• microfabrication
• near-infrared
• neurostimulation
• organic conductive polymers
• photovoltaic pixel
• wireless neural implants

Neural implants have the potential to revolutionize the treatment of a wide range of neurological conditions, such as blindness, deafness, Parkinson’s disease and Alzheimer. However, long term implantation is hampered by the mechanical mismatch between implanted components and nervous tissue, which exacerbates the foreign body reaction. Wireless neural implants represent a straightforward approach to dispose of bulky and rigid components such as batteries and stimulator. Among the different wireless power technologies, photovoltaics (PV) is particularly appealing for prosthetic vision applications, as it is conceptually similar to how photoreceptors function in the human eye. With respect to inorganic PV semiconductors, which are stiff and require high temperature processing, organic PV semiconductive polymers offer integration into existing microfabricated polymeric implants, with the accompanying flexibility and softness for seamless interaction with nervous tissue. This Master Thesis project aimed at developing a Near Infrared (NIR)-sensitive photovoltaic pixel for neurostimulation. λ = 850nm was selected as stimulation wavelength, since optical transmittance of biological tissues is highest in the NIR and human eye photoreceptors do not perceive wavelengths above 800nm. To achieve the final goal, two different polymeric blends, PDPP3T:PC70BM and PDPP3T:ITIC, were tested. A robust manufacturing process was developed to obtain reliable devices. The photovoltaic cells obtained were characterized by measuring JV curves and efficiency. The most promising solar cell configuration, ITO/ZnO/PDPP3T:ITIC (1:2 v/v%)/NiO/Pt was further optimized both in terms of solar cell stack and post-treatments. In particular, IrOx-Ir adhesion layers proved to solve the delamination problems experienced by the first devices generation at NiO-Pt interface, while exposure under UV light had a positive impact on the JV curve shape and performances. The solar cell developed matches the proposed application requirements and it is therefore ready to be tested in the final implant configuration to validate the stimulation capabilities.