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

Abstract

We develop a solvent-assisted room temperature nanoimprint lithography (SART-NIL) technique to fabricate an ideal active layer consisting of poly(3-hexylthiophene) nanopillar arrays surrounded by [6,6]-phenyl-C61-butyric acid methyl ester. Characterization by scanning electron microscopy, two-dimensional grazing incidence wide angle X-rays diffraction, and conducting atomic force microscopy reveals that the SART-NIL technique can precisely control the size of P3HT nanopillar arrays. With the decrease in diameters of P3HT nanopillar arrays, the P3HT nanopillar arrays exhibit a more preferable face-on molecular orientation, enhanced UV-vis absorption and higher conducting ability along the direction perpendicular to the substrate. The ordered bulk heterojunction film consisting of P3HT nanopillar arrays with a diameter of ∼45 nm (OBHJ-45) gives face-on orientation, a high interfacial area of 2.87, a high conducting ability of ∼130 pA and efficient exciton diffusion and dissociation. The polymer solar cell (PSC) based on an OBHJ-45 film exhibits a significantly improved device performance compared with those of PSCs based on the P3HT nanoapillar arrays with diameters ∼100 nm and ∼60 nm. We believe that the SART-NIL technique is a powerful tool for fabricating an ideal active layer for high performance PSCs.

Controlled Mutual Diffusion between Fullerene and Conjugated Polymer Nanopillars in Ordered Heterojunction Solar Cells

“…Typically, cSFM requires contact mode operation. However, the contact mode operation on soft samples can lead to surface deformation, such that fragile polymer nanopillar structures can be easily bent or even destroyed . To reduce or minimize this deleterious effect, a new cSFM mode has recently been developed, which is based on the torsion mode and/or on the peak force.…”

“…The molecular orientation as well as domain size could be tailored with different kinds of templates and surface treatments. Silicon molds and anodized aluminum oxide (AAO) templates have typically been employed to realize nanopillars with diameters ranging from 20 to 250 nm. Several studies have shown that the power conversion efficiency increases when the donor–acceptor distance approaches the exciton diffusion length .…”

“…Silicon molds and anodized aluminum oxide (AAO) templates have typically been employed to realize nanopillars with diameters ranging from 20 to 250 nm. Several studies have shown that the power conversion efficiency increases when the donor–acceptor distance approaches the exciton diffusion length . In addition, it has been demonstrated that the orientation of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) donor molecules could change from the edge‐on to the face‐on on substrates when they are confined within nanostructure .…”

“…In addition, it has been demonstrated that the orientation of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) donor molecules could change from the edge‐on to the face‐on on substrates when they are confined within nanostructure . The face‐on orientation, whose π–π stacking is perpendicular to substrate, leads to one or two orders of magnitude higher carrier mobility than the edge‐on orientation in the direction vertical to electrodes and it is thus beneficial for the charge extraction in organic solar cells . However, it is still difficult to precisely control the domain size of donor and acceptor materials using NIL because it requires different diameters and heights of templates for every different nanostructure.…”

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 .…”