Supporting Information

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1 Supporting Information Time-dependent p-i-n structure and emission zone in sandwich-type light-emitting electrochemical cells Sandra Jenatsch a, *, Markus Regnat b, Roland Hany c, Matthias Diethelm c, Frank Nüesch c, Beat Ruhstaller a,b a Fluxim AG, Technoparkstrasse 2, 8406 Winterthur, Switzerland b Zurich University of Applied Sciences ZHAW, Institute of Computational Physics, Technikumstrasse 9, 8401 Winterthur, Switzerland c Empa, Swiss Federal Institute for Materials Science and Technology, Laboratory for Functional Polymers, 8600 Dübendorf, Switzerland * sandra.jenatsch@fluxim.com S1

2 Angular measurement setup details The home-built angular spectrometer setup consists of a half cylinder lens, a rotational stage with a detector unit (polarizer, spectrometer, 1 mm diameter pinhole and retarder). In the measured angular range between -70 to +70 an accuracy of ±1 is achieved. Figure S1. (a) Schematic illustration of the measurement setup and the operating LEC. (b) Regimes of an optical measurement; either the detection cone is smaller than the source or it is bigger. In the case of the widespread source regime, the measurement area is increasing with higher angle by a factor 1/cos(α). In the main text Figures 4 and 6, the 70 angle emission is notably lower than the simulation, especially compared to lower angles. We think that it is due to a limitation of the optical system: An optical measurement is either in the regime of a widespread source or a dot-like source as shown in Figure S1b. A characteristic of the widespread source regime is the increase of the measured area on the source with higher angle alpha, because the detection cone stays the same. To compare it to a measurement where the detection cone is larger than the source as in the dot-like source regime, a S2

3 correction factor cos(α) has to be applied. Our angular emission setup is in the widespread source regime and the simulation software takes an increasing area into account. We assume that at 70 where the measurement area is roughly 3 times larger (1/cos(70 )=2.92), the measurement spot moves partially out of the active LEC area, thereby reducing the effective measured area and consequently the measured light intensity is lower than the simulated one. Transient voltage and luminance Figure S2. Transient voltage (blue) and luminance (red) of the Cy3-P LEC operated under constant 50 ma cm -2. Influence of doping on IPCE/absorption analysis Due to the high solubility of the Cy3-P salt in various organic solvents it is not possible to experimentally determine the refractive indices of doped films in a cyclic voltammetry setup as proposed by Lanz et al. S1 We therefore first estimate the imaginary part of the Cy3-P refractive index from the absorption of a purely p-doped film presented in reference [S2] and using a dye-toradical ratio of the extinction coefficient of 2, as typically observed for cyanine dyes. S3 The real part of the refractive index was then calculated using the Kramers-Kronig relation assuming n = 1.7. For the refractive index of n-doped Cy3-P the p-doped nk data was shifted by 75 nm to the blue to reproduce the maximum absorption range published in reference [S4] (Figure S3(b)). As a typical doping concentration we assume 10% which is in line with findings presented in our previous publication. S5 The refractive indices of the 10% doped films (Figure S3(c)) were calculated from a linear effective medium approximation implemented in Setfos ( S3

4 Figure S3. Refractive indices of undoped (a), purely p- or n-doped (b) and 10% p- or n-doped (c) films of Cy3-P. These refractive indices of the 10% p- and n-doped layers are now used in the absorption simulation to determine the intrinsic region absorption for illumination through ITO or Ag, respectively. The chosen p-i-n situation consisted of a 40 nm thick intrinsic region which was swept through the 85 nm active layer. The absorption ratio at 550 nm was calculated for different centers of the intrinsic region and compared to the absorption ratio if only the refractive index for undoped Cy3-P was used in the simulation (see Figure S4). Figure S4. Simulated intrinsic layer absorption ratio at 550 nm with undoped refractive index (blue) or 10% doped refractive indices (orange) for the doped regions. The experimental point for the situation at t = 350 min is also included for reference. S4

