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1 Supporting Information Squaraine Dye for Visibly Transparent All-Organic Optical Upconversion Device with Sensitivity at 1000 nm Karen Strassel, 1,2 Adrian Kaiser, 1 Sandra Jenatsch, 3 Anna C. Véron, 1 Surendra B. Anantharaman, 1,5 Erwin Hack, 4 Matthias Diethelm, 1,5 Frank Nüesch, 1,5 Rian Aderne, 6 Cristiano Legnani, 7 Sergii Yakunin, 8 Marco Cremona, 6 and Roland Hany 1* (roland.hany@empa.ch) 1 Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Functional Polymers, CH-8600 Dübendorf, Switzerland. 2 Institute of Chemical Sciences and Engineering, Ecole Polytechnique Fédérale de Lausanne, EPFL, Station 6, CH-1015 Lausanne, Switzerland. 3 Fluxim AG, Katharina-Sulzer-Platz 2, 8400 Winterthur, Switzerland. 4 Empa, Swiss Federal Laboratories for Materials Science and Technology, Transport at Nanoscale Interfaces, CH-8600 Dübendorf, Switzerland. 5 Institute of Materials Science and Engineering, Ecole Polytechnique Fédérale de Lausanne, EPFL, Station 12, CH-1015 Lausanne, Switzerland. 6 LOEM, Optoelectronic Molecular Laboratory, Physics Department, Pontifical Catholic University of Rio de Janeiro, PUC-Rio, Rio de Janeiro, RJ, , Brazil. 7 LEO, Organic Electronics Laboratory, Physics Department, Federal University of Juiz de Fora, Juiz de Fora, MG, Brazil. 8 Laboratory of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland. S-1

2 1. EXPERIMENTAL SECTION Reactions were carried out under argon atmosphere. S1-S3 Chemicals and solvents purchased from commercial sources were used without further purification. (S1) Waumans, B.; Callant, P. Colour Laser Marking of Articles and Security Documents. Patent WO A1, (S2) Dust, M.; Neumann, P.; Hauser, P.; Wagenblast, G.; Benthack-Thoms, H.; Barzynski, H.; Schomann, K. D.; Kuppelmaier, H. Naphtholactamsquaric Acid Dyes and Optical Recording Materials Containing these Dyes. Patent US A, (S3) Véron, A. C. Near-Infrared Absorbing Cyanine Dyes and Organic-Inorganic Perovskites for Electronic Applications. University of Zürich, 2016, DOI: /uzh Synthesis of 1-Octyl-(1H)-benz[cd]indol-2-one. Benz[cd]indol-2(1H)-on (5.10 g, 30.2 mmol) was dissolved in sulfolane (20 ml) at 70 C and KI (0.99 g, 6.02 mmol, 0.20 eq) and DMAP (0.50 g, 4.06 mmol, 0.14 eq) were added. A first portion of KOH (1.01 g, 18.1 mmol, 0.6 eq) and 1-bromooctane (2.60 ml, 15.0 mmol, 0.5 eq) was then added. A second and a third portion KOH and 1-bromooctane were added after one and two hours (in total 1.8 eq KOH and 1.5 eq 1-bromooctane). After 3 hours, the reaction mixture was cooled down to room temperature (rt), diluted with ethylacetate (400 ml) and transferred to a separating funnel. The solution was washed with water and the aqueous phase was extracted with ethylacetate (3x). The combined organic phases were washed successively with a solution of 15% NaCl, 15% NaCl containing 4% HCl, 15% NaCl containing 1% NaHCO 3 and 25% NaCl. The organic phase was dried over N 2 SO 4 and the solvent was removed under reduced pressure to give g of crude intermediate product 1 as a yellow solid. Synthesis of 2-Methyl-1-octyl-benz[cd]indolium iodide. Crude compound 1 (9.23 g, 32.8 mmol) was dissolved in dry THF (30 ml) and a solution of MeMgCl (13.9 ml, 3.0 M in THF, 1.28 eq) was added dropwise over 10 min. The reaction mixture was heated to 55 C for S-2

