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Copyright WILEY VCH Verlag GmbH & Co. KGaA, 69469 Weinheim, Germany, 2015. Supporting Information for Adv.

201501065 Water Ingress in Encapsulated Inverted Organic Solar Cells: Correlating Infrared Imaging and Photovoltaic

1 Copyright WILEY VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, Supporting Information for Adv. Energy Mater., DOI: /aenm Water Ingress in Encapsulated Inverted Organic Solar Cells: Correlating Infrared Imaging and Photovoltaic Performance Jens Adams,* Michael Salvador, Luca Lucera, Stefan Langner, George D. Spyropoulos, Frank W. Fecher, Monika M. Voigt, Simon A. Dowland, Andres Osvet, Hans-Joachim Egelhaaf, and Christoph J. Brabec

2 ((Supporting Information can be included here using this template)) Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany, Supporting Information Title Water ingress in encapsulated inverted organic solar cells: correlating infrared imaging and photovoltaic performance Jens Adams 1a*, Michael Salvador 2,3a, Luca Lucera 1, Stefan Langner 2, George Spyropoulos 1, Frank W. Fecher 1, Simon A. Dowland 4, Andres Osvet 2, Hans-Joachim Egelhaaf 1, Monika M. Voigt 1,2 and Christoph J. Brabec 1,2 IR imaging: We carried out electroluminescence (EL) and infrared (IR) imaging based on ELLI, DLIT, ILIT as well as PL imaging. For ELLI and DLIT measurements, two Equus 327k NM IR cameras (IRCAM GmbH, Erlangen, Germany) equipped with different types of detectors were used (Figure S1). The IR-camera used for DLIT investigations was equipped with a cooled indium-antimonite (InSb) based focal plane array (FPA) detector (640 x 512). The InSb detector is highly responsive in the spectral range 1.5 µm 5 µm and has a noise equivalent temperature difference of less than 20 mk. For ELLI, we employed a cooled indium-gallium-arsenide (InGaAs) FPA detector (640x512) with an optimum spectral response between 0.8 µm and 1.7 µm. Both cameras were run at a frame rate of 100 Hz and were controlled with a computer for real-time lock-in calculations. The cameras were equipped with a 25 mm focal lens imaging system featuring a spectral transparency >90% (IRCAM GmbH, Erlangen, Germany). 1

Figure S1: Schematic illustration of the lock-in setup used for ELLI, DLIT and ILIT investigations (See experimental methods and SI (IR-Imaging) for details).

3 Figure S1: Schematic illustration of the lock-in setup used for ELLI, DLIT and ILIT investigations (See experimental methods and SI (IR-Imaging) for details). Interpretation of signals from IR imaging: For the sake of clarity, it is worth noticing that the detected EL or IR radiation is strongly related to the current being injected, the quality of the active layer, and the quality of the active layer/electrode interface. During an ELLI or DLIT measurement, an amplitudemodulated current is injected into the cell, causing radiative and non-radiative recombination processes of charge carriers. In both cases, the reverse functionality of the device is tested and the solar cell typically emits EL radiation (0.8µm - 2µm) and heat. Because DLIT and ELLI are based on injection current, no discrimination between electrode degradation and active layer degradation can be made. One way to overcome this limitation is to characterize the PL emission of the active layer. In this case, the device is continuously excited with monochromatic light while maintained under open circuit. As long as no load is applied to the cell, lateral current flow can be neglected and the detected PL emission originates directly from radiative recombination processes inside the active layer [62,76]. 2

