Supplementary Figure 1. EL spectral characteristics. (a)

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1 Supplementary Figure 1. EL spectral characteristics. (a) Angular dependence of normalized light intensity at 540 nm according to ZnO layers; Lambertian emission pattern (black square), ZnO-F (red circle), ZnO-R1 (green up-pointing triangle) and ZnO-R2 (blue diamond) at 5.5 V. Device configurations are FTO / several types of ZnO / 2-ME+EA / F8BT (100 nm) / MoO 3 / Au. All emission intensities were normalized with the emission intensity of the ipled with ZnO-F in the normal direction.

2 Supplementary Figure 2. (a) Schematic energy diagrams for flat band conditions the ZnO-R / 2-ME+EA / F8BT. (b) J-V characteristics of electron-only devices with and without 2-ME+EA.

3 Supplementary Figure 3. Photoluminescence (PL) spectra of F8BT on to ZnO-F and ZnO-R1 films with and without 2-ME+EA.

4 Supplementary Figure 4. Performances of ipleds devices using ZnO-R1 without (black square) and with (red circle) 2-ME+EA interlayer. (a) Current density versus voltage (J-V) characteristics, (b) luminance versus applied voltage (L- V, cd m -2 ), (c) luminous efficiency versus current density (LE-J, cd A -1 ), (d) power efficiency versus current density (PE-J, lm W -1 ), (e) EQE versus current density (EQE-J, %) and (f) normalized electroluminescence (EL) spectrum of ipleds at 100 ma cm -1.

5 Supplementary Figure 5. Performances of ipleds with 2-ME+EA and differently structured ZnO layers: ZnO-F (black square) and ZnO-R1 (red circle).

6 Supplementary Figure 6. Calculation of waveguide modes by the FDTD method. (a) Dispersion curve (TM modes) of ZnO-F. (b) Dispersion curve (TM modes) of ZnO-R1. (c) Dispersion curve (TE modes) of ZnO-F. (d) Dispersion curve (TE modes) of ZnO-R1. (e) Calculated grating period with respect to emission wavelength required to extract the waveguides modes.

7 Supplementary Table 1. Summarized device performances of ipleds using ZnO-R1 with and without 2-ME+EA interlayer. Device configuration Bias 10 ma/cm 2 Bias 1000 cd/m 2 L max [cd/m 2 ] LE max [cd/a] PE max [lm/w] EQE max [%] Turn-on voltage [V] w/o 2-ME+EA ,900 (10.4 V) 1.28 (9.8 V) 0.41 (9.8 V) 0.36 (9.8 V) 2.0 with 2-ME+EA ,500 (10.6 V) 17.3 (10.2 V) 6.60 (5.2 V) 4.91 (10.2 V) 2.0 Full devices : FTO / ZnO R1 / (2-ME+EA) / F8BT (200nm) / MoO 3 / Au Supplementary Table 2. Summarized device performances of ipleds using ZnO-F and ZnO-R1 with 2-ME+EA interlayer at 1200 nm of F8BT. Device configuration Bias 10 ma/cm 2 Bias 1000 cd/m 2 L max [cd/m 2 ] LE max [cd/a] PE max [lm/w] EQE max [%] Turn-on voltage [V] ZnO-F ,900 (22.4 V) 49.9 (22.4 V) 12.4 (7.6 V) 14.6 (22.4 V) 2.8 ZnO-R ,400 (20.6 V) 61.6 (20.4 V) 19.4 (4.8 V) 17.8 (20.4 V) 2.6 Full devices : FTO / ZnO X / 2-ME+EA / F8BT (1200nm) / MoO 3 / Au X: ZnO-F, ZnO-R1 Supplementary Table 3. Summarized excition lifetime of F8BT on the different ZnO layers with and without 2-ME+EA. Films configuration avr [ns] Quartz / F8BT 1.75 Quartz / ZnO-F / F8BT 1.44 Quartz / ZnO-F / 2-ME+EA / F8BT 1.61 Quartz / ZnO-R1 / F8BT 1.41 Quartz / ZnO-R1/ 2-ME+EA / F8BT 1.56 Quartz / ZnO-R2 / F8BT 1.28 Quartz / ZnO-R2 / 2-ME+EA / F8BT 1.38

8 Supplementary Table 4. Comparison of our work with previous literature. Previous literature Emission type Structure Emission color LE max [cd/a] PE max [lm/w] EQE max [%] S2 [Nat. Photonics, 2013] S3 [Nat. Photonics, 2012] S4 [Adv. Mater., 2010] S5 [Adv. Mater., 2010] S6 [Adv. Func. Mater., 2012] S3 [Nat. Photonics, 2012] S6 [Adv. Func. Mater., 2013] S7 [Adv. Mater., 2010] Our work PLEDs [Fluorescent] OLEDs [Phosphorescent] PLEDs [Fluorescent] Conventional Green Conventional Green Conventional Green 22.1 ~ Inverted Green 22.7 ~7 7.3 Inverted Green 27.6 ~ Conventional Green Conventional Green Inverted Green ~4 Inverted Green