3 60 min. After cooling to rt the reaction mixture was poured slowly into an ice/water mixture (150 ml) containing 12.3 ml of 32% HCl. THF was removed under reduced pressure, the aqueous mixture was filtered and the clear filtrate added to a stirred solution of KI (10.80 g, mmol, 2.00 eq) in water (150 ml). The red precipitate was filtered, washed with water and ethylacetate and dried under vacuum to give compound 2 as a red solid (4.60 g, mmol, 45% yield over two steps). 1 H NMR (CDCl 3 ): 8.95 (d, J=7.2, 1H), 8.59 (d, J=8.0, 1H), 8.37 (d, J=7.4, 1H), 8.26 (d, J=8.2, 1H), 8.03 (t, J=7.7, 1H), 7.87 (t, J=7.8, 1H), 4.83 (t, J=7.5, 2H), 3.44 (s, 3H), 2.00 (m, 2H), 1.46 (m, 2H), 1.31 (m, 2H), (m, 6H), 0.80 (t, J=6.9, 3H). 13 C-NMR (CDCl 3 ): 170.2, 139.2, 138.4, 135.9, 131.5, 131.1, 129.8, 128.9, 128.7, 122.6, 121.4, 48.7, 31.5, 30.4, 29.0, 28.9, 26.9, 22.4, 16.3, HR-MS (pos. ESI): m/z for [C 20 H 26 N + ]; calculated , found Synthesis of 2-[[2-Hydroxy-3-[(1-octylbenz[cd]indol-2(1H)-ylidene)methyl]-4-oxo-2- cyclobuten-1-ylidene]methyl]-1-octyl-benz[cd]indolium. Squaric acid (0.28 g, 2.46 mmol, 1.0 eq) was dissolved in a mixture of toluene (35 ml) and 1-butanol (35 ml) at 120 C. Then compound 2 (2.00 g, 4.91 mmol, 2.00 eq) was added and the reaction mixture was kept at 120 C for 2 h. The solvent was removed under reduced pressure. After recrystallization from EtOH, SQ-880 was obtained as black crystalline solid (1.08 g, 69%). 1 H NMR (CDCl 3 ): 9.20 (s-broad, 2H), 7.94 (d, J=8.0, 2H), 7.85 (t, J=7.7, 2H), 7.55 (d, J=8.2, 2H), 7.48 (t, J=7.7, 2H), 7.03 (d, J=7.1, 2H), 6.37 (s-broad, 2H), 4.17 (s-broad, 4H), 1.89 (quint, J=7.5, 4H), (m, 4H), (m, 4H), (m, 4H), 0.87 (t, J=6.8, 6H). 13 C NMR (CDCl 3 ): 183.3, 176.3, 151.1, 141.6, 131.5, 130.4, 129.7, 129.6, 128.4, 125.5, 121.6, 107.0, 92.1, 44.1, 31.7, 29.4, 29.1, 28.9, 27.2, 22.6, HR MS (pos. ESI): m/z for [C 44 H 49 N 2 O + 2 ]; calculated , found S-3

4 Figure S1-1. Cyclic voltammogram of SQ-880. Measurements and Instruments 1 H- and 13 C- NMR spectra were measured on a Bruker AV-400 spectrometer at 400 and 100 MHz. J coupling constants are reported in Hz. Abbreviations for the multiplicities are s (singlet), d (doublet), t (triplet), quint (quintet) and m (multiplet). High resolution electrospray ionization mass spectra (HR-ESI-MS) were recorded on a Bruker maxis UHPLC-HR-MS instrument. Masses are reported as m/z (mass/charge). UV-Vis-NIR spectra in solution were obtained with a Varian Cary 50 Scan spectrophotometer. A stock solution was prepared and diluted to get different concentrations for the determination of the extinction coefficient ε. The calculation of ε was performed by linear least-square fitting of plots of absorbance vs. concentration. The fits gave R2 values of Absorption and transmission spectra of thin films were measured using the same spectrophotometer. For fluorescence measurements, samples were loaded in a Horiba Jobin Yvon Fluorolog spectrometer and were excited at 808 nm with a slit width of 20 nm. The PL was recorded from 950 nm to 1600 nm for pristine squaraine and blend films. PL from a glass substrate was measured using the same experimental conditions. Film thicknesses were determined using an Ambios XP1 profilometer. Optical constants n and k for SQ-880, PCBM and the SQ-880:PCBM (1:3 w/w) blend film were S-4

