Study of working pressure on the optoelectrical properties of Al-Y codoped ZnO thin-film deposited using DC magnetron sputtering for solar cell applications

Low cost transparent conductive Al-Y codoped ZnO (AZOY) thin-films were prepared on a glass substrate using a DC magnetron sputtering technique with various working pressures in the range of 5-13 mTorr. The relationship among the structural, electrical, and optical properties of sputtered AZOY films was studied as a function of working pressure. The XRD measurements show that the crystallinity of the films degraded as the working gas pressure increased. The AZOY thin-film deposited at a working pressure of 5 mTorr exhibited the lowest electrical resistivity of 4.3 × 10−4 Ω cm, carrier mobility of 30 cm2/V s, highest carrier concentration of 4.9 × 1020 cm−3, and high transmittance in the visible region (400-800 nm) of approximately 90%. Compared with Al doped ZnO (AZO) thin-films deposited using DC or RF magnetron sputtering methods, a high carrier mobility was observed in our AZOY thin-films. This result can be used to effectively decrease the absorption of near infrared-rays in solar cell applications. The mechanisms are attributed to the larger transition energy between Ar atoms and sputtering particles and the size compensation of the dopants. Finally, the optimal quality AZOY thin-film was used as an emitter layer (or window layer) to form AZOY/n-Si heterojunction solar cells, which exhibited a stable conversion efficiency (η) of 9.4% under an AM1.5 illumination condition.