In this work, based on the advanced commercial software, the Crosslight APSYS with improved tunnel junction model, two-dimensional (2D) simulation has been performed on the triple-junction (TJ) GaInP/GaAs/Ge solar cell devices. The APSYS simulator solves several interwoven equations including the basic Poisson's equation, and drift-diffusion current equations for electrons and holes. The model of tunnel junction with the equivalent mobility enables an efficient modeling of multi-junction solar cell across the whole solar spectra, where all the spectrum data points are processed by taking into account the effects of multiple layer optical interference and photon generation. Basic physical quantities like band diagrams, optical absorption and generation are demonstrated. The modeled IV characteristics and offset voltage agree well with the published experimental results for TJ GaInP/GaAs/Ge solar cell device. The quantum efficiency spectra have also been computed for the modeled TJ solar cell device. Possible design optimization issues to enhance the quantum efficiency have also been discussed with respect to some applicable features of Crosslight APSYS.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.