Grain boundary effects and conduction mechanism studies in chromium metal-insulator-silicon solar cells on polycrystalline silicon

Chromium metal-insulator-silicon (MIS) solar cells fabricated on Wacker polycrystalline silicon and electron-beam-deposited thin film silicon were studied to determine current flow mechanisms. Wacker polycrystalline p-type silicon was shown to produce MIS solar cells which exhibit surface-state-controlled current for T>150 K and tunneling-controlled current at lower temperatures. MIS cells on unpolished Wacker silicon are clearly space charge limited. Electron-beam-deposited polycrystalline silicon 20 - 30 μm thick has a conductivity which may be limited by the grain boundary trap density or the availability of free carriers. Surface state analysis, laser scan data and diffusion length studies also show the limitations which exist at grain boundaries of polycrystalline silicon.