5 determined by spectroscopic ellipsometry (M-2000VI, J.A. Woollam Co.) in the wavelength range of nm with three incident angles. First, the glass substrate was measured alone. Cyclic voltammetry measurements were carried out on a PGStat 30 potentiostat (Autolab) with a three cell electrode system (Au working electrode, Pt counter electrode and Ag/ AgCl reference electrode) in a 0.1 M solution of TBACl in DMF. The scan rate was 100 mv/s. Potentials were referenced to NHE by adopting a potential of V vs. NHE for Fc/Fc + in DMF and the energy level of NHE is situated 4.5 ev below the zero vacuum energy level. The half-wave potential for Fc/Fc + was 0.96 V against the reference electrode. OPDs were characterized in a N 2 -filled air-tight box covered with a glass window. Currentvoltage (J-V) characteristics were obtained using 100 mw cm -2 simulated AM1.5G solar irradiation with a calibrated solar simulator from Spectra Nova. EQE spectra were measured on a commercial setup (SpeQuest, ReRa solutions BV). The monochromatic light was chopped at 85 Hz during the measurement without additional bias light. Optionally, a voltage bias (maximum -10 V allowed) was applied during spectral response measurements. The reflection R of the OPD device was measured in an integrating sphere using a UV-Vis-NIR spectrophotometer (Shimadzu UV-3600). Internal quantum efficiency (IQE) was calculated according to IQE=EQE/A, with the absorption A=1-T-R and the transmission T was set to zero because a non-transparent device was used. S-5

6 Figure S1-2. Measurement setup for characterization of OUCs. (a) Devices were placed in a nitrogen-filled sample holder and were characterized outside the glovebox. J-V-L characteristics were measured with a Keithley 2400 and a Konica Minolta luminance meter LS-110 equipped with a close-up lens No A 980 nm wavelength laser from Thorlabs (CPS980) was used as illumination source. (b) Photo of a device in the ON-state. 2. OPTICAL EXPERIMENTS AND MODELING Optimization of the Alq 3 capping layer thickness was carried out with the thin film optics modeling software Setfos from Fluxim. Optical constants were taken from the Setfos database. S-6

$Refractive index (n) and extinction coefficient (k) for SQ-880, PCBM and the SQ-$ 880:PCBM (1:3 w/w) blend film. Figure S2-2.

on top of the Ca (2nm) / Au (8 nm) electrode.

7 Figure S2-1. Refractive index (n) and extinction coefficient (k) for SQ-880, PCBM and the SQ- 880:PCBM (1:3 w/w) blend film. Figure S2-2. The transparency of OUCs can be increased by adding an external dielectric coating on top of the Ca (2nm) / Au (8 nm) electrode. The chart shows simulated transmittance values for different thicknesses of the external Alq 3 layer. A layer thickness in the range of nm increases the transmittance values in the wavelength range nm to over 65%. S-7

8 b) Figure S2-3. (a) Experimental reflection spectrum of a blend OPD. The reflection at 970 nm is 11%. (b) shows simulated absorptions. The maximum absorption of the whole device is 0.88, in agreement with the experiment. For converting EQE to IQE, the simulated absorption (= 0.8) of the active film was considered. S-8

9 Figure S2-4. Photoluminescence spectra. The monomer emission from the pristine squaraine film is observed at 1190 nm with a vibronic shoulder. For the blend film the squaraine PL signal is strongly quenched. The small peak at 1080 nm present in both films is assigned to emission from the glass substrate. Figure S2-5. Transmittance spectra of full OUC devices with different top electrodes. S-9

3. BILAYER OPD and OUC Figure S3-1: Schematic drawings of the bilayer photodetector (left) and upconverter (right).

22-39 nm thick SQ-880 layers were coated from CHCl 3 onto a 40 nm thick layer of C 60 that was photopolymerized before dye coating to prevent dissolution.

