Research ArticleAPPLIED SCIENCES AND ENGINEERING

Tuning, optimization, and perovskite solar cell device integration of ultrathin poly(3,4-ethylene dioxythiophene) films via a single-step all-dry process

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Science Advances  22 Nov 2019:
Vol. 5, no. 11, eaay0414
DOI: 10.1126/sciadv.aay0414
  • Fig. 1 Schematic illustration of PEDOT synthesis by the oCVD method.

    (A) The postdeposition acidic rinsing step (e.g., MeOH or HBr rinsing) is generally used for poly(3,4-ethylene dioxythiophene) (PEDOT) films grown using FeCl3 as an oxidant to remove unreacted oxidants and oxidation by-products and increasing conductivity. (B) Synthesizing PEDOT using VOCl3 as an oxidant does not require the acidic rinsing treatment, and the fabricated film is directly used in device fabrication as a true single-step, all-dry process.

  • Fig. 2 Different crystallization orientation induced by process parameters.

    (A) The out-of-plane GIXRD θ − 2θ diffraction patterns of as-deposited PEDOT films grown on silicon substrates at the different deposition temperature of 110° and 140°C with varying VOCl3 saturation ratio. a.u., arbitrary units. Schematic illustration of crystallization orientation and the distance between planes in (B) face-on orientation and (C) edge-on orientation. (D) Summary of the percentage of preferential crystallization orientation in the bar chart for all 16 PEDOT films grown at different deposition temperature and VOCl3 saturation ratio. The percentage of preferential orientation was calculated on the basis of the normalized integrated peak intensities after applying the Lorentz polarization (LP) factor. The lengths of the red-colored and blue-colored bars display the percentage of the face-on and edge-on orientation, respectively. (E) The percentage of preferential crystallization orientation in PEDOT films grown at the deposition temperature of 150°C and using FeCl3 as an oxidant as a comparison with the volatile liquid oxidant (VOCl3) that is used in this study.

  • Fig. 3 Effect of PEDOT lattice parameter on electrical conductivity.

    (A) b-axis lattice parameter as a function of OSR in PEDOT films grown at the different deposition temperature of 110° and 140°C. (B) The relation of electrical conductivity and b-axis lattice parameter of PEDOT films grown at the different deposition temperature. (C) Schematic illustrations of possible current transport direction in the pure face-on orientation with low-angle grain boundaries. (D) Illustration of the high impact of low b-axis lattice parameter (short π-π stacking distance) and chain bridging to avoid localization in the pure face-on microstructure. The blue arrows display the direction of current flow. (E) Schematic illustration of b-axis lattice parameter influence on the intra- and interchain charge transport. The intrachain charge transfer was affected by the doping level, while the interchain charge transfer was influenced by the charge transfer integral. (F) Left: The cross-sectional scanning electron microscopy (SEM) image of the oCVD PEDOT film grown by VOCl3 as an oxidant with a thickness of ~80 nm on a silicon wafer with etched trench structures demonstrating high conformality of the deposition. Right: The cross-sectional SEM image of the highly conformal oCVD PEDOT film on a trench with high magnification.

  • Fig. 4 The optical characteristics of PEDOT films.

    (A) Image of deposited PEDOT films on blank microscope glass slides (thickness of 1 mm) at different OSR. (B) The optical transmittance of PEDOT films grown at the deposition temperature of 140°C and different VOCl3 saturation ratio in the visible regime ranging from 300 to 800 nm. (C) The FoM (FoM = σdcop, where σdc and σop are dc conductivity and optical conductivity, respectively) as a function of OSR in PEDOT films grown at the deposition temperature of 140°C. The blue and green dashed lines are the highest reported σdcop values in oCVD PEDOT films grown by FeCl3 as an oxidant after acidic rinsing treatment and the benchmark indicator of the commercial viability of transparent conductors, respectively. (D) The optical bandgap and the Urbach energy values as a function of OSR for PEDOT films grown at the deposition temperature of 140°C.

