Monolithic Ga0.49In0.51P/GaAs cascade solar cells, with a p(+)/n(+) GaAs tunnel junction were grown by MOCVD technique. The variation of the photovoltage, photocurrent, fill factor, efficiency, I-V characteristics and spectral response under different temperatures (25-75degreesC), and light intensity values (1-40 sun), were investigated experimentally. The open-circuit voltage of the multijunction cell decreases with the temperature increase at a rate. of 5.5 mV/degreesC. The efficiency of the cascade structure under investigation was increased with an increase in the light concentration up to a point where the series resistance and the tunnel junction effects become significant. (C) 2002 Elsevier Science Ltd. All rights reserved.