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In photovoltaic (PV) panels consisting of multiple substrings connected in series, mismatch in substring characteristics due to partial shading causes the significant reduction in energy yield and the occurrence of multiple maximum power points. In solar roofs of plug-in hybrid electric vehicles (PHEVs), substring characteristics are always unavoidably mismatched due to the curvature of solar roofs, resulting in the mismatch issues similar to partial shading. Various kinds of differential power processing (DPP) converters have been proposed to preclude mismatch issues in traditional flat PV panels. The key contributions and novelties of this paper are summarized as follows. Firstly, uneven irradiance on the solar roof of Prius PHEVs is investigated. Secondly, existing DPP converter architectures are reviewed to select a proper DPP converter topology for PHEV applications. Thirdly, the selected topology is improved to be better suitable for PHEV applications, followed by the detailed operation analysis. Lastly, the experimental results of the laboratory and field testing using a prototype are presented. Field testing using an actual solar roof of Prius PHEV was performed, and the results demonstrated the daily energy yield enhancement of 4%–5% by the proposed DPP converter.