Optically transparent semiconducting polymer nanonetwork for flexible and transparent electronics
Kilho Yua,b,c,1, Byoungwook Parka,b,c,1, Geunjin Kimb,c, Chang-Hyun Kima,c, Sungjun Parka, Jehan Kimd, Suhyun Junga,b,c, Soyeong Jeonga,b,c, Sooncheol Kwonb,c, Hongkyu Kangb,c, Junghwan Kimb,c, Myung-Han Yoona, Kwanghee Leea,b,c,2 a
Department of Nanobio Materials and Electronics, School of Materials Science and Engineering,
Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea; bHeeger Center for Advanced Materials, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea; cResearch Institute for Solar and Sustainable Energies, Gwangju Institute of Science and Technology, Gwangju 61005, Republic of Korea; dPohang Accelerator Laboratory, Pohang University of Science and Technology, Pohang 37673, Republic of Korea 1
These authors contributed equally to this work.
2
E-mail:
[email protected]
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I. Supplementary Methods PLED solutions for emissive layers. PDY-132 (Super Yellow, Merck) and MEH-PPV (Mr 425,000, Sigma-Aldrich) were dissolved in chlorobenzene at concentrations of 7 mg ml1 and 8 mg ml1, respectively. SPW-111 (Merck) and F8BT (Mr 35,000, American Dye Source) were separately dissolved in toluene at a concentration of 9 mg ml1.
Large-area FT-FET device fabrication. A solution of polydimethylsiloxane (PDMS, Sylgard 184 silicone elastomer, Dow Corning) mixed with a hardener (10:1 weight ratio) was spin cast onto a cleaned glass slide (10 cm 10 cm) at 5000 rpm for 20 s, and the film was subsequently annealed at 70 ºC for 1 h. A PEN (t 125 m) substrate was then adhered to the PDMS surface for the subsequent fabrication processes. The PEN substrate was cleaned via sequential ultrasonication in water, acetone, and isopropyl alcohol and treated with UV/ozone exposure for 3 min. For the bottom electrodes, PEDOT:PSS (CleviosTM P Jet 700, Heraeus) was directly patterned via an inkjet-printing method using a Dimatix Materials Printer (DMP2800 Series, Fujifilm USA). A DPP2T/PS (15/85 wt % ratio) solution was spin cast onto the substrate in an inert nitrogen atmosphere, and the film was annealed at room temperature for 3 minutes under low-vacuum conditions (102 Torr). To fabricate the gate insulating layer, we used poly(methyl methacrylate) (PMMA, Mr 120,000, Sigma-Aldrich). Note that we could not use CYTOP for the insulator because the subsequent inkjet patterning of the PEDOT:PSS for the gate electrode onto CYTOP would be impossible because of the very low surface energy of CYTOP. The PMMA (80 mg ml1) dissolved in n-butyl acetate was spin cast onto the semiconducting layer to a thickness of 500 nm, and the film was annealed at 80 ºC for 1 h. The measured capacitance of the PMMA was 6.0 nF cm2. Finally, the top2
gate electrode was also fabricated through inkjet printing the PEDOT:PSS. No annealing process was used for the bottom and top PEDOT:PSS contacts. The resulting device could be easily detached from the supporting substrate because of the PDMS.
