Supplementary Information. Light Manipulation for Organic Optoelectronics Using Bio-inspired Moth's Eye. Nanostructures

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1 Supplementary Information Light Manipulation for Organic Optoelectronics Using Bio-inspired Moth's Eye Nanostructures Lei Zhou, Qing-Dong Ou, Jing-De Chen, Su Shen, Jian-Xin Tang,* Yan-Qing Li,* and Shuit-Tong Lee* 1. Procedures Involved in the Fabrication of Negative and Positive PFPE Molds The fabrication process of biomimetic perfluoropolyether (PFPE) molds with moth s eye nanostructures (MENs) is depicted in Figure S1. Firstly, the solution of [Ag(NH 2 ) 2 ]OH xh 2 O was prepared by 0.2 g AgNO 3 (AR), 0.12 g NaOH (AR), 10 ml NH 4 OH and 250 ml H 2 O, and the solution of C 6 H 12 O 6 was prepared by 0.2 g glucose and 250 ml H 2 O. Si substrate was dipped into the mixed solution of [Ag(NH 2 ) 2 ]OH xh 2 O and C 6 H 12 O 6 with a mixed ratio of 1:1, and sonicated for approximately 6 s by ultrasonic cleaner (DR-MH280, Derui Ultrasonic equipment), resulting in a ~10 nm-thick Ag layer deposited on Si substrate. Then, the substrate was transferred into rapid annealing system, and was annealed at 400 C for 1 min to form Ag NPs under nitrogen environmental condition. Thirdly, reactive ion etch (RIE) process (using tegal 903e RIE by REFURBISHED) was taken to generate biomimetic moth s eye nanostructures since Ag NPs can act as a mask. Finally, the Ag mask was removed by nitric acid and treated by plasma process to forming quasi-periodic nanocone structures. The shape and size of the nanocone can be controlled by adjusting the sizes of Ag NPs and the etching parameters. To fabricate the negative PFPE mold, a photocurable liquid PFPE precursor solution consisting of 1000 g mol -1 PPFP α, Ω-functionalized dimetha-crylate and the 1

2 photoinitiator 2,2-diethoxyacetophenone was poured over the Si template, and embossed under a constant pressure of 0.8 bar with UV illumination at a wavelength of 395 nm at 500 mj cm -2 for 10 s. On the contrary, prior to the fabrication of a positive PFPE mold, the UV resin was drop-casted on Si template followed by mold transfer. Then, the positive PFPE mold can be easily done by following the procedures involved in the fabrication of negative PFPE mold. 2

3 Figure S1. Schematic of the procedures involved in fabrication of positive and negative PFPE molds. a, Formation of Ag film on Si wafer substrate through the solution of [Ag(NH 2 ) 2 ]OH xh 2 O. b, Formation of Ag nanoparticles (NPs) through rapid thermal annealing. c, Patterning the Si wafer for the formation of moth s eye nanostructures with Ag NPs as a mask by using reactive ion etching (RIE) method. d, Formation of quasi-periodic nanocone structures by plasma cleaning process. e, Embossing PFPE film on patterned Si mold by mold transfer and UV curing process. f, Lift off PFPE film to form the negative mold. g, Dipping UV-curable resin on Si mold substrate followed by mold transfer. h, Embossing PFPE film on UV-hardened resin mold by mold transfer and UV curing process. i, Lift off PFPE film to form the positive mold. 3

4 2. PFPE Molds Used for Fabrication of MENs in OLEDs and OSCs Figure S2. AFM image of the positive PFPE mold with 200 nm-period MEN for the patterned organic layers in OLEDs. The PFPE mold possesses a period of 200 nm, a linewidth of 120 nm, a groove depth of 300 nm, and a duty cycle of

5 Figure S3. AFM image of the positive PFPE mold with 400 nm-period MEN for the patterned organic layers in OSCs. The PFPE mold possesses a period of 400 nm, a linewidth of 240 nm, a groove depth of 480 nm, and a duty cycle of

6 Figure S4. AFM image of the negative PFPE mold with 200 nm-period MEN for the patterned UV resin on the glass surface. The PFPE mold possesses a period of 200 nm, a linewidth of 120 nm, a groove depth of 300 nm, and a duty cycle of

7 3. Fabrication Process for Organic Devices with dual-side MENs Figure S5. Schematic of the procedures involved in the fabrication of dual-side MENs by nanoimprint lithography. a, Spin-coating PEDOT:PSS or ZnO layers on ITO substrate. b, Placing PFPE mold on substrate. c, Imprinting PFPE pattern with pressure and temperature. d, Lift off the mold. e, Deposition of the active layer. f, Imprinting on the glass surface. 7

