Biointerfaces based on photovoltaic substrates has gained substantial attention for neural photostimulation[1, 2]. The control of Faradaic and capacitive charge transfer mechanisms by these substrates is important for effective and safe photostimulation of neurons. Faradaic mechanism uses charge transfer between electrode and electrolyte with oxidation and reduction reactions, and capacitive mechanism electrostatically perturb local ion concentration in the electrode/electrolyte interface[3, 4]. In this study, we show the control of light-activated Faradaic and capacitive charge transfer mechanisms by bulk heterojunction photovoltaic biointerfaces. We tuned the strength of the mechanisms via spatial control of the photogenerated electrons and holes in the biointerface architecture. For that, we explored three different architectures (Fig. 1) using intermediate ZnO and MoOx layers and without any intermediate layer between the transparent metal oxide (ITO) and photoactive layer. The photoactive layer is composed of organic-inorganic ternary blend of poly(3-hexylthiophene-2,5-diyl (P3HT), [6,6]-Phenyl-C61-butyric acid methyl ester (PCBM) and PbS quantum dots that lead to strong displacement currents. Moreover, we observed that integration of PbS quantum dots in the active blend of P3HT:PCBM enhances both capacitive and faradaic photocurrents due to well-aligned energy diagram, stronger absorption and better surface morphology. To characterize the photostimulation, we seeded SHSY-5Y cells on our biointerfaces and recorded the membrane depolarization of single cells. The results are also supported by two-domain stimulation model[4, 5].
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