Enzo Menna

Carbon nanotubes and organic solar cells

The use of carbon nanotubes in photovoltaics is still challenging due to different issues connected to their synthesis, purification, functionalization, processing and device integration. From this perspective at first we review on selected contributions dealing with the above issues; then we focus on the advantages and limitations of carbon nanotubes for the development of organic solar cells.

Microwave‐Assisted Synthesis of a Soluble Single Wall Carbon Nanotube Derivative

Abstract The development of a novel procedure based on microwave (MW) heating allowed to obtain a soluble derivative of Single Wall Carbon Nanotubes (SWNTs) by grafting poly(ethylene glycol) (PEG) chains to shortened SWNTs. The use of MW irradiation remarkably enhanced reaction rates compared to similar syntheses based on conventional heating.

Solar cells based on a fullerene–azothiophene dyad

A power conversion efficiency of 0.37%, under white light of 80 mW cm-2 intensity, was obtained when a fullerene-azothiophene dyad was used as the active layer of a photovoltaic cell.

One-pot self-assembly of mesostructured silica films and membranes functionalised with fullerene derivatives

Three fullerene derivatives have been employed with amphiphilic block copolymers both as structure-directing agents and doping molecules in one-pot synthesis of self-assembled 2D-hexagonal and cubic porous silica mesostructures, in the form of bulk materials, thick cast films and thin films through an evaporation-induced self-assembling procedure. Thermal calcination of the samples at 280 °C almost completely removed the block copolymer from the silica matrix without substantial loss of the fullerene additive, as demonstrated by FT-Raman spectra in which a clear signature of the fullerene Ag mode at 1467 cm−1 was still clearly observed. Upon irradiation with laser light at 632.8 nm, the fullerene-doped mesostructured materials exhibited photoluminescence at room temperature, which was not observed in the silica matrix.

Electropolymerization and spectroscopic properties of a novel double-cable polythiophene with pendant fullerenes for photovoltaic applications

A novel double-cable polythiophene carrying fullerene side groups has been prepared electrochemically. Electrochemical and spectroscopic data show that this bipolar material, where phase separation cannot occur, retains the favorable optoelectronic properties of polythiophene/fullerene blends. Excited state spectroscopy reveals clear evidence of a photo-induced electron transfer from the donor cable (polythiophene) to the pendant acceptor cable (fullerene substituents).

The continuous-flow cycloaddition of azomethine ylides to carbon nanotubes

This communication demonstrates a straightforward continuous-flow method for efficient exohedral functionalisation of carbon nanotubes which affords soluble samples in a much shorter time over conventional batch processing.

Investigation of the Inner Environment of Carbon Nanotubes with a Fullerene‐Nitroxide Probe

A fulleropyrrolidine bearing a nitroxide free radical has been inserted into single-walled carbon nanotubes with the aid of supercritical CO2. Thanks to the encapsulated paramagnetic probes, it has been possible to detect and characterize the resulting peapod-like structure through electron paramagnetic resonance (EPR) spectroscopy. In particular, the analysis of spectral parameters derived from extensive EPR studies has elucidated the orientation and the residual rotational dynamics of the molecules embedded in the nanotubes. A limited anisotropic rotational freedom of the encapsulated fullerene nitroxide reveals a rather strong interaction of the probe with the surrounding nanotube walls. The interaction seems to involve the fullerene cage (as confirmed by Raman spectroscopy) and not the nitroxide moiety, whose EPR spectral characteristics, such as the isotropic hyperfine constant and the g-tensor, remain unaltered after encapsulation.

Enhanced neuronal cell differentiation combining biomimetic peptides and a carbon nanotube-polymer scaffold

Carbon nanotubes are attractive candidates for the development of scaffolds able to support neuronal growth and differentiation thanks to their ability to conduct electrical stimuli, to interface with cells and to mimic the neural environment. We developed a biocompatible composite scaffold, consisting of multi-walled carbon nanotubes dispersed in a poly-L-lactic acid matrix able to support growth and differentiation of human neuronal cells. Moreover, to mimic guidance cues from the neural environment, we also designed synthetic peptides, derived from L1 and LINGO1 proteins. Such peptides could positively modulate neuronal differentiation, which is synergistically improved by the combination of the nanocomposite scaffold and the peptides, thus suggesting a prototype for the development of implants for long-term neuronal growth and differentiation. From the clinical editor: The study describes the design and preparation of nanocomposite scaffolds with multi-walled carbon nanotubes in a poly-L-lactic acid matrix. This compound used in combination with peptides leads to synergistic effects in supporting neuronal cell growth and differentiation.

A fullerene-azothiophene dyad for photovoltaics

Abstract A fullerene-azothiophene donor–acceptor dyad is proposed as a photoactive material for organic solar cells. The photophysical characteristics and the structural properties of films of the dyad are investigated with time-resolved EPR (TREPR) and X-ray diffraction measurements. Solar cells made from the dyad were fabricated and their photovoltaic performance evaluated in function of the active layer thickness.

Functionalization of transparent conductive oxide electrode for TiO2-free perovskite solar cells

Many of the best performing solar cells based on perovskite-halide light absorbers use TiO2 as an electron selective contact layer. However, TiO2 usually requires high temperature sintering, is related to electrical instabilities in perovskite solar cells, and causes cell performance degradation under full solar spectrum illumination. Here we demonstrate an alternative approach based on the modification of transparent conductive oxide electrodes with self-assembled siloxane-functionalized fullerene molecules, eliminating TiO2 or any other additional electron transporting layer. We demonstrate that these molecules spontaneously form a homogenous monolayer acting as an electron selective layer on top of the fluorine doped tin oxide (FTO) electrode, minimizing material consumption. We find that the fullerene-modified FTO is a robust, chemically inert charge selective contact for perovskite based solar cells, which can reach 15% of stabilised power conversion efficiency in a flat junction device architecture using a scalable, low temperature, and reliable process. In contrast to TiO2, devices employing a molecularly thin functionalized fullerene layer show unaffected performance after 67 h of UV light exposure.