Novel coatings for solar cells with the capability of controlled charge storage

Functional coatings for solar cells, namely thermally grown SiO ₂, cold plasma deposited SiO₂ and amorphous Teflon AF, are introduced as passivation layers as well as materials for electric charge storage. These so called electrets, originally investigated for electret-condenser microphones, have been applied to MIS-solar cells. Layer preparation, controlled corona charging, and thermal and optical charge storage characteristics are described. These electret films are stable for several years and resists photons with energies of less than 3.0 eV and at least 5 eV for positively or negatively charged films, respectively. On solar cell test structures it is shown, that the I-V characteristic is drastically influenced by electret charge polarity and density. Numerical simulations revealed the potential of this concept