To enhance the performance of tandem-type III–V compound multijunction solar cells, the transparent indium-tin-oxide (ITO) film was used to replace conventional metal electrode for increasing the incident light area. For performing ohmic contact between the n-AlInP window layer and the ITO film, a transition layer of Au/AuGeNi thin metals was used and investigated. Besides, to improve ohmic performance and to passivate the surface states, (NH4)2Sx surface treatment was used. The conversion efficiency of the (NH4)2Sx-treated triple-junction solar cells was increased more than 3.09%. Furthermore, an improved oblique SiO2/SiO2/ITO triple antireflection structure was designed to reduce the reflectivity of illuminating sunlight. The conversion efficiency of the (NH4)2Sx-treated triple-junction solar cell with improved antireflection structure could be improved more than 4.23%. Simple and effective approaches were designed to improve the performances of tandem-type III–V triple-junction solar cells. Copyright © 2010 John Wiley & Sons, Ltd.