Bifacial photovoltaics and multijunction systems represent the most promising alternatives to overcome the theoretical limit of single-junction Si photovoltaics, and these solutions can also be combined to achieve higher performances. This work investigates the outdoor performance of a bifacial four-terminal photovoltaic system based on combining a III-V semiconductor with the silicon heterojunction technology. By exploiting the wide band gap energy of GaAs, the bifaciality of the Si heterojunction and the spectrum-splitting capability of dichroic mirrors, an optimal voltage match between mini-modules of the two solar cells was achieved, with an open-circuit voltage mismatch of 4% of the average value. In this study, we demonstrate the full functionality of bifacial operation with a 17% increase of power conversion efficiency throughout the day compared to monofacial operation. Furthermore, we show that though the …