u00b5m Tunable Electroluminescence from PbSe Quantum Dots Embedded within an Organic Device,\u201d Advanced Materials<\/em>, vol. 15, no. 21, pp. 1862-1866, November 2003. [↩<\/a>] [↩<\/a>] [↩<\/a>] [↩<\/a>]<\/li>
  2. G. Konstantatos, C. Huang, L. Levina, Z. Lu and E. H. Sargent, \u201cEfficient Infrared Electroluminescent Devices Using Solution-Processed Colloidal Quantum Dots,\u201d Advanced Functional Materials<\/em>, vol. 15, pp. 1865-1869, September 2005. [↩<\/a>]<\/li>
  3. J. Tang, X. Wang, L. Brzozowski, D. A. R. Barkhouse, R. Debnath, L. Levina and E. H. Sargent, \u201cSchottky Quantum Dot Solar Cells Stable in Air under Solar Illumination,\u201d Advanced Materials<\/em>, vol. 22, pp. 1398-1402, January 2010. [↩<\/a>]<\/li>
  4. S. Coe-Sullivan, J. S. Steckel, W-K. Woo, M. G. Bawendi, V.\u00a0 Bulovi\u0107, \u201cLarge-Area Ordered Quantum-Dot Monolayers via Phase Separation During Spin-Casting,\u201d Advanced Functional Materials<\/em>, vol. 15, pp. 1117-1124, April 2005. [↩<\/a>]<\/li><\/ol><\/div>","protected":false},"excerpt":{"rendered":"

    While boasting high performances and long lifetimes, the associated fabrication and materials costs of established infrared (IR) technologies (such as…<\/p>\n<\/div>","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[12],"tags":[4232,46],"_links":{"self":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/2134"}],"collection":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/comments?post=2134"}],"version-history":[{"count":8,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/2134\/revisions"}],"predecessor-version":[{"id":2179,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/posts\/2134\/revisions\/2179"}],"wp:attachment":[{"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/media?parent=2134"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/categories?post=2134"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wpmu2.mit.local\/wp-json\/wp\/v2\/tags?post=2134"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}