8 ma cm -2 and fill factors (FF) decreased from 45% to 37%. For dye thicknesses below 30 nm, however, on average 4 out of 8 cells per device were shorted, probably due to incomplete film formation.

10 3. BILAYER OPD and OUC Figure S3-1: Schematic drawings of the bilayer photodetector (left) and upconverter (right). The NIR-sensitive photodetector was also tested in a bilayer SQ-880/C 60 configuration nm thick SQ-880 layers were coated from CHCl 3 onto a 40 nm thick layer of C 60 that was photopolymerized before dye coating to prevent dissolution. S4 When increasing the dye layer from 22 nm to 28 nm, open-circuit values V oc = (0.22 ± 0.04) V were constant, short-circuit currents (J sc ) increased from 2.5 ma cm -2 to 3.8 ma cm -2 and fill factors (FF) decreased from 45% to 37%. For dye thicknesses below 30 nm, however, on average 4 out of 8 cells per device were shorted, probably due to incomplete film formation. For thicker dye films the device reproducibility (to 75%) and V oc values (to 0.27 V) increased, whereas J sc and FF dropped continuously to 2 ma cm -2 and 25%, respectively. The best performing solar cell consisted of a 33 nm thick SQ-880 layer (Figure S3-2). For the bilayer SQ-880/C 60 configuration, the EQE at 980 nm increased however marginally from 4.8% at 0 V to 7.3% at -2 V, much less than what we observed for the bulk heterojunction photodetector. S-10

11 -70 Current density (ma/cm 2 ) V oc = 0.25 V J sc = 3.91 ma/cm 2 FF = 40.37% PCE = 0.39% EQE (%) V 0.1 V 0.5 V 1 V 2 V 0 10 Dark Light Voltage (V) Wavelength (nm) Figure S3-2. (left) Best J-V scan of a bilayer OPD (SQ-880 layer = 33 nm, 100 mw cm -2 AM1.5G solar radiation) and (right) EQE as function of the applied voltage bias. The low EQE values of the bilayer photodetector limit the hole supply to the OLED which directly translated into a lower performance of the corresponding OUCs (Figure S3-3). Device turn-on was again observed at 3 V but the current density (2.7 ma cm -2 ) and luminance (62 cd m -2 ) at 12 V were lower than for the bulk OUCs. Because the EQE shows a small dependence on the voltage bias, current and luminance values approach a plateau for voltages above ~6 V. Figure S3-3. Characteristics of bilayer OUCs. Luminance (left), current (right) and corresponding on/off ratios. S-11

12 (S4) Zhang, H.; Borgschulte, A.; Castro, F. A.; Crockett, R.; Deniz, O.; Heier, J.; Jenatsch, S.; Nüesch, F.; Sanchez-Sanchez, C.; Zoladek-Lemanczyk, A.; Hany, R. Photochemical Transformations in Fullerene and Molybdenum Oxide Affect the Stability of Bilayer Organic Solar Cells. Adv. Energy Mater. 2015, 5, FABRICATION OF BLEND OUCs Before layer deposition, patterned ITO substrates (~12 Ohms square -1 ) were cleaned successively in acetone, ethanol, a 2 vol% aqueous solution of Hellmanex (5 min each step) and finally three times 5 min in deionized water using an ultrasonic bath. For the preparation of the TiO 2 solution, HCl (conc., 30 µl), H 2 O (135 µl) and ethanol (10 ml) were stirred in a round bottom flask. In a second round bottom flask titanium(iv)isopropoxide (0.95 g) was cooled to 0 C and ethanol (10 ml) was added while stirring. Afterwards the first solution containing HCl, H 2 O and ethanol was added dropwise while stirring at 0 C. After complete addition the solution was stirred for another 30 min at 0 C. To obtain a 35 nm thick film of TiO 2, the solution was spin coated on the ITO substrate using the spin coating parameters: step 1, time 5 s, acceleration 300 rpm/s, final speed 1000 rpm; step 2, time 60 s, acceleration 3000 rpm/s, final speed 4000 rpm. After spin coating the substrates were placed in an oven and heated to 460 C over a time period of 3 h, kept at 460 C for 2 h and then cooled down to room temperature. Before deposition of further layers, the TiO 2 substrates were heated at 120 C for 10 min inside a glove box. The SQ-880:PCBM blend was deposited from a filtered solution in CHCl 3 in the glove box. For a (72 ± 5) nm thick blend layer with a ratio of 1:3, 2.5 mg SQ-880 and 7.5 mg PCBM were dissolved in 1 ml of CHCl 3 and spin coated: 60 sec, acceleration 3000 rpm/s, final spin speed 4000 rpm. Further layers (Alq 3 (evaporation rate Å s -1 ), MoO 3 S-12

