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

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

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)

Electrical Conductivity in Ionic Crystals 𝜎 ion = 𝑁 ion 𝑒𝜇 𝜇 ion = 𝐷𝑒 𝑘 𝐵 𝑇 𝐷= 𝐷 0 exp − 𝑄 𝑘 𝐵 𝑇 𝐷 0 = 𝐷 0 𝑐 𝜎 ion = 𝑁 ion 𝐷 0 𝑒 2 𝑘 𝐵 𝑇 exp − 𝑄 𝑘 𝐵 𝑇 𝜎 ion = 𝜎 0 exp − 𝑄 𝑘 𝐵 𝑇 ln 𝜎 ion = ln 𝜎 0 − 𝑄 𝑘 𝐵 𝑇 … electrical conductivity … ion mobility (Einstein’s relationship) … diffusion coefficient … Arrhenius dependence

Electrical Conductivity in Ionic Crystals ln  ln 𝜎 ion = ln 𝜎 0 − 𝑄 𝑘 𝐵 𝑇 Change of activation energy – additional defects in the crystal structure 1/T

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

Application of Amorphous Semiconductors Solar cells Crystalline Efficiency: 18% (in production, single crystals) Landsberg limit: 85,4% Multi-junction solar cells: 41,1% (06.2012) Amorphous Efficiency: 8% Two times cheaper than crystalline semiconductors Electrophotography Laser printer Copier

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