Supporting Information. High-Performance Flexible Organic Light-Emitting Diodes. Using Embedded Silver Networks Transparent Electrodes

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1 Supporting Information High-Performance Flexible Organic Light-Emitting Diodes Using Embedded Silver Networks Transparent Electrodes Lei Zhou, 1, Heng-Yang Xiang, 1, Su Shen, 2, Yan-Qing Li, 1, * Jing-De Chen, 1 Hao-Jun Xie, 1 Irene A. Goldthorpe, 3 Lin-Sen Chen, 2 Shuit-Tong Lee, 1 and Jian-Xin Tang 1, * 1 Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou , China 2 College of Physics Optoelectronics and Energy, Soochow University, Suzhou , China 3 Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, N2L 3G1, Canada * Corresponding authors. addresses: jxtang@suda.edu.cn (J.X. Tang), yqli@suda.edu.cn (Y.Q. Li). These authors contributed equally. 1

2 1. Performance comparisons of flexible OLEDs Table S1. Summary of state-of-the-art flexible OLEDs reported in the literature in comparison with this work. Published device performance of OLEDs on graphene, Ag NWs, PEDOT:PSS and Ag grids transparent electrode. 1-7 Ref. Electrode Substrate Color Area 1 Multilayer graphene PET 2 Single-layer graphene (with half-sphere) Glass (mm 2 ) 3 Ag-NW-PVA Ag-NW-PVA Green Ta 2 O 5 /Au/MoO3 (Microcavity effect) Ag-NW (with outcoupling ) Efficiency Green 10 ~102.7 lm W cd m -2 White 10 ~17 cd A cd m -2 Green 10 ~250 cd A cd m -2 White lm W cd m -2 ~2.13 cd A cd m -2 (2.43 cd A Plastic Green 2 ~130 lm W cd m -2 Glass White cd A cd m lm W cd m -2 6 SWCNT/Ag-NW (with outcoupling) Polymer Green 10 White 10 ~20 cd A cd m -2 (111.1 cd A ~41 lm W cd m -2 (44.0 lm W 7 ITO (high index glass & outcoupling) Glass White lm W cd m -2 Green cd A cd m -2 Our work Embedded Ag nanograting (with outcoupling) PET White lm W cd m cd A cd m lm W cd m -2 2

3 2. Performance roll-off characteristics for flexible green OLEDs Table S2. Performance roll-off characteristics of current efficiency (CE) and external quantum efficiency (EQE) for flexible green OLEDs (size: 12 mm 12 mm) at a luminance of 1,000 cd m -2 and 10,000 cd m -2. The values in parentheses depict the decreasing ratios when the luminance is increased from 1,000 cd m -2 to 10,000 cd m -2. Device structures CE (1,000 cd m -2 ) (cd A -1 ) EQE (1,000 cd m -2 ) (%) ITO PEAN PEAN (outcoupling) CE (10,000 cd m -2 ) (cd A -1 ) 17.9 (29.2%) 47.8 (16.4%) (7.6%) EQE (10,000 cd m -2 ) (%) 7.1 (19.3%) 17.7 (9.7%) 47.3 (5.2%) 3

4 3. The characteristics of the PET with embedded Ag networkss (PEANs) Figure S1. Transmission spectra of bare PET, ITO/PET substrate and PEANs with various hexagonal periods. 4

5 Figure S2. Comparison of various materials as flexible transparent conductive electrodes. (a) Sheet resistance versus optical transmission (at 550 nm) for PEANs (this work), ITO/glass substrate, 8 ITO/PET substrate, 9 graphene, 10 Ag nanowires (NWs), 11 carbon nanotubes (CNTs) 12 and Ag-surface-grid. 13 The periods of PEANs included here are 25 µm, 50 µm, 100 µm and 150 µm, respectively. (b) Sheet resistance versus optical transmission (at 550 nm) for PEANs and composite electrode (PEAN coated with an 80 nm-thick PEDOT:PSS layer) 5

