Camillo Sartorio

On the trade-off between processability and opto-electronic properties of single wall carbon nanotube derivatives in thin film heterojunctions

A flow functionalization route has been employed to derivatize single wall carbon nanotubes (SWCNTs) by thienylphenyl groups. The SWCNT derivatives in the most soluble fraction have been characterized by thermogravimetric analysis, DLS analysis, DFT calculations, and UV-vis-NIR, microRaman and IR spectroscopies to study the degree of functionalization, the concentration of SWCNTs in solution, the dimension of the aggregates in solutions, the density of defects, and the presence of the thienylphenyl groups. Thin-film heterojunctions made of SWCNT derivatives and poly(3-hexylthiophene) (P3HT) have been prepared by various methods employing the Langmuir–Schaefer technique, spin-coating and thermal annealing processes. By comparing the batch and the flow functionalizations, a trade-off between solubility, processability and the thin-film opto-electronic properties has been found as a result of the degree of functionalization.

Exploring the Interplay Between Ligand Derivatisation and Cation Type in the Assembly of Hybrid Polyoxometalate Mn-Andersons

Herein a library of hybrid Mn-Anderson polyoxometalates anions are presented: 1, [(MnMo6 O18 )((OCH2 )3 -C-(CH2 )7 CHCH2 )2 ](3-) ; compound 2, [(MnMo6 O18 )((OCH2 )3 C-NHCH2 C16 H9 )2 ](3-) ; compound 3, [(MnMo6 O18 )((OCH2 )3 C-(CH2 )7 CHCH2 )1 ((OCH2 )3 C-NHCH2 C16 H9 )1 ](3-) ; compound 4, [(MnMo6 O18 )((OCH2 )3 C-NHC(O)CH2 CHCH2 )2 ](3-) and compounds 5-9, [(MnMo6 O18 )((OCH2 )3 C-NHC(O)(CH2 )x CH3 )2 ]), where x = 4, 10, 12, 14, and 18 respectively. The compounds resulting from the cation exchange of the anions 1-9 to give TBA (a) and DMDOA (b) salts, and additionally for compounds 1, 2 and 3, tetraphenylphosphonium (PPh4 ) (c) salts, are explored at the air/water interface using scanning force microscopy, showing a range of architectures including hexagonal structures, nanofibers and other supramolecular forms. Additionally the solid-state structures for compounds 1c, 2c, 4a, 6a, 9a, are presented for the first time and these investigations demonstrate the delicate interplay between the structure of the covalently derivatised hybrid organo-clusters as well as the ion-exchange cation types.

Enhanced power-conversion efficiency in organic solar cells incorporating copolymeric phase-separation modulators

A new class of copolymers containing oligothiophene moieties with different lengths and fullerene units have been designed and prepared by an easy and inexpensive one-step synthetic approach. The incorporation of small quantities of these copolymers into bulk heterojunction (BHJ) solar cells with donor regioregular polythiophene (P3HT) and an acceptor fullerene derivate (PCBM) results in good control of the phase separation process without further affecting the BHJ optoelectronic properties. Indeed, under thermal annealing these copolymers allow the modulation of the growth of domains whose size depends on the length of the copolymer repetitive units. Domain size on the same length scale as the P3HT exciton diffusion length with a good continuity between the electrodes gives efficient exciton dissociation and charge mobility. Thus by employing copolymers containing oligothiophenic chains with a size of about 8 nm, the power conversion efficiency (PCE) (4.46%) and short current density (JSC) (16.15 mA cm−2) values are the highest reported so far for P3HT:PCBM solar cells on plastic substrates.

Electrodeposition of novel poly(naphthalenediimide-quaterthiophene) thin films and applications in plastic optoelectronics devices

A novel symmetric naphthalenediimide-quaterthiophene derivative (NDIT4d) has been polymerized on different substrates including glassy carbon and ITO/PET electrodes by means of electrochemical methods. XPS and UV-VIS spectroscopy as well as cyclic voltammetry have been employed for characterizing the thin film chemical features, the band gap and the HOMO and LUMO levels. DFT computational studies were in close agreement with the experimental observables also showing intriguing geometrical effects on the band gap energy values. The comparison of the energy levels locations of the electrodeposited poly(naphthalenediimide-quaterthiophene) derivative (e-PNDIT4) and P3HT thin films transferred by the Inverse Langmuir-Schaefer (ILS) technique, demonstrates that e-PNDIT4 behaves as acceptor at the interface with P3HT. Steady state fluorescence studies have been performed in order to study the electron transfer in both planar (double layer) and bulk heterojunctions made of e-PNDIT4 and P3HT. The bulk heterojunction - obtained by thermal annealing of the double layer system - has shown a fluorescence quenching of about 97%, indicating an efficient electron transfer from the excited P3HT to e-PNDIT4. Furthermore, electrochromic properties of e-PNDIT4 thin films have been studied by means of spectroelectrochemical measurements. Transmittance versus time plots, recorded under an applied square wave potential, showed an optical contrast of about 20%. These studies open new possibilities in terms of all-polymer devices including the employment of a new class of symmetric push-pull derivatives and the development of fabrication processes exploiting the synergetic use of electrochemical and layer-by-layer deposition methods.