FT-FET-LED integrated device fabrication. PDMS supports on glass substrates (10 cm 10 cm) were prepared as described for large-area FT-FET device fabrication. We attached a PEN/indium-tin-oxide (ITO) substrate to the PDMS surface for the subsequent fabrication processes. The PEN/ITO substrate was cleaned via sequential ultrasonication in water, acetone, and isopropyl alcohol and treated with UV/ozone exposure for 20 min. Then, a zinc oxide (ZnO) precursor solution (2.5 wt % zinc acetate dehydrate and 0.7 wt % ethanolamine in 2-propanol) was spin cast at 4000 rpm onto the ITO surface, and the film was then annealed at 130 ºC for 10 min. Subsequently, a polyethyleneimine (PEI) solution (0.05 wt % in 2-propanol) was spin cast at 5000 rpm onto the ZnO surface. The various light-emitting layers were spin coated from solution, and the films were subsequently thermally annealed at 70 ºC for 10 min under an inert nitrogen atmosphere. Then, 20-nm-thick MoOx was thermally deposited, and PEDOT:PSS (CleviosTM P AI4083, Heraeus) with 1 wt % fluorosurfactant (Capstone FS-31, DuPont) was spin coated at 1000 rpm and subsequently thermally annealed at 100 ºC for 10 min to improve hole injection and for FET fabrication there on. Thin Au (15 nm) semi-transparent source/drain electrodes were thermally deposited and patterned using shadow masks. Finally, charge-transport layers, gate insulators, and gate electrodes were fabricated identically to those of the TGBC FETs.
FET characterization. The I-V characteristics of the FETs were measured using a Keithley 3
4200 source meter. The saturation was calculated from the equation 2
𝜕√𝐼
μsat = ( 𝜕𝑉 DS) (2𝐿/𝑊𝐶i ), GS
and the linear was calculated as μlin =
𝜕𝐼DS 𝜕𝑉GS
1
∙𝑉
DS
(𝐿/𝑊𝐶i ),
where IDS is the drain-source current, VGS is the gate voltage, VDS is the drain-source voltage, Ci is the capacitance per unit area, and L and W are the channel length and width, respectively. The FETs were also characterized at various temperatures in a cryostat.
PLED characterization. The I-V-L characteristics of the FT-FET-PLEDs were measured using a PR650 spectrophotometer with two Keithley 2400 source meters.
TEM characterization. The samples were obtained by peeling the spin-cast films on glass substrates and transferring them onto 200-mesh copper grids (Electron Microscopy Sciences, USA). The TEM images were acquired using a Tecnai G2 F30 S-Twin microscope (FEI USA) operated at an acceleration voltage of 300 kV.
X-ray characterization. 2D GIWAXS images were acquired at the 3C-SAXSl beam line at the Pohang Accelerator Laboratory (PAL) using a monochromatic X-ray radiation source of 10.22 keV ( 1.213 Å ) and a 2D X-ray detector (Mar165 CCD). The samples were placed on a z-axis goniometer and were maintained under vacuum conditions (10-3 Torr) during irradiation.
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AFM characterization. The AFM instrument (XE-100, Park Systems) was operated in tapping mode for samples on glass substrates. To remove PS, we thoroughly rinsed the DPP2T/PS film with propylene glycol monomethyl ether acetate (PGMEA, Sigma-Aldrich) and dried it for several minutes under a nitrogen flow and low-vacuum conditions (102 Torr) before testing.
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II. Supplementary Notes Note S1. Structural analysis of DPP2T and DPP2T/PS based on optical absorption spectra. Optical absorption spectra can provide crucial information about chain aggregation (Fig. 1B). The absorption spectrum of the DPP2T solution, which shows spectral features characteristic of a polymer chain (1), is identical to that of the DPP2T/PS solution; thus, the conformation of DPP2T is not affected by the PS in the solution phase. Meanwhile, the DPP2T film presents a broadened absorption spectrum and an increased intensity ratio of the 0-1 transition (0-1 754 nm) over the 0-0 transition (0-0 832 nm), indicating dominant intermolecular stacking in the solid phase (2). By contrast, the spectral features of the DPP2T/PS film are similar to those of the solution phase, with only a slightly increased 0-1 transition, indicating that the interchain order is considerably suppressed compared with that of the pure DPP2T film.
Note S2. FET characteristics of the pure DPP2T films. DPP2T devices without PS but with DPP2T contents equal to those of the DPP2T/PS devices were also investigated to exclude the dependence on the DPP2T concentration and isolate the effect of PS blending at each blending condition (Fig. S11). The pure DPP2T devices show a moderate monotonically increase and saturation of as the concentration increases (because even the 100% DPP2T layer is very thin [t 10 nm], thinner films may exhibit morphological discontinuity and defects) (3).
