Sebastiano Bellani

A polymer optoelectronic interface restores light sensitivity in blind rat retinas

Interfacing organic electronics with biological substrates offers new possibilities for biotechnology due to the beneficial properties exhibited by organic conducting polymers. These polymers have been used for cellular interfaces in several fashions, including cellular scaffolds, neural probes, biosensors and actuators for drug release. Recently, an organic photovoltaic blend has been exploited for neuronal stimulation via a photo-excitation process. Here, we document the use of a single-component organic film of poly(3-hexylthiophene) (P3HT) to trigger neuronal firing upon illumination. Moreover, we demonstrate that this bio-organic interface restored light sensitivity in explants of rat retinas with light-induced photoreceptor degeneration. These findings suggest that all-organic devices may play an important future role in sub-retinal prosthetic implants.

Organic photoelectrochemical cells with quantitative photocarrier conversion

Efficient solar-to-fuel conversion could be a cost-effective way to power the planet using sunlight. Herein, we demonstrate that Organic Photoelectrochemical Cells (OPECs) constitute a versatile platform for the efficient production of solar fuels. We show that the photogenerated carriers at the organic active layer can be quantitatively extracted to drive photoelectrochemical reactions at the interface with a liquid solution. Indeed, an unprecedented photocurrent of 4 mA cm−2 is extracted for an OPEC device, comparable to that of a solid-state device with similar optical properties. Through the careful choice of the selective contact and the redox couple in the liquid medium, we can tune the energetics of the system and activate either oxidative or reductive chemistry. The design rules to drive the desired electrochemical reaction are provided based on a comprehensive study of the energetic aspects of OPEC configuration. Finally, we demonstrate that OPEC devices effectively produce hydrogen in acetonitrile when a cobaloxime based homogeneous catalyst is present in the solution, and HCl is used a source of protons.

Hybrid organic–inorganic H2-evolving photocathodes: understanding the route towards high performance organic photoelectrochemical water splitting

A promising, yet challenging, route towards renewable production of hydrogen is the direct conversion of solar energy at a simple and low cost semiconductor/water junction. Despite the theoretical simplicity of such a photoelectrochemical device, different limitations among candidate semiconductor materials have hindered its development. After many decades of research on inorganic semiconductors, a conclusive solution still appears out of reach. Here, we report an efficient hybrid organic–inorganic H2 evolving photocathode, consisting of a donor/acceptor blend sandwiched between charge-selective layers and a thin electrocatalyst layer. The role and stability of the different interfaces are investigated, and the conductive polymer is proven to be an efficient material for a semiconductor/liquid PEC junction. The best performing electrodes show high performances with a photocurrent of 3 mA cm−2 at 0 V vs. RHE, optimal process stability with 100% faradaic efficiency during electrodes lifetime, excellent energetics with +0.67 V vs. RHE onset potential, promising operational activity of several hours and by-design compatibility for implementation in a tandem architecture. This work demonstrates organic semiconductors as a radically new option for efficient direct conversion of solar energy into fuels, and points out the route towards high performance organic photoelectrochemical water splitting.

Polymer-based photocathodes with a solution-processable cuprous iodide anode layer and a polyethyleneimine protective coating

Organic semiconductors have been proven to be suitable for efficient photovoltaic generation during the last decade but have been scarcely assessed as photoelectrochemical devices. In this work we present the fabrication and characterization of a new efficient hybrid organic/inorganic photocathode for hydrogen evolution showing both a positive onset potential (+0.702 V vs. RHE) and a maximum power point (+0.303 V vs. RHE). We demonstrate that a conventional P3HT:PCBM bulk heterojunction architecture enclosed between a solution-processed cuprous iodide hole selective layer and a Pt-decorated nanostructured TiO2 layer can efficiently photogenerate hydrogen under acidic conditions under simulated 1 Sun illumination. This architecture showed initial photocurrents as high as 8 mA cm−2 at 0 V vs. RHE, IPCE above 50%, 100% faradaic efficiency and an ideal ratiometric power-saved figure of merit equal to 1.21%. Finally, with the addition of a solution-processed polyethyleneimine protective coating, we improved the device stability. This work paves the way to the use of hybrid organic/inorganic photocathodes for efficient solar hydrogen generation.

Few-layer MoS2 flakes as a hole-selective layer for solution-processed hybrid organic hydrogen-evolving photocathodes

High-efficiency organic photocathodes, based on a regioregular poly(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (rr-P3HT:PCBM) bulk heterojunction sandwiched between charge-selective layers, are emerging as efficient and low-cost devices for solar hydrogen production by water splitting. Nevertheless, stability issues of the materials used as charge-selective layers are hampering the realization of long-lasting photoelectrodes, pointing out the need to investigate novel and stable materials. Here, we propose MoS2 flakes, produced by Li-aided exfoliation of the bulk counterpart, as an efficient atomic-thick hole-selective layer for rr-P3HT:PCBM-based photocathodes. We carried out p-type chemical doping to tune on-demand the MoS2 Fermi level in order to match the highest occupied molecular orbital level of the rr-P3HT, thus easing the hole collection at the electrode. The as-prepared p-doped MoS2-based photocathodes reached a photocurrent of 1.21 mA cm−2 at 0 V vs. RHE, a positive onset potential of 0.56 V vs. RHE and a power-saved figure of merit of 0.43%, showing a 6.1-fold increase with respect to pristine MoS2-based photocathodes, under simulated 1 sun illumination. Operational activity of the photocathodes over time and under 1 sun illumination revealed a progressive stabilization of the photocurrents at 0.49 mA cm−2 at 0 V vs. RHE. These results pave the way towards the exploitation of layered crystals as efficiency-boosters for scalable hybrid organic H2-evolving photoelectrochemical cells.

