2 research outputs found
Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates
We
demonstrate that local and long-range orders of polyÂ(3-hexylthiophene)
(P3HT) semicrystalline films can be synergistically improved by combining
chemical functionalization of the substrate with solution-state disentanglement
and preaggregation of P3HT in a θ solvent, leading to a very
significant enhancement of the field effect carrier mobility. The
preaggregation and surface functionalization effects combine to enhance
the carrier mobility nearly 100-fold as compared with standard film
preparation by spin-coating, and nearly 10-fold increase over the
benefits of preaggregation alone. In situ quartz crystal microbalance
with dissipation (QCM-D) experiments reveal enhanced deposition of
preaggregates on surfaces modified with an alkyl-terminated self-assembled
monolayer (SAM) in comparison to unaggregated polymer chains in the
same conditions. Additional measurements reveal the combined preaggregation
and surface functionalization significantly enhances local order of
the conjugated polymer through planarization and extension of the
conjugated backbone of the polymer which clearly translate to significant
improvements of carrier transport at the semiconductor–dielectric
interface in organic thin film transistors. This study points to opportunities
in combining complementary routes, such as well-known preaggregation
with substrate chemical functionalization, to enhance the polymer
self-assembly and improve its interfacial order with benefits for
transport properties
Solvent Vapor Annealing in the Molecular Regime Drastically Improves Carrier Transport in Small-Molecule Thin-Film Transistors
We demonstrate a new way to investigate and control the
solvent vapor annealing of solution-cast organic semiconductor thin
films. Solvent vapor annealing of spin-cast films of 6,13-bisÂ(triisopropylsilylethynyl)
pentacene (TIPS-Pn) is investigated in situ using quartz crystal microbalance
with dissipation (QCM-D) capability, allowing us to monitor both solvent
mass uptake and changes in the mechanical rigidity of the film. Using
time-resolved grazing incidence wide angle X-ray scattering (GIWAXS)
and complementary static atomic force microscopy (AFM), we demonstrate
that solvent vapor annealing in the molecular regime can cause significant
performance improvements in organic thin film transistors (OTFTs),
whereas allowing the solvent to percolate and form a liquid phase
results in catastrophic reorganization and dewetting of the film,
making the process counterproductive. Using these lessons we devise
processing conditions which prevent percolation of the adsorbed solvent
vapor molecules for extended periods, thus extending the benefits
of solvent vapor annealing and improving carrier mobility by nearly
two orders of magnitude. Ultimately, it is demonstrated that QCM-D
is a very powerful sensor of the state of the adsorbed solvent as
well as the thin film, thus making it suitable for process development
as well as in-line process monitoring both in laboratory and in future
manufacturing settings