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