Physics of Organic Semiconductor Devices: Materials, Fundamentals, Technologies and Applications Dr. Alex Zakhidov Assistant Professor, Physics Department Core faculty at Materials Science, Engineering and Commercialization Program. http://zakhidov.wp.txstate.edu/ Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Outline 1. Why organic electronics and what is it good for? 2. How to save the world with organic perovskite solar cells? Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Organic Electronics Devices: Smart, Flexible, Cheap! Organic Light Organic Solar Cell Organic Thin Film Emitting Diode (OLED) (OSC) Transistor (OTFT) Samsung Heliatek Other devices: organic lasers, organic memory, organic bio(chemical) sensors Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov “Evolution” of organic electronics New material synthesis: design, polymers, small molecules progress Chemistry Structure, film morphology morphology film Structure, Mobility, optical optical properties, Mobility, Materials properties: Materials OLEDs Materials Materials Used for mobile Science Science displays and TVs (2012) Physics Physics Commercial prototypes (2000s) Fundamentals, mechanism of mechanism Fundamentals, operation, new device new concepts device operation, First devices (late 1980s) Engineering Materials (1960-70) Enabling technologies: Processing, patterning, doping, encapsulation Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Organic compounds contain carbon S.R. Forrest ,Nature 428 (2004) Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Organic Semiconductors – π - conjugated organic molecules linear aromatic Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Organic Semiconductors – π - conjugated organic molecules In 1977, they discovered that polyacetylene can be oxidized with halogensto produce conducting materials from either insulating or semiconducting materials. + I Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov General Features of Organic Semiconductors Advantages Challenges 1. Device engineering. (Lithography, 1. Unlimited material design options Doping, Materials purity, Horizontal and 2. Varity of structures and morphologies vertical integration) 3. Band gap engineering 2. Stability, Lifetime 4. Light, flexible, inexpensive 3. Organic/Inorganic Interfaces 5. Electronic and Ionic transport* 4. Disorder: highly localized charge carriers 6. Disorder: highly localized exciton amorphous lamella nano-crystalline microcrystalline crystalline L 1 nm 10nm 100nm 1µm 10 µm 100 µm 1 mm *Al.A. Zakhidov, B. Jung, J.D. Slinker, H.D. Abruña, G.G. Malliaras, “A light-emitting memristor”, Organic Electronics 11, 150 (2010). Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Electronic properties of Organic Semiconductors Graphene p-Si GaAs, Organic semiconductors CMOS InSb, GaN, Organic semiconductors InAs a-Si Mobility cm2/Vs 10-6 10-5 10-4 10-3 10-2 10-1 1 10 102 103 104 105 Amorphous Highly crystalline T. Sekitani, et. al. Nature Materials 9 (2010) H. Klauk, Chemical Society Reviews, 39 (2010 ) Google *Y. Yuan, et al Nature Communications 5 (2013). Lens to monitor glucose level in tear Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Optical properties of Organic Semiconductors Organics: Frenkel excitons Inorganics: Wannier-Mott excitons εorg<< εinorg 2 Eex=e /(ε·rex) Molecular picture Semiconductor picture kbTroom~26 meV Ground State Frenkel exciton Ground State WM exciton Binding energy ~ 1 eV Binding energy ~ 10 meV Radius ~ 10 Å Radius ~ 100 Å Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Happy Life… Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov How much do we need? Eco Friendly In fact can help us to “deal” with global climate change Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Why are we not doing this already? Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov National Renewable Energy Lab Solar chart $$ 20% $$$$ $, but…. $$$ Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Perovskite structure and processing Organic Inorganic Spin/dip-coating CH3NH3 precursor precursor Pb X CH3NH3I + PbX2 Vacuum co-deposition Where X - Br, I or Cl. Generic perovskite solar cell Perovskite layer top view Ag Hole Selective layer perovskite absorber Electron Selective layer ITO/FTO Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Organic Perovskite Solar Cells Advantages Challenges 1. Stability 1. Efficiency >20% 2. High optical absorption 2. Replacement of lead with tin 3. Low recombination rates 4. High carrier transport mobility 3. Reliable, scaled-up production 5. Tunable band gap 6. Room temperature processing 7. Low-cost, abundant materials The Energy Pay Back Time EPBT = Einput/Esaved organic solar cells Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov Take home message Physics Colloquium 10/07/2015 , Dr. Alex Zakhidov.