High-Speed Photothermal Patterning of Doped Polymer Films

Abstract

Organic semiconductors (OSCs) offer a new avenue to the next-generation electronics, but the lack of a scalable and inexpensive nanoscale patterning/deposition technique still limits their use in electronic applications. Recently, a new lithographic etching technique has been introduced that uses molecular dopants to reduce semiconducting polymer solubility in solvents and a direct-write laser to remove dopants locally, enabling rapid OSC etching with diffraction limited resolution. Previous publications postulated that the reaction that enables patterning is a photochemical reaction between photoexcited dopants with neutral solvent molecules. In this work, we analyze the photoinduced dissolution kinetics of F4TCNQ doped P3HT films using time-resolved in situ optical probing. We find two competing mechanisms that control de-doping and dissolution: the first is the photochemical reaction posited in the literature, and the second involves direct heating of the polymer by the laser, inducing increased solubility for both the polymer and dopant. We show that the wavelength-specific photochemical effect is dominant in low photon doses while the photothermal effect is dominant with high excitation rates regardless of laser wavelength. With sufficiently high optical intensity input, the photothermal mechanism can in principle achieve a high writing speed up to 1 m/s. Our findings bring new insights into the mechanisms behind laser direct writing of OSCs based on dopant induced solubility control and enable ultraprecise fabrications of various device configurations in large-scale manufacturing.

Reversible Doping and Photo Patterning of Polymer Nanowires

“…By comparison, DISC photopatterning uses polymer “out of the bottle” and can be adapted to pattern both doped and intrinsic polymers. [ 36 ] Several publications have now demonstrated diffraction limited patterning with a variety of form factors. Comparing all of the techniques, only DISC photopatterning and electrohydrodynamic organic nanowire printing [ 22 ] were able to achieve reliable wire/circuit fabrication to the diffraction limit of ≈300 nm using non‐chemically altered OSCs.…”

“…Our fastest recorded dissolution times are ≈1 μs per pixel, which is near the limit of mass transport by a fluid over the appropriate volume. [ 36 ] Figure 2e depicts the geometry of the doping and dedoping steps. Figure 2f shows a schematic of the photopatterning geometry that enables conductivity measurements of a single nanowire.…”

Super-Resolution Photothermal Patterning in Conductive Polymers Enabled by Thermally Activated Solubility

“…This conclusion is consistent with recent work by Su et al, who found that at low to moderate light intensities (<10 kW/cm 2 ) dissolution at 405 nm was dominated by photodedoping. 30 However, since the form of the rate law is identical with or without the reaction present, it appears that the resolution of the process is entirely controlled by the thermal dedoping step shown in Figure 1.…”

Foundry-compatible high-resolution patterning of vertically phase-separated semiconducting films for ultraflexible organic electronics

“…To minimize electronic device feature sizes, eliminate crosstalk in circuitry, and scale-up soft matter opto-electronic device fabrication, foundry-compatible patterning of all functional layers is essential for creating multiple circuitry layers, and systems integration 1 – 6 . Specifically, high-resolution patterning of robust semiconductor films in thin-film transistor (TFT) arrays must optimize the charge transport and on-current/off-current ratio ( I on : I off ) ratio, while achieving reliable deposition by solution-processing of all additional non-TFT components, including the gate dielectric/gate contact in top-gated TFTs, and the source-drain electrodes in top-contact TFTs, as well as planarization/passivation layers in both architectures 7 – 12 . Several pioneering studies realized patternable photo­crosslinked polymer semiconductors by appending crosslinkable moieties to the polymer backbone.…”