8 4. Surface morphology of patterned organic optoelectronic devices with MEN Figure S6. Atomic force microscope (AFM) images of OLED and OSC with MENs. a-c, Morphological evolution of the surface after deposition of single (a), double (b), and triple (c) EL units on MEN-patterned PEDOT:PSS substrate. d, View of the top of OSC after the spin-coating of PTB7:PC 71 CM layer on MEN-patterned ZnO layer. 8

9 5. Performance Characteristics of OLEDs with MEN Figure S7. Performance characteristics of OLEDs. Current efficiencies versus luminance (cd m -2 ) of representative OLEDs without MEN (filled symbols) and with dual-side MEN (open symbols), which combine a MPE structure with single (a, squares), double (b, circles), and triple (c, triangles) EL units. Filled and open stars in a-c represent the devices only using internal and external MEN, respectively. 9

10 Figure S8. Angular dependence of emission spectra of OLEDs. Normalized EL intensities of devices without MEN (a) and with internal (b), external (c), and dual-side (d) MEN as a function of viewing angle. The inset compares the normalized EL spectra at a viewing angle of 0 and

11 Figure S9. Performance characteristics of blue and red OLEDs. a,c, J-V characteristics of blue (a) and red (c) OLEDs without MEN (filled symbols) and with dual-side MEN (open symbols). The blue OLEDs were constructed with a structure of ITO/PEDOT:PSS/TAPC (45 nm)/mcp:firpic (8 wt%, 20nm)/TmPyPb (35 nm)/lif (0.5 nm)/al (100 nm). The device structure of red OLEDs were ITO/PEDOT:PSS/NPB (40 nm)/dcjtb:alq 3 (3 wt%, 20 nm)/alq 3 (40 nm)/lif (0.5 nm)/al (100 nm). Inset in a and c: Normalized EL spectra for blue and red OLEDs, measured from the surface normal at J = 1 ma cm -2. b,d, External quantum efficiency versus luminance of blue (b) and red (c) OLEDs without MEN (filled squares) and with internal MEN (filled stars), external MEN (open triangles), dual-side MEN (open squares). 11

12 6. Optical properties of glass substrate with MENs Haze Measurement: Total transparency and specular transparency measurements were taken with and without integrating sphere, respectively. The transmittance of air was taken and used as a baseline measurement. The haze of PEDOT:PSS-coated ITO glass and ZnO-coated ITO glass substrates was calculated by generating the transmittance values into the formula, haze = (total transmittance - specular transmittance)/total transmittance. Figure S10. Percentage of transmitted light that is scattered (haze) for ITO-glass substrates with MENs. Haze versus wavelength for PEDOT:PSS-coated ITO glass substrates used in OLEDs (filled symbols) and for ZnO-coated ITO glass substrates used in OSCs (open symbols) without MEN (squares) and with dual-side MEN (circles). 12

13 7. Theoretical Analysis According to simulation results for TM polarized light at 450 nm and 800 nm presented in Supplementary Fig. S11, the experimental EQE enhancement peak in the region around 450 nm is due to the excitation of waveguide mode, in which the Bragg scattering in quasi-periodic photonic structures with modulated refractive indices result in standing waves by constructive interference between the traveling waves 1,2. The enhancement peak around 800 nm over the absorption tail of the active layer is due to surface plasmonic resonance. The weak absorption of PTB7:PC 71 BM at 800 nm cannot induce significant photocurrent, so that the EQE enhancement around this region is not experimentally observed. 13

14 Figure S11. Simulations of enhancement of light trapping in OSCs. a,b, Distribution of the magnetic field intensity in OSCs at the wavelength of incident TM polarized light of 450 nm (a) and 800 nm (b). 14

15 References 1. Sha, W. E. I., Choy, W. C. H. & Chew, W. C. Angular response of thin-film organic solar cells with periodic metal back nanostrips. Opt. Lett. 36, (2011). 2. You, J. B., Li, X. H., Xie, F. X., Sha, W. E. I., Kwong, J. H. W., Li, G., Choy, W. C. H. & Yang, Y. Surface Plasmon and Scattering-Enhanced Low-Bandgap Polymer Solar Cell by a Metal Grating Back Electrode. Adv. Energy Mater. 2, (2012). 15