Synthesis of modified fullerenes for oxygen reduction reactions

The oxygen reduction reaction (ORR) is a key process common in several energy converting systems or electro-chemical technologies such as fuel cells, metal–air batteries, oxygen sensors, etc., which is based on the use of expensive and scarcely available platinum metal. In the search for carbon-based catalysts for ORRs, two different classes of new fullerene hybrids and metal-free fullerene derivatives endowed with suitable active sites have been prepared by highly selective metal- and organo-catalyzed synthetic methodologies. Along with their classical behavior as electron acceptors in polymer-based photo-electrochemical cells, the new fullerene derivatives are able to efficiently catalyze ORRs by using no metals or very low amounts of metals. Remarkably, the activity of metal-free fullerenes has proved to be as high as that observed for metallofullerenes bearing noble metals, and up to ten-fold higher than that of PCBM.

Field-effect and capacitive properties of water-gated transistors based on polythiophene derivatives

Recently, water-gated organic field-effect transistors (WGOFET) have been intensively studied for their application in the biological field. Surprisingly, a very limited number of conjugated polymers have been reported so far. Here, we systematically explore a series of polythiophene derivatives, presenting different alkyl side chains lengths and orientation, and characterized by various morphologies: comparative evaluation of their performances allows highlighting the critical role played by alkyl side chains, which significantly affects the polymer/water interface capacitance. Reported results provide useful guidelines towards further development of WGOFETs and represent a step forward in the understanding of the polymer/water interface phenomena.

Conjugated polymers for the optical control of the electrical activity of living cells

The possibility to optically excite the electrical activity of living cells by using exogenous absorbers is gaining more and more interest in the neuroscience and biotechnology community. Conjugated polymers, inherently sensitive to visible light, were recently proposed as candidates to this goal. To date, however, only one polymer type, namely regio-regular poly-3-hexylthiophene, has been tested as the active material. In this work four different conjugated polymers, regarded as prototypes of their category, are investigated as photoactive bio-interfaces. The selected materials have different absorption spectra, morphology, light emission efficiency and charge transport properties. We analyze their key-enabling properties, such as electrochemical stability, surface morphology, wettability, sterilization compatibility, interaction with protein adhesion layers and toxicity, throughout all the necessary steps for the realization of an efficient bio-optical interface. We demonstrate that all considered polymers are characterized by good biocompatibility and cell seeding properties, and can optimally sustain thermal sterilization. Conversely, electrochemical stability and cell photostimulation efficacy can vary a lot among different materials, and should be carefully evaluated case by case. Reported results represent the starting point for the implementation of bio-polymer interfaces sensitive to different colors and, in perspective, for the realization of a three-chromatic artificial visual prosthesis.

Stabilizing organic photocathodes by low-temperature atomic layer deposition of TiO2

Organic semiconductor light absorbers are receiving attention for their potential application in photoelectrochemical (PEC) cells for renewable fuels generation. Key to their advancement is precise control of the interfaces between charge-selective contacts, absorber layers, and electrocatalysts, while maintaining compatibility with an aqueous electrolyte environment. Here we demonstrate a new process for low-temperature atomic layer deposition (ALD) of TiO2 onto a P3HT:PCBM polymer blend surface for stable high-performance organic PEC photocathodes. This ALD TiO2 layer provides three key functions: (1) formation of an electron-selective contact to the polymer to enable photovoltage and photocurrent generation, (2) a robust interface for conducting charge between the photoabsorber and electrocatalyst layers, and (3) a pinhole-free barrier to water penetration, preventing corrosion of the underlying materials. The resulting device based on the architecture CuI/P3HT:PCBM/TiO2/RuOx showed excellent performance and stability during PEC hydrogen-evolution. More broadly, the achievement of ALD film formation on a polymer surface opens doors in the field of functional organic–inorganic electronic interfaces.

Solution-Processed Hybrid Graphene Flake/2H-MoS2 Quantum Dot Heterostructures for Efficient Electrochemical Hydrogen Evolution

We designed solution-processed, flexible hybrid graphene flake/2H-MoS2 quantum dot (QD) heterostructures, showing enhanced electrocatalytic activity for the hydrogen evolution reaction (HER) with respect to their native individual components. The 2H-MoS2 QDs are produced through a scalable, environmentally friendly, one-step solvothermal approach from two-dimensional (2D) 2H-MoS2 flakes obtained by liquid phase exfoliation (LPE) of their bulk counterpart in 2-Propanol. This QDs synthesis avoids the use of high boiling point and/or toxic solvents. Graphene flakes are produced by LPE of graphite in N-Methyl-2-pyrrolidone. The electrochemical properties of 2H-MoS2 QDs and their HER-favorable chemical and electronic coupling with graphene enable to reach current density of 10 mA/cm² at an overpotential of 136 mV, surpassing the performances of graphene flake/2H-MoS2 (1T-MoS2) flake heterostructures. Our approach provides a shortcut, viable and cost-effective method for enhancing the 2D materials electrocataly...