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
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

5. 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

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%
Multi-junction solar cells: 41,1%
( )
Amorphous
Efficiency: 8%
Two times cheaper than crystalline semiconductors
Electrophotography
Laser printer
Copier

8. 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