Computational modeling of ITO/P3HT/aqueous electrolyte interfaces for energy and biological applications

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Oral, Paolo Salvatori, presentation 086
Publication date: 5th February 2015

Over the past two decades, the science and engineering of organic semiconducting materials have advanced very rapidly, leading to the demonstration and optimization of a range of organic-based solid-state devices, including organic light-emitting diodes (OLEDs), field-effect transistors, photodiodes, and photovoltaic cells.¹ More recently, a number of new applications ranging from bioelectronics² to water splitting devices³ has been developed, requiring the use of liquid electrolytes at the interface with a photoactive polymer. A fully understanding of these complex interfaces is crucial in order to rationalize and optimize the electron/energy transfer processes occurring at the heart of the device. In this talk I will present our recent findings on the simulation of an ITO/P3HT/water devices (Figure 1). This materials combination has been recently employed with promising results both in photo-catalytic cells for hydrogen generation⁴ and in biological devices for neural stimulation, that could be used for new generation in vivo retinal prosthesis.⁵ Despite the great actuality of these topics, these systems are essentially unexplored from the computational side. The global picture of our investigation show that the ITO/P3HT/water interface well performs for the splitting of photogenerated charge carriers (Figure 1).On one side, the electrolyte is able to polarize the outermost layer of the organic semiconductor, preferentially localizing the photogenerated electrons at the polymer/solution interface. On the other hand, in good agreement with a previous experimental work,⁶ holes can be transferred to the ITO substrate. This charge dissociation process plays a fundamental role in the exploitation of the operational mechanism of the considered devices.
Figure 1. Surface plot of the density of states (left) of the valence and conduction bands for the layer model of P3HT interfaced with ITO and water (right). The splitting of the photogenerated charge carriers is highlighted, with the electrons preferentially accumulated at the polymer/water interface and the holes transferred to the ITO substrate.
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