The series resistance of an InGaP/InGaAs/Ge triple-junction solar cell was evaluated in detail. Series resistance components such as electrode resistance, tunnel junction resistance and lateral resistance between electrodes were estimated separately. The characteristics of the triple-junction solar cell under concentrated light were evaluated by equivalent circuit calculation with a simulation program with integrated circuit emphasis (SPICE). By equivalent circuit calculation, the optimization of cell designs was performed, focusing on series resistance and cell current in order to realize high-efficiency concentrator cells. (c) 2005 Elsevier B.V. All rights reserved.