EFFECT OF OXYGEN DURING THERMAL ANNEALING ON THE ELECTRICAL AND OPTICAL PROPERTIES OF SPUTTER DEPOSITED AL-DOPED ZNO FILMS FOR HETEROJUNCTION SOLAR CELL APPLICATION

摘要

The influence of oxygen during short post deposition annealing on Al-doped zinc oxide (AZO) films for heterojunction solar cells grown by sputter deposition is investigated in terms of their electrical, optical and structural properties. AZO films were annealed for 4 min at 300°C and 450°C in ambient air and N_2 atmosphere. It has been shown, that at 450°C the elimination of oxygen during annealing allows an increase in carrier concentration and reduction of the sheet resistance of AZO films four times higher than annealing in ambient air. This effect has not been observed for annealing temperatures below 300°C, where annealing in ambient air proved to have superior influence on the electrical properties. The optical bandgap of all annealed samples was enlarged and for an annealing temperature of 450°C the optical transmission weighted by ASTM G173-03 solar spectrum from 300 to 1100 nm was increased to over 80%. The changes observed in all samples were primarily explained by means of oxygen chemisorption and desorption processes. It is concluded, that oxygen plays an important role in the improvement of electrical and optical properties of AZO thin films during thermal annealing.