Optical absorption and electrical conductivity in amorphous In-Zn-O: A new TCO for CIGS PV

We report the coupled optical and electrical properties of a-IZO films as a function of both the metals composition and the %O₂ in the Ar/O₂ sputter gas mix. In particular, a-IZO films with conductivity ¿ > 2000 S/cm can be grown for a broad range of metals compositions (60 to 85 at.% In) as long as the corresponding optimal oxygen level is used in the deposition. The amount of oxygen required increases with increasing indium content. When too much oxygen is used, the a-IZO remains clear but the conductivity is reduced due to a decreased carrier concentration. Whereas, when too little oxygen is used, the conductivity is reduced due to decreased electron mobility and there is a concurrent increase in the optical absorption from 400 to 1000 nm which renders the oxygen deficient a-IZO samples gray.