Characteristics of Al0.36Ga0.64As/GaAs tandem solar cells with new type pp(-)n(-)n structural AlGaAs top cells are reported. A tunnel junction consisting of a p(+)-GaAs layer and an n(+)-Al0.15Ga0.85As layer is used for the interconnection. This brings about a good result on two critical points: the light absorption and the degradation of current-voltage (I-V) characteristics by heat treatment during the growth of the AlGaAs cell structure. A tandem solar cell design focusing on the current matching between the top and bottom cells leads to a 27.6% efficiency with a fabricated Al0.36Ga0.64As/GaAs tandem solar cell under 1 sun, AM 1.5 global conditions. (C) 2001 Elsevier Science B.V. All rights reserved.