6 Figure S3. Percentage of transmitted light that is scattered (Haze) for various PEANs. Haze versus wavelength for PEANs with various Ag nanograting periods (spheres), bare PET substrate (diamonds) and ITO-PET substrates (triangles), which were obtained by collecting the total transmittance and the specular transmittance with in integrating sphere [haze = (total transmittance - specular transmittance)/total transmittance]. 6

7 Figure S4. The scratch resistance test for PEANs in comparison with ITO-PET substrates. The variation in sheet resistances of PEAN and ITO-PET during repeated scratching according to ISO15184:

8 4. Morphologies of flexible OLED devices Figure S5. Scanning electron microscopy (SEM) images of PEANs and the flexible OLED device using PEAN as a transparent anode. (a) Top-view of the embedded Ag nanograting on a PET substrate. (b) Cross-sectional image of an OLED constructed on a PEAN. 8

9 Figure S6. Atomic force microscopy (AFM) images of PEDOT:PSS layers spincoated on flexible substrates. (a) View of the PEDOT:PSS layer on a ITO-coated PET substrate, showing a root-mean-square (RMS) roughness of ~3.2 nm. (b) View of the PEDOT:PSS layer on PEANs, showing a RMS roughness of ~8.7 nm. 9

10 5. Device performance of green OLED devices Figure S7. Device performance of green OLEDs constructed on various substrates with different emission areas. (a) Current efficiency as a function of luminance. (b) Luminance as a function of current density. The poor performance of OLEDs on an 10

11 ITO-PET substrate compared to that on a glass substrate is mainly ascribed to the inherent limitation by the ITO deposition temperature on plastic substrates. 14 (c) Normalized emission spectra for flexible green OLEDs on ITO-glass and PEAN substrates without outcoupling structure. The insets show the photographs of flexible green OLED device (0.33 mm 0.33 mm) using PEANs as anode under the off and on conditions. 11

12 Figure S8. Calculation of light extraction enhancement. Simulated EQE intensity (at a wavelength of 520 nm) as a function of viewing angle using the Monte Carlo ray tracing method, and three dimensional irradiance images for OLEDs using PEANs and ITO as anodes, respectively (inset). 12

13 Figure S9. Simulated distributions of waveguide modes by FDTD method. Distributions of electric field intensity for TE 0, TM 0 and TM 1 modes at λ = 520 nm in flat device structures using ITO (a) and PEANS (b) as an anode. 13

14 Figure S10. Performance stability of flexible OLEDs during the bending tests. (a) Changes in current efficiency of green OLEDs using PEANs and ITO as the anode during repeated bending. (b) Optical microscopy images of the devices after 0, 300, and 600 bending cycles. 14

15 6. Outcoupling structure used for light extraction and improved device performance Figure S11. AFM image of the nanostructured PEDOT:PSS layer on a PEANS. The deterministic aperiodic nanostructures (DANs) were patterned on the PEDOT:PSS layer with period = 400 nm, duty cycle = 0.6 and groove depth = 50 nm. 15

16 Figure S12. SEM image of a microlens array (MLA) on the PET surface. The hexagonal array of hemispherical microlenses mounted on the substrate surface with an index matching gel have a diameter of 50 µm and a fill factor of

17 Figure S13. Device performance of flexible green OLEDs using PEANs with an outcoupling structure. Current efficiency and power efficiency as a function of luminance for devices without (spheres) and with an outcoupling structure of only DANs (triangle) and DANs+MLAs (open circles). 17

18 Figure S14. Simulation of an OLED device using a PEANs without an outcoupling structure. (a) Calculated dispersion diagrams of TM (or TE) polarized light as a function of frequency and the in-plane wave vector Kx in the first Brillouin zone of the device. (b) Photon flux diagrams of the poynting vector S distribution. Red arrows depict the direction of the photon flux. 18

19 7. Device performance of white OLED devices Figure S15. Device performance of flexible white OLEDs using PEANs with an outcoupling structure. Current efficiency and power efficiency as a function of luminance for devices without (spheres) and with an outcoupling structure of only DANs (triangle) and DANs+MLAs (open circles). 19

20 Figure S16. Angular dependence of emission spectra from flexible white OLEDs using PEANs. EL spectra versus viewing angle for flexible white OLEDs without (a) and with (b) an outcoupling structure. 20

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