%L upm64911 %X The three-terminal heterojunction bipolar transistor solar cell (HBTSC) concept enables the realization of a monolithic double-junction device with individual current extraction. We present an HBTSC realized by a heterojunction of GaInP and GaAs. The one-sun open-circuit voltage (V OC ) of the top and bottom junctions are 1.33 V and 0.99 V, respectively, while fill factors (FF) are above 80%. At one-sun illumination, reducing one junction's bias from V OC to maximum power point degrades the performance of the other junction only slightly (<; 0.5% efficiency loss). These results demonstrate the potential of the HBTSC concept to produce high-efficiency independently connected double-junction solar cells. %A Marius Harry Zehender %A Iván García Vara %A Simon Aurel Svatek %A Myles A. Steiner %A Pablo García Linares %A Emily Warren %A Adele Tamboli %A Antonio Martí Vega %A Elisa Antolín Fernández %R 10.1109/PVSC40753.2019.8980563 %I IEEE %K Double junction; multi terminal; independent current; photovoltaic cells; gallium indium phosphide; gallium arsenide %C Chicago, IL, USA %T Demonstrating the GaInP/GaAs three-terminal Heterojunction Bipolar Transistor Solar Cell %D 2019 %P 35-40 %B 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC)