Abstract The performance of InP solar cells has been limited by low open‐circuit voltages. While the reported short‐circuit current densities are approaching the theoretical limit, the open‐circuit voltages have yet to obtain what is expected from a semiconductor with a direct band gap of 1.35 eV. This work investigates the factors that determine the open‐circuit voltage and presents the design and fabrication of a novel high open‐circuit voltage p‐n InP solar cell. the key aspect of the novel design is a complete analysis of the top contact metallization effects on the reverse saturation current density and the open‐circuit voltage. the features of the design are not specific to InP solar cells but are applicable to other advanced material solar cells that require a thin emitter for an optimal design (those materials with a high absorption coefficient). By minimizing the reverse saturation current density, a high open‐circuit voltage and high efficiency may be obtained. In addition, a complete analysis of the solar cell modelling is provided, with comparisons to other published InP solar cell models and device results to juxtapose the key material and design parameter effects.