Note S3. Measurements and modeling of T-dependent device characteristics. We referred to the theoretical framework utilized by Sirringhaus and colleagues (4, 5), which accounts for 6
the T- and gate voltage (VGS)-dependent drain-source current (IDS), and we modeled our data accordingly to describe the charge-transport mechanisms of the two systems (Fig. S16A). The transport theories dictate the saturation-regime IDS as a power-law function of VGS VT (where VT is the threshold voltage), with its characteristic exponent being converted into the energetic width of the density of states (DOS) (6-9) for localized states. In turn, IDS obeys a power law defined by the exponent , as follows: IDS VGS VT. The log-log representation of the data in Fig. S16B shows good linearity over a wide T range, enabling the unambiguous extraction of and reliable reproducibility of the measured device performances. In Fig. S16C, surprisingly low values approaching 2 with very low T dependence indicate that both systems are exceptionally resilient to pervasive disorder, which is consistent with the results obtained for other high- near-amorphous copolymer materials (5). Most importantly, the slope of versus 1/T reflects the degree of thermal accessibility of the localized sites, and the lower dependence observed in DPP2T/PS indicates a considerably reduced energetic disorder compared with that in pure DPP2T (see Fig. S17).
Note S4. Structural analysis of DPP2T/PS. According to the TEM images of DPP2T and DPP2T/PS films, the flexible PS matrix seems to prevent the entanglement of the rigid DPP2T chains by providing a more flexible surrounding environment. An additional structural analysis using atomic force microscopy (AFM) was performed, revealing a large difference in the nano-morphology of the polymer chains between DPP2T and DPP2T/PS films. To directly investigate the morphology of the DPP2T nanonetwork in DPP2T/PS, we first thoroughly rinsed the film with propylene glycol monomethyl ether acetate (PGMEA), which effectively dissolves PS but not DPP2T. Figure S19 presents 2D AFM images of the 7
PS-removed DPP2T/PS film. In the PS-removed DPP2T/PS film, we could observe a nanonetwork structure of DPP2T, which exhibited an extensively connected fibrillar structure with significantly reduced chain entanglement compared with a film of pure DPP2T (Fig. S18A) that was cast from a diluted DPP2T solution (15%) for a direct comparison of the morphological differences at the same DPP2T concentration, with and without PS. The critical role of PS in determining the structural characteristics of DPP2T is clearly evident. Additionally, these findings support our conclusion that the DPP2T forms a network structure at the bottom of a DPP2T/PS film, which remains even after the film has been thoroughly rinsed with PGMEA.
Note S5. Effective of the DPP2T/PS films. Given the smaller effective channel area in the DPP2T/PS films, the effective (eff) normalized to the effective channel coverage is expected to be higher than the normally measured device ; thus, eff will be a more relevant, intrinsic value, and its correlation with the charge-pathway structure created in the PS matrix will be more useful. The resultant eff values of the DPP2T/PS devices as a function of the effective channel coverage are shown in Fig. S20. The effective channel area was extracted via image thresholding of the TEM images (Fig. S21). Note that although this image analysis may not provide the exact value of the effective channel area, it enables us to qualitatively investigate the approximate channel coverage of the DPP2T/PS. The channel coverage and the corresponding eff were estimated in a range of DPP2T contents from 15% to 100%, where percolation is sufficient for reliable analysis. We find that eff exponentially decreases as the channel coverage broadens. However, GIWAXS analysis of the blend films reveals that the interchain stacking order gradually increases as the channel coverage increases (Fig. S22). 8
Therefore, the formation of a fibrillar network structure and its nanoscopic morphological features might be crucial factors that greatly improve the transport property despite the reduced interchain stacking order (see Figs. S23 and S24). Consequently, the eff of DPP2T/PS with the lowest interchain stacking order can be as high as 27 cm2 V1 s1, and the transport property approaches its intrinsic limit in a semiconducting polymer, despite the decreasing interchain stacking order. Note that the value of 27 cm2 V1 s1 that was obtained based on the approximate channel coverage extracted from the TEM images may not represent the exact of the DPP2T network in DPP2T/PS (15/85 wt %). However, this analysis clearly indicates that the intrinsic charge-transport properties of the DPP2T nanonetwork in DPP2T/PS can be significantly improved compared with those of neat DPP2T domains.