9 Supplementary Discussion EL spectral characteristics. We observed angular dependence of normalized light intensity according to ZnO layers; Lambertian emission pattern (black square), ZnO-F (red circle), ZnO-R1 (green up-pointing triangle) and ZnO-R2 (blue diamond) to confirm the improved extraction of the wave-guide modes because of spontaneously formed ripple-shaped nanostructure of the ZnO layer in IPLEDs, as shown in Supplementary Fig. 1. All emission profiles of the ipleds with ZnO-F, ZnO-R1 and ZnO-R2 are closed to that of a Lambertian and the integrated EL intensities of ipled using ZnO-R1 (the dominant period of ~ 300 nm) were highly enhanced because of the extraction of the ZnO/organic mode trapped and reduction of in-plane WG losses. Performances of ipleds devices using ZnO-R1 with and without 2-ME+EA interlayer. To confirm the effect of solvent treatment on ZnO, device characterizations of ipleds devices using ZnO-R1 without (black square) and with (red circle) 2-ME+EA interlayer are observed, as shown in Supplementary Fig. 4. The optimized PLEDs with 2-ME+EA interlayer exhibited remarkably improvment in LE ( cd/a), PE ( lm W -1 ) and EQE ( %), which were improved by approximately 14, 16 and 14 fold higher than the reference ipled without 2-ME+EA, respectively (Supplementary Fig. 4 and Supplementary Table 1). Performances of ipleds with 2-ME+EA and differently structured ZnO layers. We observed the performance of thick device (1200 nm) with ZnO-F and ZnO-R1 treated 2-ME+EA in Supplementary Fig. 5 and Supplementary Table 2. The efficiencies of ipleds

10 (1200 nm) with ZnO-F and ZnO-R1 treated 2-ME+EA were LEs of 49.9 cd/a and 61.6 cd/a and EQEs of 14.6 % and 17.8 %, respectively. Note that the device efficiencies with ZnO-R1 treated 2-ME+EA are much higher than those with ZnO-F treated 2-ME+EA by approximately 23 % for LE and 22 % for EQE. These results strongly support our conclusion on the enhanced out-coupling due to the ripple structure in the thick ipleds. Exciton lifetime of F8BT on the ZnO layers with and without 2-ME+EA. We observed positive effect of 2-ME+EA solvent treatment of ZnO on electroluminescence of emissive polymer by measuring time-correlated single photon counting (TCSPC) and photoluminescence quantum efficiency (PLQE). The exciton life times of F8BT on ZnO-F, ZnO-R1 and ZnO-R2 without and with 2-ME+EA interlayer were observed and those with 2-ME+EA interlayer exhibited remarkably enhancement using ZnO- F ( ns), ZnO-R1 ( ns) and ZnO-R2 ( ns) at 540 nm, leading to the reduction of the exciton quenching becuase of the existance of 2-ME+EA interlayer on ZnO. The photoluminescence quantum efficiency (PLQE) measurement showed the same trend as those of TCSPC measurement with increased values ( %) for ZnO-F with 2-ME+EA interlayer, ( %) for ZnO-R1 with 2-ME+EA interlayer and ( %) for ZnO-R2 with 2-ME+EA interlayer (Supplementary Table 3). PL spectral measurement. To clarify the decrease of exciton quenching by 2-ME+EA treatment on ZnO, We measured the photoluminescence (PL) spectra of ZnO/F8BT, ZnO-R1/F8BT, ZnO-R/2- ME+EA/F8BT and ZnO-R1/2-ME+EA/F8BT (Supplementary Fig. 3). The intensities of

11 ZnO-F and ZnO-R1 with 2-ME+EA are much higher than those of ZnO-F and ZnO-R1 without 2-ME+EA that can support the reduced exciton quenching by amine-based polar solvent treatment on ZnO. Calculation of waveguide modes by the FDTD method. To elucidate the light extraction enhancements, we calculated the dispersion curves of the ideal flat device and the nanostructure-incorporated device by using the FDTD method. Supplementary Fig. 6 presents dispersion curves of the waveguide modes in the ipled structures and we confirmed that the calculated grating period is required to extract the waveguides modes.

12 Supplementary Methods Angular measurement. An angular stage was used to collect EL spectra at various angles from 0 to 80 while keeping the device stationary and moving the optical fibre attached to the multi-channel spectrometer (Ocean Optics, HR 2000+). A distance of 20 mm was maintained from the ipled devices with different ZnO layers at 5.5 V. s1 Electron only devices. The electron only devices (FTO / ZnO-R1 / F8BT / LiF / Al with and without 2-ME+EA treatment) were prepared. The J-V characteristics were measured using a Keithley 2400 Source Meter. PL measurement The PL intensities of the F8BT (10 nm) / ZnO-F or ZnO-R1 / quartz with and without 2- ME+EA were measured using photoluminescence spectroscopy (Edinburgh Instruments Ltd.). FDTD simulation. The dispersion curves were calculated using the two dimensional FDTD method. We assumed that the ZnO-R1 had a the corrugation period of 300 nm and a corrugation depth of 15 nm. The refractive indices of Au and ZnO were obtained from the literature, and the refractive indices of glass, FTO, F8BT and MoO 3 that were used in this calculation were 1.52, 1.85, 1.7 and 1.9, respectively. s1

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