  • Fig. 5 PV characterization of PSC devices with oCVD PEDOT and PEDOT:PSS.

    (A) Cross-sectional SEM image and (B) schematic illustration of the device architecture for PSC device based on oCVD PEDOT HTL. (C) J-V curves and (D) EQE spectra and integrated current density of the PSCs fabricated on oCVD PEDOT and PEDOT:PSS HTLs. (E) The shelf-life stability performance of inverted PSCs with oCVD PEDOT and PEDOT:PSS HTLs. Notably, unencapsulated devices were kept in ambient air with 20% relative humidity, and the PCE was measured every 3 days.

  • Table 1 PV parameters of the best-performing PSCs with oCVD PEDOT and PEDOT:PSS HTLs.

    The PV features [open circuit voltage (VOC), short circuit current density (JSC), fill factor (FF), PCE, and JSC estimated from EQE] of PSCs based on oCVD PEDOT and PEDOT:PSS HTLs.

    Voc (V)Jsc (mA/cm2)FF (%)PCE (%)Jsc from EQE
    oCVD PEDOT0.9624.107818.0423.05
    PEDOT:PSS0.9423.247416.2021.60

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/11/eaay0414/DC1

    Section S1. Methods and materials characterization

    Section S2. Normalized integrated intensity based on LP factor, investigation of crystallite size, and lattice parameter

    Section S3. Hopping probability by Miller-Abrahams model

    Section S4. Optical bandgap (Eg) and Urbach energy (EU) investigation

    Table S1. The deposition parameters used in the growth of oCVD PEDOT films.

    Table S2. The normalized integrated peak intensity of oCVD PEDOT films.

    Table S3. The XPS elemental analysis of PEDOT films.

    Table S4. The crystallite domain size in PEDOT films.

    Table S5. The a-axis and b-axis lattice parameter information of PEDOT films.

    Fig. S1. Saturation vapor pressure of monomer and oxidant at different temperatures.

    Fig. S2. Thickness and deposition rate of PEDOT films as a function of process parameters.

    Fig. S3. Effect of process parameters on the crystalline orientation of PEDOT films.

    Fig. S4. The XPS analysis of PEDOT films.

    Fig. S5. The effect of OSR on the a-axis lattice parameter of PEDOT films.

    Fig. S6. The optical absorption spectra of PEDOT films.

    Fig. S7. Urbach plot for PEDOT films.

    Fig. S8. Statistics of the PV parameters for the PSCs with different HTLs.

    Fig. S9. Statistics of HIs for the PSC devices.

    Fig. S10. Variation of PSC device performance versus the thickness of oCVD PEDOT.

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Methods and materials characterization
    • Section S2. Normalized integrated intensity based on LP factor, investigation of crystallite size, and lattice parameter
    • Section S3. Hopping probability by Miller-Abrahams model
    • Section S4. Optical bandgap (Eg) and Urbach energy (EU) investigation
    • Table S1. The deposition parameters used in the growth of oCVD PEDOT films.
    • Table S2. The normalized integrated peak intensity of oCVD PEDOT films.
    • Table S3. The XPS elemental analysis of PEDOT films.
    • Table S4. The crystallite domain size in PEDOT films.
    • Table S5. The a-axis and b-axis lattice parameter information of PEDOT films.
    • Fig. S1. Saturation vapor pressure of monomer and oxidant at different temperatures.
    • Fig. S2. Thickness and deposition rate of PEDOT films as a function of process parameters.
    • Fig. S3. Effect of process parameters on the crystalline orientation of PEDOT films.
    • Fig. S4. The XPS analysis of PEDOT films.
    • Fig. S5. The effect of OSR on the a-axis lattice parameter of PEDOT films.
    • Fig. S6. The optical absorption spectra of PEDOT films.
    • Fig. S7. Urbach plot for PEDOT films.
    • Fig. S8. Statistics of the PV parameters for the PSCs with different HTLs.
    • Fig. S9. Statistics of HIs for the PSC devices.
    • Fig. S10. Variation of PSC device performance versus the thickness of oCVD PEDOT.

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