Note S6. Correlation between intermolecular structure and charge transport in DPP2T/PS. Although, no long-range interchain stacking order is observed, partial - ordering may exist at small length scales in DPP2T/PS. This short-range intermolecular aggregation is sufficient to promote efficient intramolecular charge transport along the polymer backbone (10, 11). Clearly, the interchain crystalline order is much higher in pure DPP2T than in DPP2T/PS. However, the structural and energetic disorder induced by chain entanglement and phase boundaries should also be much more prevalent in a pure DPP2T film, hindering charge transport. Furthermore, intramolecular charge delocalization is expected to be significantly hindered in the entangled DPP2T chains and fibrils of such a film. As a result, efficient intrachain charge transport should be suppressed; charges should be forced to undergo much more interchain hopping through localized states. These hypotheses 9
are consistent with our transport analyses. Extended, closely packed interchain - coupling should promote more efficient transport along both interchain and intrachain paths (12). However, our results demonstrate that reducing interchain interactions may improve the charge transport in solution-processable polymeric semiconductors and that reducing the interchain-aggregation-related structural disorder may be more important than altering the interchain ordering.
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III. Supplementary Figures
Fig. S1. Optical characteristics of PS. Transmittance spectrum of a PS thin film (40 nm). The inset shows the absorption spectrum of the PS film, indicating an optical band gap of 4 eV.
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Fig. S2. Optical characteristics of DPP2T and P3HT. Normalized absorption spectra of DPP2T and P3HT films. Inset shows the chemical structure of P3HT.
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Fig. S3. Optical spectroscopy of DPP2T and DPP2T/PS. Tr spectra of DPP2T/PS blend films at various concentration ratios. The inset shows the Ta values of DPP2T/PS blend films at various DPP2T concentrations. The curved line indicates the trend in Ta with the variation in the DPP2T concentration.
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Fig. S4. Structural analysis of DPP2T/PS. The elemental mapping of S (shown in green) in the DPP2T/PS film was obtained via energy-dispersive X-ray spectroscopy line-scan analysis. The scale bar represents 300 nm.
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Fig. S5. Structural analysis of PS. Normalized 2D GIWAXS image of a PS film. The wide arc-pattern around q 1.32 Å1 indicates that the PS is amorphous.
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Fig. S6. Structural analysis based on GIWAXS measurements. (A,B) Normalized 1D profiles of DPP2T, DPP2T/PS, and PS films along the (A) out-of-plane and (B) in-plane directions.
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Fig. S7. Cross-sectional diagram of a TGBC FET. The Au and Al serve as the bottom source/drain and top gate electrodes, respectively. Pure DPP2T or DPP2T/PS acts as the charge-transport layer. For the gate insulating layer, CYTOP (t 550 nm) is used. The measured capacitance of the CYTOP layer is 3.5 nF cm2.The channel length and width are 40 µm and 1000 µm, respectively.
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Fig. S8. Output characteristics of TGBC FETs at room temperature. (A) DPP2T. (B) DPP2T/PS. VGS varies from 0 V to 60 V. Both devices show clear FET characteristics with a low zero-VDS current, good IDS linearity in the linear regime, and the modulation of IDS with VGS.
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Fig. S9. Representative linear regime transfer characteristics of pure DPP2T and DPP2T/PS FETs under a VDS of 5 V.
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Fig. S10. Saturation distribution for DPP2T/PS (15/85 wt % ratio) FETs.
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Fig. S11. Hole values of DPP2T FETs at various DPP2T concentrations. The curved line indicates the trend in the hole value as the DPP2T concentration is varied. The vertical lines (whiskers) indicate the 10th-to-90th percentile ranges. The minimum and maximum values are indicated by asterisks.
