A modified dye-sensitized solar cell consisting of a thin TiO₂ barrier layer sensitized with natural trimeric light-harvesting complex II (LHCII) from spinach was used as a biomimetic model to study the effects of LHCII aggregation on the photovoltaic properties. The aggregation of individual trimers induced molecular reorganization, which dramatically increased the photocurrent. The morphology of small- and large-size LHCII aggregates deposited on a surface was confirmed by atomic force microscopy. Enhanced LHCII immobilization was accomplished via electrostatic interaction with amine-functionalized photoanodes. The photocurrent responses of the assembled solar cells under illumination at three characteristic wavelength bands in the UV-Vis absorption spectra of LHCII solutions confirmed that a significant photocurrent was generated by LHCII photosensitizers. The enhanced photocurrent by large aggregated LHCII is shown to correlate with the quenching in the far-red fluorescence deriving from chlorophyll–chlorophyll charge transfer states that are effectively coupled with the TiO₂ surface and thus inject electrons into the TiO₂ conduction band. The large aggregated LHCII with more chlorophyll–chlorophyll charge transfer states is a much better sensitizer since it injects electrons more efficiently into the conduction band of TiO₂ than the small aggregated LHCII mostly consisting of unquenched chlorophyll excited state. The assembled solar cells demonstrated remarkable stability in both aqueous buffer and acetonitrile electrolytes over 30 days.