The behavior or amorphous silicon parallel to micro crystalline silicon (a-Si parallel to mu c-Si) tandem-type photovoltaic (PV) module is complex because the output current is limited by the lower current component cell. Also, the outdoor behaviors are not fully understood. The impact of environment factors on solar cell parameters of a-Si parallel to mu c-Si PV module was quantitatively analyzed and the module was compared with other silicon-based PV modules (single crystalline silicon (sc-Si) and amorphous silicon (a-Si)). The contour maps of solar cell parameters were constructed as a function or irradiance and module temperature. The contour map of a-Si parallel to mu c-Si PV modules is similar to that of a-Si modules. The results imply that output characteristics of a-Si parallel to mu c-Si PV modules are mainly influenced by the a-Si top cell. Furthermore, the efficiency of a-Si parallel to mu c-Si PV modules was compared other solar cell parameters and the contour map of efficiency is similar to that of fill factor. (C) 2008 Elsevier B.V. All rights reserved.