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Fig. S12. T-dependent transfer characteristics of DPP2T FETs in the linear regime under various VDS. (A) 2 V. (B) 4 V. (C) 6 V. (D) 8 V. T was varied from 100 K to 310 K.
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Fig. S13. T-dependent transfer characteristics of DPP2T/PS FETs in the linear regime under various VDS. (A) 2 V. (B) 4 V. (C) 6 V. (D) 8 V. T was varied from 100 K to 310 K.
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Fig. S14. Schematic diagram of the local energy difference between aggregated and amorphous DPP2T regions.
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Fig. S15. Schematic illustration of the dominant charge-transport direction in pure DPP2T and DPP2T/PS films.
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Fig. S16. Measurements and modeling of T-dependent device characteristics. (A) Rendering of the measured transfer curves by means of the power-law current-voltage model on a semilogarithmic scale. The measured characteristics (symbols) for each T were fitted to the power-law relationship (solid lines). The channel length and width are 40 m and 1 mm, respectively, and VDS is fixed at 60 V. (B) Log-log plot of the IDS as a function of the effective gate overdrive voltage. VT is 0 V for a DPP2T FET and 8 V for a DPP2T/PS FET. (C) Extracted exponents as a function of 1/T for DPP2T and DPP2T/PS.
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Fig. S17. T-dependent transfer characteristics of DPP2T and DPP2T/PS devices. (A,B) Normalized IDS1/2-VGS curves of (A) DPP2T and (B) DPP2T/PS. These curves present the VGS dependence of IDS1/2 at varying temperatures, showing T-dependent behaviors that can be correlated with localized energy states. The lower T dependence of the DPP2T/PS curve indicates that DPP2T/PS exhibits reduced disorder compared with DPP2T. VDS is fixed at 60 V.
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Fig. S18. Structural analysis of pure DPP2T and DPP2T/PS. 2D top-surface images of diluted pure DPP2T (15%) and DPP2T/PS films measured using atomic force microscopy (AFM). (A,B) Topographic images of (A) pure DPP2T and (B) DPP2T/PS. (C,D) Phase images of (C) pure DPP2T and (D) DPP2T/PS. The scale bars represent 500 nm. (E,F) Corresponding surface 1D profiles for (E) pure DPP2T and (F) DPP2T/PS. Notably, the pure DPP2T film was deposited from a dilute DPP2T solution (15%) with the same DPP2T concentration as that of the DPP2T/PS solution but without PS. Despite dilution, pure DPP2T forms entangled fibrillar structures and, inevitably, abundant phase boundaries (phase image). We could not determine the exact DPP2T/PS structure from the AFM images, but a separated phase structure is evident in the phase image of the DPP2T/PS; the structure appears to show a DPP2T nanonetwork partially embedded in an amorphous PS matrix. 28
Fig. S19. 2D AFM images of PS-removed DPP2T/PS. (A) Topographic image. (B) Phase image. The scale bars represent 500 nm. (C) Corresponding 1D surface profile. Notably, the nanonetwork structure of DPP2T can be clearly observed in the PS-removed DPP2T/PS film.
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Fig. S20. Effective-channel-area-normalized eff versus channel-coverage percentile plot for PS-blend FETs. The effective channel area was extracted from various TEM images via image thresholding.
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Fig. S21. Estimation of the effective channel areas of DPP2T/PS films at various concentration ratios. (A–F) Transformed TEM images obtained via an image thresholding method for DPP2T/PS films with concentration ratios (wt % ratios) of (A) 15/85, (B) 30/70, (C) 50/50, (D) 70/30, (E) 80/20, and (F) 90/10. (G) Estimated channel area as a function of DPP2T content.
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Fig. S22. Structural analysis of DPP2T/PS. Normalized 2D GIWAXS patterns of DPP2T/PS films at various concentration ratios (wt % ratios): (A) 30/70, (B) 50/50, (C) 70/30, and (D) 100/0.
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Fig. S23. T-dependent characteristics of DPP2T/PS devices. (AD) T-dependent transfer characteristics of DPP2T/PS FETs in the linear regime at various concentration ratios of (A) , (B) (C) , and (D) under a VDS of 2 V. T was varied from 100 K to 310 K.
