CH. 3 Solar Cell Basic III: Principle Organic Materials for Electronics and Photonics II

2 Light Emitting Diodes Electric energy to light energy Materials for LED Light Electric energy LED

3 Mechanism of p-n Junction C. B. V. B. EFEF C. B. V. B. EFEF Energy

4 Mechanism of p-n Junction Depletion Layer Energy

5 Mechanism of p-n Junction + - h Energy Forward bias

6 PLED LED Inorganic Organic (OLED) Small Molecules (SMOLED) Polymer (PLED) PLED (Polymer Light Emitting Diode) - LED used polymer not only as the semiconductor material in LEDs but also as the composition of LED (substrate, active layer, electrode, etc.). Advantages of PLED - low cost - low operating voltage - fast response time - full color emission - large area, flat, flexible display - easy fabrication

7 Structure of PLED ITO Sputtering ITO Patterning - Photolithography ITO glass cleaning HTL coating (PEDOT:PSS) - Spin coating Emitting layer coating - Spin coating Aluminum evaporation

8 Aluminum polymer ITO Glass Mechanism of PLED h Anode cathode Polymer + -

Evolution of Display CRTLCDPDP Organic EL Flexible display

10 Requirement for Flexible Display Substrate ⇒ Flexible !! (Glass → Plastic) Emitting layer ⇒ Flexible Semiconducting polymer Electrode ⇒ Flexible electrode Flexible packaging material

11 ITO as Flexible Electrode Require a ‘genuine’ flexible & transparent electrode!!

12 Requirements for Flexible Electrode 1. Flexibility 2. Conductivity 3. Transparency Plastic Electrode using Conducting Polymer

13 Molecular Scale Disorder Reduction of K. Lee & S.H. Lee Nature 441 (2006) 65. σ dc ≥ 1,000 S/cm “Recent Invention of New Metallic Polyaniline”

14 Metallic PANI Electrode Molecular Scale Disorder Reduction of K. Lee et al. Nature 441 (2006) 65. σ dc ≥ 1,000 S/cm

15 PANI Electrode : Flexible LED

16 Flexible Electrode using Metallic PANI Flexible Solar Cell Flexible LED New PANI Electrode