Molecular weight dependence of the morphology in P3HT:PCBM solar cells.

In polymer-based photovoltaic devices, optimizing and controlling the active layer morphology is important to enhancing the device efficiency. Using poly(3-hexylthiophene) (P3HT) with well-defined molecular weights (MWs), synthesized by the Grignard metathesis (GRIM) method, we show that the morphology of the photovoltaic active layer and the absorption and crystal structure of P3HT are dependent on the MW. Differential scanning calorimetry showed that the crystallinity of P3HT reached a maximum for intermediate MWs.

An in situ grazing incidence X-ray scattering study of block copolymer thin films during solvent vapor annealing.

In situ grazing-incidence small-angle X-ray scattering experiments on thin films of block copolymers during annealing in neutral solvent vapors are reported. By removing the solvent in a controlled manner, the period of the microphase separated morphology is found to increase with increasing block copolymer concentration in a power law manner with an exponent ∼ 2/3. By venting the systems at different rates during the solvent removal process, kinetically arresting the system, the period of the microphase separated morphology in the dried film can be varied.

Photocleavable Triblock Copolymers Featuring an Activated Ester Middle Block: "One-Step" Synthesis and Application as Locally Reactive Nanoporous Thin Films.

Polystyrene--poly(maleimide pentafluorophenyl ester--styrene)--poly(ethylene oxide) with an -nitrobenzyl ester junction was synthesized by "one-step" RAFT polymerization. Highly ordered and locally reactive nanoporous thin films were obtained from the photocleavable triblock copolymer after spin coating, solvent annealing, UV exposure, and washing with methanol/water to remove the minor block PEO. The local reactivity in the thin films was demonstrated by fabrication of iron oxide nanotori after post-modification with an amino-functionalized ferrocene and treatment with oxygen plasma.

On the self-assembly of brush block copolymers in thin films.

We describe a simple route to fabricate two dimensionally well-ordered, periodic nanopatterns using the self-assembly of brush block copolymers (brush BCPs). Well-developed lamellar microdomains oriented perpendicular to the substrate are achieved, without modification of the underlying substrates, and structures with feature sizes greater than 200 nm are generated due to the reduced degree of chain entanglements of brush BCPs. A near-perfect linear scaling law was found for the period, L, as a function of backbone degree of polymerization (DP) for two series of brush BCPs.

Line patterns from cylinder-forming photocleavable block copolymers.

A robust route for the preparation of nanoscopic line patterns from polystyrene-block-poly(ethylene oxide) featuring a photocleavable o-nitrobenzyl ester junction is demonstrated. After mild UV (λ = 365 nm) exposure and selective removal of the PEO microdomains, the polymer trench patterns are used as scaffold to fabricate highly ordered arrays of silica or Au line patterns.

Solvent-assisted directed self-assembly of spherical microdomain block copolymers to high areal density arrays.

The fabrication process for 5 Tb/in(2) bit patterns using solvent-assisted directed self-assembly is investigated. The N-methyl-2-pyrrolidone solvent vapor-annealing method was used to achieve good long-range lateral ordering of low-molecular-weight polystyrene-block-polydimethylsiloxane with a lattice spacing of 11 nm on flat Si substrates, PS modified substrates and lithographically patterned substrates, respectively.

Self-assembly of symmetric brush diblock copolymers.

Self-assembled structures of brush block copolymers (BrBCPs) with polylactide (PLA) and polystyrene (PS) side chains were studied. The polynorbornene-backbone-based BrBCPs containing approximately equal volume fractions of each block self-assembled into highly ordered lamellae with domain spacing ranging from 20 to 240 nm by varying molecular weight of the backbone in the bulk state, as revealed by small-angle X-ray scattering (SAXS). The domain size increased approximately linearly with backbone length, which indicated an extended conformation of the backbone in the ordered state.

Orienting block copolymer microdomains with block copolymer brushes.

A simple, rapid, and robust technique for controlling the self-assembly of block copolymers (BCPs) with a large segmental interaction parameter, χ, is described using a surface modified with anchored BCP brushes. End-functionalized poly(styrene-b-ethylene oxide)s (PS-b-PEOs), where the fraction of PS (f(PS)) was varied, end-functionalized neat PS, and end-functionalized neat PEO were end-grafted onto Si substrates modifying the surface with polymer brushes. Thin films of cylinder-forming PS-b-PEO were prepared on modified Si substrates and thermally annealed.

Fabrication of silicon oxide nanodots with an areal density beyond 1 teradots inch(-2).

The combination of solvent annealing, surface reconstruction, and a tone-reversal etching procedure provides an attractive approach to utilize block copolymer (BCP) lithography to fabricate highly ordered and densely packed silicon oxide nano-dots on a surface. The obtained silicon oxide nano-dots feature an areal density of 1.3 teradots inch(-2) .

Highly ordered nanoporous template from triblock copolymer.

Silica nanoporous templates from poly(1,4-isoprene)-block-polystyrene-block-poly(2-vinyl pyridine) (IS2VP) were prepared. The films of IS2VP spin-coated from toluene showed a dimple-type structure with short-range lateral order. When the films were exposed to a mixed solvent vapor of toluene/hexane, a highly ordered and oriented core-shell structure, consisting of an outer shell of PI, a middle shell of PS, and a core of P2VP, was obtained.