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Semi-conducting organic polymers and Inorganic semiconductor nano-crystals Nir Tessler EE Dept. Technion Semiconducting Organic Polymers The material: Organic semiconductors = molecular materials small molecules to long polymer chains. Soluble Optoelectronic materials (they come as powder or fibers. We dissolve them in the appropriate solvent and cast them from solution. We usually design it such that after drying we get 0.1micron thick solid film) Length scale: Typical layer thickness – 50-100nm Inter chain distance ~ 0.5nm Nano-Materials The original motivation Going from green emission to red emission via simple “block” exchange Chemistry LEGO n + + 1 0.8 0.6 CN 0.4 0.2 CN = CN n 0 400 500 600 700 Wavelength (nm) Organic LEDs one of the best sources for visible light 800 900 The first known application Organic (“plastic”) Displays A proof for the material maturity: Examples from the lab Organic transistor switching organic LED Blue organic LED A “Problem” Polymers emit visible light only! But optical communication elements operate with near infrared light can’t use the low cost “plastic” technology? OK – Lets mix PbSe 5 nm 5nm InAs/ZnSe O Conjugated polymers MeO n Mix It Organic polymer in solution Inorganic semiconductor nano-crystals in solution oc4 oc10 oc4 * n o * OMe n=o=0.5 Mix two solutions to get the right composition Using transmission electron microscope we can also “see” the 5nm crystals in the polymer matrix (i.e. the solid film) After mixing, the plastic polymer do not emit visible light and instead the inorganic nanocrystals emit in the near infrared (telecomm bands) Luminescence (a.u.) Indium Arsenide nanocrystals 1000 Size A Size B 1200 1400 Lead Selenide nanocrystals Size C 1600 Wavelength (nm) 1800 1000 1200 1400 1600 1800 Wavelength (nm) A nice feature – by changing the size of the nanocrystal it is possible to tune the emission to a desired wavelength What happens when you place such a composite film between two electrodes? Ca\Al (cathode) Current/Energy is first O injected into the Polymer polymer - MeO V n Energy/Charge Transfer to the nanocrystal nanocrystal + Light Emission PEDOT/ITO (Anode) Glass The potential Impact The telecomm experts say that for the fiber to the home to happen they need low cost components that can be afforded by any household. Use “plastics” Thanks