Direct current sputtered aluminum-doped zinc oxide films for thin crystalline silicon heterojunction solar cell

The high-power high-throughput direct current (DC) magnetron sputtering of aluminum-doped zinc oxide (AZO) film was investigated for fabricating amorphous silicon/crystalline silicon heterojunction solar cells. The AZO films were deposited using 1.0 wt.% and 2.0 wt.% Al-doped ZnO targets. The functional properties of the deposited films were characterized by measuring the electrical conductivity, Hall mobility, free carrier density and optical transparency. The influence of the sputtering power, oxygen concentration, substrate temperature, post-annealing and film thickness on the film properties were studied systematically. The oxygen in the sputtering gas deteriorates the electrical and optical performance of AZO films, which can be improved by post annealing. An optimal value of 1.0 × 10−3 Ω cm for the resistivity and 90% for the optical transmission was obtained at processing temperatures below 250 °C. Two types of thin Si heterojunction solar cells were prepared and compared using DC sputtered AZO film as the front electrode. Results show that DC sputtered AZO films meet the requirements for use as transparent front electrode in thin Si heterojunction solar cells.