This study investigates the junction formation and interface properties of PEDOT:PSS/n-GaAs hybrid solar cells on planar GaAs substrates. Barrier height, photocurrent, dark saturation current and build-in potential at this hybrid interface are measured by varying n-GaAs doping concentrations. The work function and valence band edge of the polymer are extracted from ultraviolet photoelectron spectroscopy to construct the band diagram of the hybrid n-GaAs/PEDOT:PSS junction. The current-voltage characteristics were analyzed by using abrupt (p+n) junction and Schottky junction models. Contrary to the earlier results from the PEDOT:PSS/n-Si solar cells, the experimental evidence clearly suggested that the interface between n-GaAs and PEDOT:PSS more likely exhibited a Schottky type instead of a p+n junction. The current transport is governed by the thermionic emission of majority carriers over a barrier and not by diffusion. The dark saturation current density increases markedly owing to the increasing surface recombination rate in heavier n-doped GaAs substrates, leading to significant deterioration in solar cells performance.