Combinatorial Development of Amorphous Mixed Metal Oxide Transparent Conductors

We are using combinatorial approaches to optimize both amorphous In-Zn-O (a-IZO) and amorphous Zn-Sn-O (a-ZTO) transparent conductors for photovoltaic applications. Compositionally-graded combinatorial samples (``libraries'') are deposited by co-sputtering onto 2"x2" glass substrates at temperatures ranging from room-temperature to 500 \r{ }C. Three to five libraries are generally required to cover the full composition range for a binary tie-line, such as from In2O3 to ZnO. For IZO, we have found that IZO films deposited in Ar at 100 \r{ }C are amorphous for films with 65 to 85 cation{\%} In, with a maximum conductivity of 3000 S/cm at 80 cation{\%} In and an RMS roughness of 0.4 nm. Subsequent sequential annealing experiments in both Ar and air show that a-IZO films are structurally, electrically and optically quite robust for anneals up to 500 or 600 \r{ }C. For a-ZTO, the best conductivity obtained to date for an amorphous ZTO film is 200 S/cm for films grown at 400 \r{ }C with 35 cation{\%} Zn.