Supporting Information

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1 Supporting Information Solution-Processed CuInS 2 -Based White QD-LEDs with Mixed Active Layer Architecture Svenja Wepfer 1,2, Julia Frohleiks 1,2, A-Ra Hong 3, Ho Seong Jang 3, Gerd Bacher, 2, Ekaterina Nannen * 1,2 1 Research Group Solid State Lighting, NanoEnergieTechnikZentrum, and 2 Werkstoffe der Elektrotechnik and CENIDE, University Duisburg-Essen, Duisburg, Germany 3 Materials Architecturing Research Center, Korea Institute of Science and Technology (KIST), 5, Hwarang-ro 14-gil, Seongbuk-gu, Seoul 02792, Republic of Korea Corresponding Author * Ekaterina.Nannen@uni-due.de S-1

2 1. PESA measurement of CIS/ZnS QDs We performed photoelectron emission spectroscopy in air (PESA) to confirm the HOMO levels of the CIS/ZnS and the ZnCdSe/ZnS QDs, respectively. We got 5.62 ev for the valence band level of CIS/ZnS and 5.82 ev for the valence band level of ZnCdSe/ZnS. Figure S 1: PESA measurements of CIS/ZnS (orange line) and ZnCdSe/ZnS (blue line) QDs to confirm the valence band energy in air (CIS/ZnS:5.62 evand ZnCdSe/ZnS: 5.82 ev). 2. Absorption measurement of CIS/ZnS-QDs compared to the PL sepctrum Figure S 2 shows the extinction coefficient (red line) of CIS/ZnS QDs compared to the PL spectrum (orange line). A distinct peak around 375 nm is observed, which can clearly be attributed to a pronounced ZnS shell, in agreement with literature 1,2. The inset shows a zoom of the extinction coefficient between 400 and 650 nm to demonstrate the absorption of the core. S-2

3 Figure S 2:Extinction coefficient (red line) and PL (orange line) of CIS/ZnS QDs. The inset shows a zoom of the extinction coefficient between 400 and 650 nm. 3. Lifetimes of CIS/ZnS and ZnCdSe/ZnS QDs As discussed in the manuscript, we used a double-exponentional fitting function to fit the transient PL responses of the CIS/ZnS QDs. In case of ZnCdSe/ZnS we used a triple exponential decay function for curve fitting. The resulting lifetimes and corresponding amplitudes are summarized in Table S 1. Table S 1: Lifetimes and amplitudes for the single QD layers nm and 480 nm) as well as the mixed layer (@ 593 nm 480 nm). Material Time constants (τ) & Relative amplitudes (A) τ 1 A 1 τ 2 A 2 τ 3 A 3 CIS/ZnS 105 ns 34 % 320 ns 66 % - - ZnCdSe/ZnS 0.8 ns 10 % 7.8 ns 57 % 23.1 ns 33 % CIS/ZnS (mixed) 100 ns 39 % 320 ns 61 % - - ZnCdSe/ZnS (mixed) 0.7 ns 11 % 6.6 ns 58 % 19.3 ns 31 % S-3

4 4. Confocal measurement of the device We performed confocal measurements of the device surface of a complete layer stack (ITO, PEDOT:PSS, poly-tpd, mixed QD layer, ZnO) with a QD mixing ratio of 1:0.5. The whole layer stack exhibits a roughness Ra = 8 nm, which implies good quality of each underlying layer. We carefully chose orthogonal solvents for each subsequent layer to avoid any destruction of the pre-coated layers by spin-casting of another layer. Figure S 3: Confocal images of the device surface of a complete layer stack with a QD mixing ratio of 1: PL and EL spectra of mono- and bi-chromatic layers/devices Figure S 4 shows the PL (dotted lines) and EL (solid lines) spectra for the single components (ZnCdSe/ZnS in blue, CIS/ZnS in orange) as well as for the mixed layer (black). We observe a shift between PL and EL for both monochromatic devices (~ 70 mev for ZnCdSe/ZnS, ~130 mev for CIS/ZnS). The mixed devices/layers show no additional spectral shift or broadening but are comparable to the added emission of the monochromatic layers/devices (see Table S 2). S-4

5 Figure S 4: Top: PL (dashed lines) and EL (solid lines) spectra for monochromatic CIS/ZnS (orange) and ZnCdSe/ZnS (blue) layer/devices. Bottom: PL (dashed line) and EL (solid line) spectra for the mixed layer/device with a mixing ratio of 1:1. Table S 2: PL and EL characteristics of mono- and bi-chromatic devices. Peak Position (ev) fwhm (ev) PL EL PL EL PL EL PL EL ZnCdSe/ZnS CIS/ZnS Mixed (1:1) Peak variation in white QD-LEDs with different mixing ratios Figure S 5 a-c show the EL spectra for all mixing ratios (CIS/ZnS:ZnCdSe/ZnS volume mixing ratios 1:1, 1:0.5 and 1:2) as a function of the applied voltage. The contribution of ZnCdSe/ZnS and CIS/ZnS emission varies with increasing voltage. We observe no significant peak shift, neither for the blue emission nor for the orange emission. The exact peak positions for all devices as a function of the applied voltage are also summarized in Figure S 5 d. S-5

6 Figure S 5: EL spectra as function of applied voltage for devices with different mixing ratios (a-c) and corresponding peak positions (d). 7. Emission profile simulations for bi-chromatic white QD-LEDs To reveal the potential of high color rendering, bi-chromatic white QD-LEDs, we performed simulations to find the theoretical maximum for the CRI. With the materials used in this work (peak wavelength of ZnCdSe/ZnS QDs at 493 nm, peak wavelength of CIS/ZnS QDs at 630 nm, fwhm kept constant), we can obtain a maximum CRI of 81 by optimizing only the relative contributions of QD emission intensity. Following the bi-chromatic approach, high CRI values up to 89 can be obtained by shifting the EL peak positions to lower wavelengths (see Error! Reference source not found.) and still keeping the fwhm constant. This could be realized by using Zn x Cd 1-x Se/ZnS and CIS/ZnS QDs with different material composition (offstoichiometry of higher Cu defects and doping) and/or size. To reach a CRI exceeding 90, an increase of the fwhm is required or a third color component in the green spectral region (e.g. S-6

7 InP/ZnS) should complement the device. Figure S 6 additionally shows a simulated spectrum with increased fwhm for both QDs which leads to an increased CRI of 94. Figure S 6: Orange: Simulated EL spectrum of a bi-chromatic QD-LED with a CRI of 89. In this case the fwhm is as discussed in the manuscript, while the peak positions and emission intensities are optimized. Grey: Simulated EL spectrum of a bi-chromatic QD-LED with a CRI of 94 by additionally increasing the fwhm of both QD emissions. S-7

8 REFERENCES (1) Arai, T.; Senda, S.; Sato, Y.; Takahashi, H.; Shinoda, K.; Jeyadevan, B.; Tohji, K. Cu- Doped ZnS Hollow Particle with High Activity for Hydrogen Generation from Alkaline Sulfide Solution under Visible Light. Chem. Mater. 2008, 20 (5), (2) Zheng, J.; Yuan, X.; Ikezawa, M.; Jing, P.; Liu, X.; Zheng, Z.; Kong, X.; Zhao, J.; Masumoto, Y. Efficient Photoluminescence of Mn 2+ Ions in MnS/ZnS Core/Shell Quantum Dots. J. Phys. Chem. C 2009, 113 (39), S-8