posted on 2020-03-10, 19:13authored byDomenikos Chryssikos, Markus Wiesinger, Oliver Bienek, Hartmut Wiggers, Martin Stutzmann, Anna Cattani-Scholz, Rui N. Pereira
Thin
films of crystalline silicon nanoparticles (Si NPs) processed
from liquid dispersions of NPs (NP inks) using printing-type deposition
methods are currently being intensively investigated for the development
of electronic and optoelectronic nanotechnologies. Various (opto)electronic
applications have already been demonstrated based on these materials,
but so far, devices exhibit modest performance because of relatively
low electrical conductivity and charge carrier mobility. In this work,
we aim at unveiling the major factors affecting the long-range transport
of charges in Si NP thin films. For this, we monitor the electrical
properties of thin-film field effect transistors (FETs) as the active
channel of the devices is gradually filled with Si NPs. To produce
these FET devices featuring stable, sparse Si NP networks within the
active channel, we developed a fabrication protocol based on NP deposition
by device substrate immersion in a NP ink, made of Si NPs and chlorobenzene,
followed by annealing and ultrasonication. We found that both the
electrical conductivity and the charge carrier mobility of the FETs
increase extremely rapidly as the device channel coverage with NPs
increases. Thus, the NP network corresponds effectively to an inhomogeneous
blend of conducting and insulating Si NPs, with the most efficient
charge percolation paths involving only a fraction of the NPs. We
discuss the factors that may lead to this behavior, in view of developing
Si NP thin films with competitive charge transport characteristics.