13 ( Å s -1 ), TPD ( Å s -1 ), Ag ( Å s -1 ), Al (0.2-1 Å s -1 ), Au ( Å s -1 ), and Ca (0.1 Å s -1 )) were deposited via thermal evaporation at a pressure below 5 x 10-6 mbar. Table S1. Average OUC performance data. Device active area was 3.1 or 7.1 mm 2. Top electrode N cells Turn on, J at 12 V J on/off L at 12 V L on/off tested 1 cd m -2 (ma cm -2 ) (cd m -2 ) (V) 10 nm Ca / 100 nm Al 2 nm Ca / 12 nm Ag / ± ± 110 at 4 V ± ± 25 at 4 V 328 ± ±75 at 5 V 385 ± ± 20 at 4.5 V 20 nm Alq 3 2 nm Ca / 8 nm Au / ± ± 89 at 3 V 305 ± ± 85 at 3.5 V 20 nm Alq 3 2 nm Ca / 8 nm Au / ± ± 35 at 3.5 V 140 ± ± 18 at 4 V 55 nm Alq 3 5. CALCULATION OF THE PHOTON-TO-PHOTON CONVERSION EFFICIENCY (P2PCE) The P2PCE is given by the ratio of the number of visible light photons emitted to the number of incident NIR photons and was calculated using the following equation P2PCE = number of vis. photons emitted number of incident NIR photons = I S(λ)λ 0 h dλ λ NIR P NIR h S-13

14 where the factor π results from the assumption that the OLED behaves like a Lambertian emitter, I 0 is the radiance, S(λ) the electroluminescence (EL) spectrum which was normalized so that the area of the integral is equal to one, λ the wavelength of the extracted photons, h and c are the Planck constant and the speed of light, λ NIR is the wavelength of the incident NIR laser and P NIR is the incident NIR power density. We measured the EL spectrum for our measurement setup where the emitted light passes first through the photodetector layer. The shape of the curve differs slightly from the shape of the pure Alq 3 EL spectrum as a small fraction of the emitted light is absorbed by the SQ-880:PCBM layer (Figure 5 main text). We used the corrected shape of the EL spectrum but did not consider this absorption loss in the efficiency calculation. The radiance I 0 was calculated using the equation = 683 where L is the NIR induced luminance in cd/m 2, corresponding to the luminance under NIR illumination subtracted by the luminance in the dark. As 10% of the emitted light is reflected at the glass window of the sample holder and does not reach the detector, the value obtained from the luminance meter was multiplied with 1.1. Using the NIR induced luminance L, which is given in the photometric unit cd/m 2, the radiance I 0, which is described by the radiometric unit W/(m 2 Ω) was calculated. For this the value of L was divided by the integral of the product of the photopic response g(λ) curve normalized to the peak value of 683 lm/w and the corrected and normalized EL spectrum S(λ). As NIR source we used a laser with a wavelength of 980 nm and a total power of 4.5 mw. The laser beam has an elliptic form with semi-major axis lengths of 0.2 cm and 0.1 cm. To determine the effective NIR input power on the sample we considered (i) that ~ 10% of the in- S-14

15 cident light is reflected at the top cover glass of the sample holder and (ii) that the NIR laser hits the sample under an angle α of ~40 o which increases the illuminated area by a factor of (1/cos(α)). The effective power P NIR reaching the sample under these assumptions is 494 W/m 2. To obtain the number of incident NIR photons, the NIR input power of the laser has to be divided by the energy of one photon at 980 nm. S-15

Supporting Information

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,