Photoelectrochemistry and Drift-Diffusion Simulations in a Polythiophene Film Interfaced with an Electrolyte.

Greta Chiaravalli,Riccardo Sacco,Guglielmo Lanzani,Giovanni Manfredi

doi:10.1021/acsami.1c10158

Abstract

Although the efficiency of organic polymer-based retinal devices has been proved, the interpretation of the working mechanisms that grant photostimulation at the polymer/neuron interface is still a matter of debate. To contribute solving this issue, we focus here on the characterization of the interface between poly(3-hexyltiophene) films and water by the combined use of electrochemistry and mathematical modeling. Simulations well reproduce the buildup of photovoltage (zero current condition) upon illumination of the working electrode made by a polymer film deposited onto an indium tin oxide (ITO) substrate. Due to the essential unipolar transport in the photoexcited film, diffusion leads to a space charge separation that is responsible for the initial photovoltage. Later, electron transfer reactions toward oxygen in the electrolyte extract negative charge from the polymer. In spite of the simple model studied, all of these considerations shed light on the possible coupling mechanisms between the polymeric device and the living cell, supporting the hypothesis of pseudocapacitive coupling.

Highlights

Light is a noninvasive, high-resolution regulatory tool that may find important applications in healing neurodegenerative disorders of the central nervous system or in in vitro studies
We find that the electron transfer to indium tin oxide (ITO) can be neglected
With the combined use of mathematical modeling and electrochemistry, we examined the behavior of a P3HT film sandwiched between an ITO substrate and a saline electrolyte under light excitation

Summary

Introduction

High-resolution regulatory tool that may find important applications in healing neurodegenerative disorders of the central nervous system or in in vitro studies. The general approach consists in the realization of a smart abiotic/biotic interface able to transduce a light stimulus into a bioelectrical[1] or biochemical[2,3] signal Another approach is to use infrared light to perturb the cell membrane dynamical equilibrium.[4] New strategies are based on organic materials and configurations where the external source of energy is light, including the use of nanotechnology.[5−12] Particular interest aroused from the use of a photovoltaic polymer layer to stimulate retinal neurons in vivo.[10] In the proposed device, the poly(3-hexyltiophene) (P3HT) layer establishes a tight contact with the neuron membrane, possibly mediated by a thin solution cleft filled by proteins. We assess the role of oxygen whose concentration in the retina is a matter of debate and can be a crucial parameter in the in vivo experiments.[13]

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Results

Conclusion