Research ArticleMATERIALS SCIENCE

Programmable and coherent crystallization of semiconductors

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Science Advances  03 Mar 2017:
Vol. 3, no. 3, e1602462
DOI: 10.1126/sciadv.1602462
  • Fig. 1 Crystallization in amorphous films tends to be initiated in thicker regions through homogeneous nucleation.

    (A) Optical micrographs of TES ADT films during solvent vapor annealing. The leftmost figure shows the height profile (see fig. S1). (B and C) Polarized optical micrographs of a vacuum-deposited rubrene film with a deliberate thickness step (yellow dashed line) after thermal annealing for only ~10 s (B) and thicker ribbons fully crystallized (while thin sections remain amorphous) after ~60 s (C). (D) Plots of the estimated nucleation starting time at different temperatures (top) for MoOx films (□) of different thicknesses. The line fits at the bottom have a fixed slope of −1. Evaporated rubrene thin films (○) were annealed at T = 150°C. Evaporated MoOx thin films were annealed at T = 280°C (□) and T = 300°C (■). Spin-coated TES ADT thin films (Δ) were crystallized by solvent vapor annealing. The onset of nucleation was identified visually for all samples by inspection using polarized optical microscopy (see fig. S4).

  • Fig. 2 Programming crystallization and producing bespoke microstructures by manipulating thin-film topography.

    (A and B) Schematics representing a two-step vacuum deposition method in which a shadow mask creates a thicker region of arbitrary pattern (for example, rectangular strips) on a uniform film to subsequently pattern and seed the crystallization coherently. (C) Polarized optical micrograph of thermally annealed rubrene films using the two-step deposition method for ~60 s (200 nm for the top left brighter part and 40 nm for the dimmer part). (D and E) Schematics representing the mechanical patterning method, which uses a solid object to stamp or to scratch the film with the aim of creating thickness variations at designated locations. (F and G) Polarized optical micrograph of crystallized TES ADT samples with periodically imprinted lines (F) and dots (G). The imprint lines/dots seed the linear/spherulitic crystallization. (H) Polarized optical micrographs of a rubrene film with the same thickness contrast as (C) but with more sophisticated patterns. (I) Polarized optical micrograph of solvent vapor annealed of a TES ADT thin film with various grid-like patterns. (J to M) Polarized optical micrographs of amorphous thin films crystallized using imprinted lines, including vacuum-deposited rubrene (J), vacuum-deposited MoOx (K), solution-processed PEO (L), and solution-processed PbI2 hybrid perovskite DMF solvate film (M).

  • Fig. 3 Improved microstructural homogeneity by linear patterning of thin-film crystallization.

    (A) Schematic illustration of a bottom-gate top-contact OTFT device. (B and C) Polarized optical micrographs of an OTFT using a conventionally crystallized TES ADT film (α) (B) and an OTFT using a periodic linear crystallization of TES ADT (αp) (C). (D) μGIWAXS maps focusing on the Q value of the (011) reflection at the x-axis of the detector (Qx) of TES ADT in the area associated with the polarized micrograph. (E) Absorption spectra of TES ADT films in γ, α, and αp phases and microstructures, as measured by PDS. Inset to (E) plots the Urbach energy extracted from the exponential tail of the absorption spectra.

  • Fig. 4 Improved OTFT device performance reproducibility by linear patterning of thin-film microstructure with respect to OTFT channel.

    (A) Close-up view of the channel of OTFTs with respect to the distance (d) of the linear crystallization seed line (indicated by the top yellow line). Hole mobility (saturation) of OTFT devices with respect to d. The insets in the bottom panel of (A) show a representative (011) reflection for d < 120 μm (□) and d > 120 μm (□). (B) Hole mobility and its distribution over >10 devices prepared using different scenarios. The filled circles represent the maximum and minimum values, whereas the boxes represent 20, 50, and 75% of the values. Insets to (B) show polarized optical micrographs of TES ADT thin films in various microstructural states in the channel area of the OTFT devices. (C) Four representative transfer characteristics in the saturation regime of OTFT devices prepared following each scenario.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1602462/DC1

    fig. S1. Height profile of the solidified droplet of TES ADT.

    fig. S2. Polarized optical micrographs of MoOx thin films with different thicknesses.

    fig. S3. Illustrative plots of the volumetric and areal nucleation rates with respect to temperature.

    fig. S4. Polarized optical micrographs of MoOx thin films (100 nm) at different annealing times.

    fig. S5. QCM-D measurements during solvent vapor annealing.

    fig. S6. Atomic force microscopy topography image of a TES ADT film scratched with a needle.

    fig. S7. Optical micrographs of TES ADT and PCBM films crystallized using linear seeding.

    fig. S8. μGIWAXS images of the αp and α phases.

    fig. S9. Typical OTFT output characteristics of TES ADT thin films using conventional and programmable crystallization.

    movie S1. Conventional crystallization of a TES ADT film proceeding stochastically and incoherently.

    movie S2. Linear programmed crystallization of TES ADT proceeding simultaneously and coherently from horizontal seeding lines.

    movie S3. Periodic dot array crystallization of TES ADT proceeding simultaneously and coherently from an array of imprinted seed dots.

    movie S4. Square programmed crystallization of TES ADT proceeding simultaneously and coherently from horizontal and vertical seeding lines.

    movie S5. Square and rectangular programmed crystallization of TES ADT proceeding simultaneously and coherently from horizontal and vertical seeding lines.

    References (41, 42)

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Height profile of the solidified droplet of TES ADT.
    • fig. S2. Polarized optical micrographs of MoOx thin films with different thicknesses.
    • fig. S3. Illustrative plots of the volumetric and areal nucleation rates with respect to temperature.
    • fig. S4. Polarized optical micrographs of MoOx thin films (100 nm) at different annealing times.
    • fig. S5. QCM-D measurements during solvent vapor annealing.
    • fig. S6. Atomic force microscopy topography image of a TES ADT film scratched with a needle.
    • fig. S7. Optical micrographs of TES ADT and PCBM films crystallized using linear seeding.
    • fig. S8. μGIWAXS images of the αp and α phases.
    • fig. S9. Typical OTFT output characteristics of TES ADT thin films using conventional and programmable crystallization.
    • Legends for movies S1 to S5
    • References (41, 42)

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    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (format). Conventional crystallization of a TES ADT film proceeding stochastically and incoherently.
    • movie S2 (format). Linear programmed crystallization of TES ADT proceeding simultaneously and coherently from horizontal seeding lines.
    • movie S3 (format). Periodic dot array crystallization of TES ADT proceeding simultaneously and coherently from an array of imprinted seed dots.
    • movie S4 (format). Square programmed crystallization of TES ADT proceeding simultaneously and coherently from horizontal and vertical seeding lines.
    • movie S5 (format). Square and rectangular programmed crystallization of TES ADT proceeding simultaneously and coherently from horizontal and vertical seeding lines.

    Download Movies S1 to S5

    Files in this Data Supplement: