book of abstracts - IM2NP

A B S T R A C T S FRIDAY, JULY 2 N A N O S E A 2 0 1 0
Room Port-Pin
9H00-9H30
Improving photovoltaic response of CNTs/Si heterojunctions using different
carbon nanotubes types and CNTs film thicknesses.
P. Castrucci1, S. Del Gobbo1, L. Camilli1, M. Scarselli1, S. Casciardi2, F.
Tombolini2, M. De Crescenzi1 (1Dipartimento di Fisica and Unità CNISM, Università di Roma Tor
Vergata Via della Ricerca Scientifica 1, I-00133 Roma, Italy; 2 Dipartimento di Igiene del Lavoro, ISPESL, I-00040
Monte Porzio Catone, Italy). paola.castrucci@roma2.infn.it, silvano.delgobbo@roma2.infn.it,
manuela.scarselli@roma2.infn.it, luca.camilli@roma2.infn.it, maurizio.decrescenzi@roma2.infn.it,
stefano.casciardi@ispesl.it , francesca.tombolini@ispesl.it
1 – Introduction
In the last years, carbon nanotubes (CNTs) have been considered a great promise in the development of highefficiency
solar cells, due to their excellent transport and electronic properties. Use of nanotubes in this area
has been primarily focussed on hybrid structures based on conjugated polymers giving rise to cells
characterized by modest efficiency and low environmental stability. 1,2 Recently the investigation of the
CNTs/silicon heterostructure paved the way for developing solar cells with moderate efficiency, good
stability and reduced cost, by integrating nano- and silicon technologies. 3-5 Nanotubes dispersed or grown
on silicon substrate are fundamental for separation, transport and collection of charges which have been
mostly generated in the silicon underneath. In this scenario, the thickness of the nanotubes film is a crucial
point to improve the efficiency of the solar cell as well as the number of the walls forming the CNTs.
2 – Abstract
In this work, we report recent studies on the efficiency of CNTs/silicon heterojunctions pointing our
attention on CNTs film thickness and nanotubes nature. We grew nanotubes directly on the silicon substrate
by chemical vapour deposition in acetylene atmosphere at T = 780 °C. Iron catalyst has been pre-deposited
on the bare Si surface at room temperature. A set of samples has been obtained by varying the nominal
thickness of the iron catalyst. We found that the structure of the grown tubes and to the morphology of the
CNTs film is directly connected to the dimension of the catalyst nanoparticles. Incident photon conversion
efficiency (IPCE) and power conversion efficiency have been measured by electrically contacting the
nanotubes film with silver paint and using an optical set-up made of a Xenon lamp equipped with a
monochromator, focusing and collecting optics and a) a reflecting light chopper and lock-in amplifier and b)
a Keithley 2602A sourcemeter, respectively. Scanning electron microscopy and transmission electronic
microscopy have been performed to measure the thickness of the nanotubes film and the CNTs size. We
observed that there exists an optimal thickness of the nanotubes film, for which nanotubes film behaves as an
almost transparent electrode for silicon illumination and at the same time forms the highest number of
heterojunctions to separate and transport charges. On the other hand, the number of CNT walls contributes to
establish the metallic or semiconducting character of the film and its work function, so contributing to the
intensity of the collected photocurrent. In best case, we obtained an IPCE of 9% for a catalyst iron thickness
of 0.1nm.
3 – Conclusion
In conclusion we report a study on the connection between the nominal thickness of the iron catalyst film
deposited to grow carbon nanotubes and (i) their diameter and number of walls, (ii) the morphology and
131