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Fig. S24. T-dependent characteristics of DPP2T/PS devices. (A) Arrhenius plots of the Tdependent linear values for DPP2T/PS FETs at various concentration ratios under a VDS of 2 V. (B) EA as a function of the DPP2T content in the high-T ( 190 K) and low-T ( 190 K) regimes for DPP2T/PS FETs.
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Fig. S25. Inkjet-printed PEDOT:PSS source/drain electrodes on a PEN substrate. The contact and channel regions are clearly defined by the inkjet-printing method. The estimated channel length is 100 µm. The scale bar represents 200 µm.
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Fig. S26. Large-area FT-FET device. A photograph of our all-solution-processed, all-polymer FT-FET device (10 cm 10 cm) containing an array of 1650 FETs. Because of its high transparency (Ta 86%) and colorless nature, we can see through the device without color distortion. It is even difficult to locate the individual FT-FETs with the naked eye.
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Fig. S27. Output characteristics of FT-FETs. VGS is modulated from 0 V to 60 V. The lateral-F dependence and waviness of the curves are attributable to the low conductivity ( 700 S/cm) of the polymeric metal (PEDOT:PSS) electrodes, in which quasi-free charge carriers are subject to substantial energetic disorder and trap-sites upon charge injection and transport, resulting in a F-dependent charge flow (i.e., conductivity) in PEDOT:PSS electrodes.
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Fig. S28. Transfer characteristics of FT-FETs before and after 1000 bending cycles at a bending radius of R 5 mm. We detect no performance degradation in the transfer characteristics even after 1000 bending cycles.
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Fig. S29. Schematic diagrams of FT-FET-PLED devices. (A) Cross-sectional device structure. (B) Energy band diagram for each layer.
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Fig. S30. Optical transmittance spectra of FT-FET-PLED devices. (A) Tr spectra of normal yellow PLED and integrated yellow FT-FET-PLED devices. (B) Tr spectra of the layers through which the emitted light passes in the normal yellow PLED and integrated yellow FTFET-PLED devices.
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Fig. S31. Optical characteristics of the light emitted from FT-FET-PLED devices. (A) CIE (1931) x-y color coordinates of the light emitted from normal PLED and integrated FT-FETPLED devices. (B–D) EL spectra of normal PLED and integrated FT-FET-PLED devices fabricated with (B) SPW-111, (C) MEH-PPV, and (D) F8BT.
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Fig. S32. Chemical structures of the semiconducting polymers used for the emissive layers. (A) PDY-132, (B) MEH-PPV, and (C) F8BT. The chemical structure of SPW-111 is not known.
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IV. Supplementary Tables Table S1. Mobility values of DPP2T and DPP2T/PS FETs with various concentration ratios. DPP2T a ()
DPP2T/PS
max
min
2
2
a ()
max
min
2
2
DPP2T contents (%)
(cm V s )
(cm V s )
(cm V s )
(cm V s )
(cm V s )
(cm V s )
1
-
-
-
0.0800 (0.0537)
0.163
0.0124
2
0.0787 (0.0630)
0.237
0.00693
0.153 (0.151)
0.399
0.00183
3
0.199 (0.120)
0.421
0.00762
0.516 (0.275)
1.079
0.217
5
0.323 (0.101)
0.499
0.139
0.888 (0.228)
1.29
0.601
8
0.490 (0.111)
0.747
0.355
0.964 (0.286)
1.48
0.598
10
0.440 (0.0952)
0.601
0.277
1.13 (0.277)
1.78
0.738
15
0.435 (0.0611)
0.518
0.321
1.56 (0.524)
3.07
0.872
20
0.523 (0.110)
0.785
0.418
1.16 (0.257)
1.60
0.715
25
0.591 (0.0951)
0.773
0.438
1.17841 (0.141)
1.41
1.01
30
0.594 (0.0937)
0.814
0.481
1.08359 (0.228)
1.47
0.618
50
0.660 (0.0897)
0.792
0.535
1.06 (0.219)
1.49
0.778
70
0.678 (0.105)
0.821
0.531
1.06 (0.175)
1.46
0.828
80
0.618 (0.0729)
0.748
0.484
0.853 (0.0824)
0.983
0.726
90
0.634 (0.102)
0.800
0.483
0.841 (0.0775)
0.977
0.701
100
0.679 (0.0809)
0.801
0.548
-
-
-
2
-1 -1
-1 -1
-1 -1
2
-1 -1
-1 -1
a is the average mobility. is the standard deviation. max and min are the maximum and the minimum mobilities, respectively.
