Stability of transparent ZnO front contacts for Cu(In,Ga)Se{sub}2 superstrate solar cells

摘要

The resistivity and the thermal stability of transparent conducting ZnO:Al have been correlated with the conditions of the sputtering process. Layers deposited at low RF power density (～1.3 to 2.6 W/cm{sup}2) exhibit a low resistivity of 9×10{sup}-4 Ωcm, predominantly due to a high concentration of intrinsic donor type defects. These donors are compensated during annealing at high temperature in vacuum; the resistivity increases and the conductivity of the layers are not thermally stable. Depositions at RF power densities of more than 3.2 W/cm{sup}2 yield a high growth rate of 70 nm/min, and the extrinsic Aluminum dopant is incorporated on vacant cation sites. These substitutional donors are thermally stable, and the change in resistivity after annealing at 550°C is below 20%. The influence of Na from the glass substrates has been investigated.