The nitrogen and aluminium-codoped ZnO (NAZO) thin films are grown by rf magnetron sputtering system with the nitrogen flow ratio changing from 0% to 30%. All of the NAZO films show a strongly c-axis preferred orientation, while the values of the electron concentration are found to decrease with the increase of the nitrogen flow ratio, and they are determined as 1.5-27 x 10(19) cm (3). The optical transmittance spectra indicate an average transmittance of about 95% in the visible range, and a red shift of the band gap energy is observed with increasing the nitrogen flow ratio. These results suggest that the nitrogen flow ratio is an important parameter to grow the high-quality NAZO films for the application of solar cells. (C) 2010 Elsevier B. V. All rights reserved.