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-1 -1
Table S2. Transmittance values of FT-FET devices with different layering conditions. Condition
Ta (%)
Tmax (%)
Tmin (%)
T550 (%)
1
85.9
89.1
76.0
87.5
2
85.5
88.3
76.2
87.8
3
85.7
87.8
76.2
87.6
4
87.7
90.7
78.5
88.9
All-layer
85.8
89.1
77.2
88.1
Ta is the average transmittance. Tmax and Tmin are the maximum and the minimum transmittances, respectively. T550 is the transmittance at 550 nm. These values were estimated in the visible range (from 400 nm to 700 nm). Condition 1 denotes a PEN substrate. Condition 2 denotes condition 1 + PEDOT:PSS (S/D) layer. Condition 3 denotes condition 2 + DPP2T/PS. Condition 4 denotes condition 3 + PMMA layer. All-layer denotes condition 4 + PEDOT:PSS (G) layer. These layering conditions are identical to the device-fabrication conditions.
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V. Supplementary References Reference 1. Li W, et al. (2013) Efficient small bandgap polymer solar cells with high fill factors for 300 nm thick films. Adv. Mater. 25(23):3182-3186. Reference 2. Kirkus M, et al. (2012) Optical properties of oligothiophene substituted diketopyrrolopyrrole derivatives in the solid phase: Joint j- and h-type aggregation. J. Phys. Chem. A 116(30):7927-7936. Reference 3. Zhang F, et al. (2013) Ultrathin film organic transistors: Precise control of semiconductor thickness via spin-coating. Adv. Mater. 25(10):1401-1407. Reference 4. Kronemeijer AJ, et al. (2014) Two-dimensional carrier distribution in top-gate polymer field-effect transistors: Correlation between width of density of localized states and urbach energy. Adv. Mater. 26(5):728733. Reference 5. Venkateshvaran D, et al. (2014) Approaching disorder-free transport in high-mobility conjugated polymers. Nature 515(7527):384-388. Reference 6. Vissenberg MCJM, Matters M (1998) Theory of the field-effect mobility in amorphous organic transistors. Phys. Rev. B 57(20):12964-12967. Reference 7. Horowitz G, Hajlaoui ME, Hajlaoui R (2000) Temperature and gate voltage dependence of hole mobility in polycrystalline oligothiophene thin film transistors. J. Appl. Phys. 87(9):4456-4463. Reference 8. Kalb WL, Batlogg B (2010) Calculating the trap density of states in organic field-effect transistors from experiment: A comparison of different methods. Phys. Rev. B 81(3):035327. Reference 9. Kim C-H, Bonnassieux Y, Horowitz G (2014) Compact dc modeling of organic field-effect transistors: Review and perspectives. Electron Devices 61(2):278-287. Reference 10. Zhang X, et al. (2013) Molecular origin of high field-effect mobility in an indacenodithiophene– benzothiadiazole copolymer. Nat. Commun. 4:2238. Reference 11. Wang S, et al. (2015) Experimental evidence that short-range intermolecular aggregation is sufficient for efficient charge transport in conjugated polymers. Proc. Natl. Acad. Sci. U. S. A. 112:10559-10604. Reference 12. Hsu BB-Y, et al. (2015) The density of states and the transport effective mass in a highly oriented semiconducting polymer: electronic delocalization in 1d. Adv. Mater. 27:7759-7765.
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