5 Some deviations between the two calculated ratios can be observed. They are most pronounced if the intrinsic layer extends almost to the PEDOT:PSS or Alq 3 interfaces. Our experimental IPCE ratio lies however at a position where the difference between the two approaches is negligible. At most, the effect of 10% would for this situation lead to a mispositioning of < 0.05 which is approximately the experimental uncertainty of IPCE measurement on different devices. Simulated intrinsic layer absorption Figure S5. Simulated i-layer absorption for a fixed thickness of 40 nm with varied position (a + c; 0 = PEDOT:PSS/Cy3-P and 1 = Cy3-P/Alq3 interface) or a fixed position of 0.6 with varied i-layer thickness (b + d). The device is illuminated through the ITO (a + b) or the Ag (c + d) electrode. S5

6 Photocurrent measurements of super-yellow LECs We fabricated super-yellow LECs as described below. We measured the photocurrent as well as the IPCE after biasing the device with a constant current of 5 ma cm -2 for 250 min, leading to a luminance of 340 cd m -2 (6.8 cd A -1 ). The subsequently measured photocurrent is 5 µa cm -2, which is in agreement with reported values for polymer LECs. S6 The IPCE signal was below the noise level of our equipment (0.05%) and could not be measured therefore. A suitable method to get information about the emission zone for this system would rather be the angular emission measurement method. Figure S6. Transient voltage (blue) and luminance (red) of the super-yellow LEC operated under constant 5 ma cm -2. Figure S7. Current-voltage measurement directly after biasing the super-yellow LEC for 250 min at 5 ma cm -2. The photocurrent is 5 µa cm -2. S6

7 Fabrication of Super Yellow LECs: lithium trifluoromethansulfonate (Li-TFMS, Sigma-Aldrich, %), trimethylolpropane ethoxylate (TMPE, Sigma-Aldrich, average Mn ~450) and super yellow (SY, Merck) were dissolved separately in tetrahydrofuran (THF, Sigma-Aldrich, anhydrous, 99.9%, inhibitor-free) in concentrations of 10 mg ml -1 (Li-TFMS, TMPE) and 5 mg ml -1 (SY), respectively, and were stirred for at least 6 h at 60 C. The spin-coating solution was mixed from the precursor solutions in the mass ratio 1:0.1:0.03 (SY:TMPE:Li-TFMS) and was stirred again for at least 6 h at 60 C. For LECs, the spin-coating solution was deposited at 2000 rpm inside a nitrogen-filled glovebox onto clean, pre-patterned ITO substrates (see experimental section in the main part). Spin-coated films were dried at 60 C for 1 h. Finally, Al top electrodes were thermally evaporated through a shadow mask defining cells with an active area of 3.1 or 7.1 mm 2. S7 Simulated 0 -emission varying the position of the delta emitter Figure S8. Simulated normalized s-polarized emission at 0 for varying position of a delta emitter inside the cyanine layer. The closer the emitter to the Ag electrode the larger the ratio between the first and the second emission peak. S7

8 Time evolution of s-polarized 0 -emission Figure S9. Normalized s-polarized emission spectrum at 0 as a function of operation time. Within the accuracy of the measurement no change is observed, indicating a rather constant EZ over the entire time of the experiment. Figure S10(a) shows the first-to-second peak ratio of the experimental spectra at 0 (Figure S9) as a function of operation time. The error bars indicate the noise in the spectral data. This ratio can directly be compared with the ratio in the simulation as a function of delta emitter position (Figure S10(b)). From this comparison a strong change of the emission zone (EZ) during constant current operation of the investigated Cy3-P LEC is excluded. Maybe a slight shift of the EZ moving closer to the anode interface with operation time could be interpreted in the data. However, within the accuracy of the experimental data there is not a clear shift of the EZ. Figure S10. (a) First-to-second peak ratio of the experimental spectra at 0 versus operation time. (b) Simulated peak ratio as a function of delta emitter position. S8

