The development of solution-processed hybrid organic-inorganic heterojunction solar cells have provoked increasing research effort due to potential to significantly reduce the fabrication cost of semiconductor solar cells while maintaining the high power conversion efficiency (PCE). With a recent record of GaAs solar cells achieving 28.8% via a wafer lift-off technique, hybrid organic/GaAs solar cells can offer an alternative route to provide more affordable solar power than current semiconductor technologies. In this work, we demonstrate the hybrid devices based on a conductive polymer poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) directly spun-cast on planar gallium arsenide materials. While still lacking for optimized antireflection, the PCE of the best performing device can achieve nearly 10% by introducing the monolayer graphene as transparent electrode. The current progress presents 2-fold enhancement in comparison to a previous record at 5% based on GaAs nanowire templates.