Solvent-Assistant Room Temperature Nanoimprinting-Induced Molecular Orientation in Poly(3-hexylthiophene) Nanopillars

Abstract

Nanoimprinting has been well explored to create nanostructures and to induce molecular orientation in conjugated polymer thin films. We demonstrate here that large area poly(3-hexylthiophene) (P3HT) nanopillar arrays can be fabricated by a simple, cost-effective nanoimprinting method in a solvent-swollen plasticized state at room temperature. In addition, the solvent-assistant room-temperature nanoimprinting induces face-on chain alignment in the P3HT nanopillars; i.e., the π–π stacking of P3HT is aligned normal to the substrate, favorable for organic photovoltaic cell applications. The face-on chain alignment solely depends on the diameters of nanopores defined in the nanoimprinting mold, rather than on the initial chain orientation in unprocessed thin films. Furthermore, a critical dimension of ca. 85 nm in diameter is found to be essentially needed to induce the face-on chain alignment within the nanopillars.

Quantitative analysis of the size effect of room temperature nanoimprinted P3HT nanopillar arrays on the photovoltaic performance

“…In our previous study, we have demonstrated that the SART-NIL method can be used not only to fabricate P3HT nanopillar arrays with varied diameters, but also to induce preferential molecular orientation in P3HT nanopillar arrays 30 at room temperature. In order to reveal the molecular orientation in P3HT nanopillar arrays after deposition of PCBM (OBHJ) and the size effect of P3HT nanopillar arrays on the molecular orientation, 2D-GIWAXD experiments were performed and the corresponding images are presented in Fig.…”

Recent Advances in Morphology Optimization for Organic Photovoltaics

“…Ordered heterojunction solar cell devices fabricated with the P3HT nanorod arrays had a PCE ≈2.4% . As the diameter of the P3HT nanorods is decreased, the proportion of P3HT chains in the face‐on orientation with respect to the substrate plane increases and the conductivity along the axis of the nanorods increases . These ordered heterojunction devices have lower energetic disorder and a lower density of trap states than conventional BHJ or planar heterojunction devices, and therefore exhibit less charge recombination loss .…”

Nanoimprint Lithography: Toward Functional Photonic Crystals

“…NIL can control chain alignment orientation in conjugated crystalline [122,125,126] and low molecular weight [127] polymers. It has been demonstrated that energetic stabilization [128], nano-confinement [129,130], and surface interaction with the mold [42] lead to preferential chain orientation with high charge mobility, increasing the solar cell performance [123]. Table 2 summarizes the data presented so far.…”