1 Electrical Conductivity in Polymers Polymers – van der Waals interactions – bonds of dipole moments Band gap (energy gap) is dependent on interatomic distances

2 Electrical Conductivity in Polymers Changing the band gap via doping causes a change in electrical conductivity

3 Electrical Conductivity in Ionic Crystals Extremely strong bonding forces  large band gap (insulator) Diffusion of positive or negative ions in the crystal lattice (movement of ions, not electrons)

4 Electrical Conductivity in Ionic Crystals … electrical conductivity … mobility of ions (Einstein’s relationship) … diffusion coefficient … Arrhenius dependency

5 Electrical Conductivity in Ionic Crystals 1/T ln  Change of activation energy – additional defects in the crystal structure

6 Electrical Conductivity in Amorphous Materials Interatomic distances in crystalline and amorphous Materials are similar Structure defects acting as voids at doping  new energy states

7 Application of Amorphous Semiconductors Solar cells Crystalline Efficiency: 18% (in production, single crystals) Landsberg limit: 85,4% Multijunction solar cells: 41,1% ( ) Amorphous Efficiency: 8% Two times cheaper than crystalline semiconductors Electrophotography Laser printerCopier

8 Basics of Electrophotography 1.Charging of an amorphous semiconductor (insulator) 2.Exposure – Generation of electron hole pairs via laser radiation – electrical discharge of irradiated area 3.Development – adding toner particles to the charged areas 4.Transfer – transfer of the toner particles from the drum to the paper (in an electric field) 5.Fixing – toner image is permanently fixed to the paper via heat and pressure 6.Cleaning – removal of remaining toner particles from the drum