DHICA ion-modified melanin based porous Si solar cell
This work studies photosensitivity and current-voltage characteristics under illumination of water-soluble eumelanin films based on DHICA tetramers and hybrid eumelanin/porous Si photovoltaic cells aimed at optimizing their characteristics. By using DMSO to dissolve melanin containing protonated carboxyl groups and to remove ammonium cations, it became possible to significantly reduce the ionic component of conductivity, thus improved the electron transport. It was found out that dissolution in DMSO provides a denser {\pi}-{\pi} stacking of DHICA tetramers, which led to a significant improvement in the photovoltaic cell parameters. In particular, the efficiency increased from 0.023 % to 4.4 % and the series resistance decreased from 119 {\Omega} to 42.6 {\Omega}. Modeling demonstrated that high-temperature annealing, which causes decarboxylation, leads to a structural rearrangement of tetramers from a Christmas tree-like configuration to a "toothed helix". At this, one of the planes partially straightens. This emphasizes the critical importance of the morphology of the organic layer for photogeneration of carriers in a heterojunction.