9 Simulated 0 -emission with and without reabsorption postprocessing Figure S11. Simulated normalized s-polarized emission at 0 with completely transparent Cy3-P layer (blue) or when dividing the Cy3-P layer in three layers (inner one contains the emitter) and setting the outer ones absorbing (red). As expected from the overlap in emission and absorption (Figure 1, main text) the first peak decreases in intensity when reabsorption is allowed. Description of the applied emission zone fitting procedure An emission zone profile can be seen as an ensemble of many peak-like emitters with different intensities along the emissive layer resulting from dipoles placed at different positions. Mathematically, the fitting procedure tries to find the best set of weight coefficients of emission delta peaks at different positions inside the emissive layer to reproduce the measured emission spectrum. Thereby the outcoupled emission of each delta peak is calculated separately and superimposed in the end. The algorithm is not testing every possible combination of delta peaks, there are some restrictions that prevent solutions which are not physically meaningful. For example, negative intensities are excluded and the curvature of the EZ is forced to be monotonic and smooth since it is not expected that emitter intensity jumps randomly along the emissive layer. Also, no analytical function for the EZ is imposed. More details about this fitting procedure have been S8, S9 presented by Perucco et al. S9

10 Figure S12. (a) Dipole emitters with different intensities which show an unphysical solution for the EZ fitting problem. (b) Reasonable physical solution, without negative intensities and smoothed sequence of adjacent dipole emitters, representing a possible solution of the EZ fitting problem. SI References (S1) Lanz, T.; Lindh, E. M.; Edman, L. On the Asymmetric Evolution of the Optical Properties of a Conjugated Polymer during Electrochemical P- and N-Type Doping. J. Mater. Chem. C 2017, 5, (S2) Fan, B.; de Castro, F. A.; Heier, J.; Hany, R.; Nüesch, F. High Performing Doped Cyanine Bilayer Solar Cell. Org. Electron. 2010, 11, (S3) Lenhard, J. R.; Cameron, A. D. Electrochemistry and Electronic Spectra of Cyanine Dye Radicals in Acetonitrile. J. Phys. Chem. 1993, 97, (S4) De Jonghe-Risse, J.; Heier, J.; Nüesch, F.; Moser, J.-E. Ultrafast Charge Transfer in Solid-State Films of Pristine Cyanine Borate and Blends with Fullerene. J. Mater. Chem. A 2015, 3, (S5) Jenatsch, S.; Wang, L.; Bulloni, M.; Véron, A. C.; Ruhstaller, B.; Altazin, S.; Nüesch, F.; Hany, R. Doping Evolution and Junction Formation in Stacked Cyanine Dye Light-Emitting Electrochemical Cells. ACS Appl. Mater. Interfaces 2016, 8, (S6) Leger, J. M.; Patel, D. G.; Rodovsky, D. B.; Bartholomew, G. P. Polymer Photovoltaic Devices Employing a Chemically Fixed P-I-N Junction. Adv. Funct. Mater. 2008, 18, (S7) Jenatsch, S.; Wang, L.; Leclaire, N.; Hack, E.; Steim, R.; Anantharaman, S. B.; Heier, J.; Ruhstaller, B.; Penninck, L.; Nüesch, F.; Hany, R. Visible Light-Emitting Host-Guest Electrochemical Cells Using Cyanine Dyes. Org. Electron. 2017, 48, (S8) Perucco, B.; Reinke, N. A; Rezzonico, D.; Moos, M.; Ruhstaller, B. Analysis of the Emission Profile in Organic Light-Emitting Devices. Opt. Express 2010, 18, A246-A260. (S9) Perucco, B.; Reinke, N. A.; Rezzonico, D.; Knapp, E.; Harkema, S.; Ruhstaller, B. On the Exciton Profile in OLEDs-Seamless Optical and Electrical Modeling. Org. Electron. 2012, 13, S10