4 Calcium deposition: Calcium was deposited by thermal evaporation on glass substrates (25 mm x 25 mm x 1.3 mm) similar to those used for solar cell fabrication. Thermal evaporation of calcium films with a thickness of 100 nm was preformed inside a glove box under nitrogen atmosphere. After evaporation, the samples were encapsulated using a glass barrier with a thickness of 0.7 mm and an ultra violet curable epoxy adhesive from DELO (Katiobond LP 655; full encapsulation). Table 1: Parameters used to calculate D from Eq 5 of the main text. Data Saturation concentration of adhesive c s Value mol/cm³ (65 C/ 85%RH) Saturation concentration of adhesive c s mol/cm³ (60 C/ 90%RH) dx/d t m/ s Diffusion constant calculated by using Fick s 1 st law of diffusion: In addition to using Fick s 2 nd law of diffusion, as elaborated in the main text, we calculated the diffusion constant D of water in the adhesive by applying Fick s 1 st law, which can be written as J = D, Eq. S1 3

5 where J (mol m -2 s -1 ) is the diffusion flux of moisture, D (m 2 /s) is the diffusion coefficient, and Δc is the concentration difference between saturation concentration c s and actual concentration c 0 across the adhesive of thickness l. The diffusion coefficient reflects the speed at which the moisture diffuses through the adhesive of our sample. It can be written by rearranging Eq S1: D = ( ), Eq. S2 For the diffusion flux of moisture through the adhesive (DELO Katiobond LP655) we used the water vapor transmission rate (WVTR = 6.1 g m -2 d -1 at 60 C/90%RH) as provided by the technical data sheet. The saturation concentration c s was measured gravimetrically to be mol/cm³. The thickness of our adhesive film was measured to be 15 µm (cell stack ~150 nm). Using these input parameters Eq. S2 gives rise to D 0 = m 2 s -1. The calculated diffusion constant refers to water diffusion through the adhesive at 60 C and a relative humidity of 90%. For our test conditions (65 C/85%RH) D 0 needs to be corrected. We use the determined E a for the diffusion process and a modification of Eq. S1. In this case D is defined as D = D exp. Eq. S3 and can be calculated to D = m 2 s -1, which is in close agreement to the value reported in the main text. 4

6 Figure S2: Represntative j-v characteristic of one test cell. The table shows average values for Jsc, FF, Voc, PCE for 10 test devices at t = 0 h. Figure S3: dark j-v characteristics of the sample presented in Figure 3 of the main text. 5

For estimating the accelerated lifetime, we applied a linear fit to the data points and extended the fit to 80% of

7 Figure S4: Extrapolated shelf life of inverted P3HT:PCBM solar cells. Each data point represents an average value of 10 devices. For estimating the accelerated lifetime, we applied a linear fit to the data points and extended the fit to 80% of the initial value (T80) for 7 C (red line) and 20 C (black line) storage temperature. Figure S5: ELLI line scans (top to bottom) of the solar cell shown in Figure 6 as a function of the storage time at 65 C/85%RH. 6

The differences in contrast when compared to the measurements presented in Figure 6 arise from a larger distance between

8 Figure S6: ELLI images of fresh and aged devices measured using 1 V forward bias. The solar cells were kept in the dark at 65 C/85%RH. The differences in contrast when compared to the measurements presented in Figure 6 arise from a larger distance between sample and camera during the ELLI measurements. Figure S7: Spatial distribution of PL signal of a fresh (left) and degraded (right) solar cell presented in Figure 8. The PL image does not follow the same degradation motif as ELLI. 7

9 Figure S8: Normalized PL and EL spectra of an encapsulated and inverted P3HT:PCBM solar cell. For the excitation of PL we used an argon ion laser beam with a wavelength of 488 nm. EL radiation was measured with an injection current of 48 ma/cm². Figure S9: Active cell area vs. photovoltaic cell parameters. The device performance and ELLI image used for the analysis were extracted from the left bottom solar cell shown in Figure S6. 8

Figure S10: Water diffusion kinetics through a packaged calcium test and an OPV

For both experiments the samples were stored in dark at 65 C/85%.

Figure S11: Images of encapsulated calcium electrodes with a thickness of 100 nm.

10 Figure S10: Water diffusion kinetics through a packaged calcium test and an OPV device with an active are of 1.44 cm². For both experiments the samples were stored in dark at 65 C/85%. The red square represents the dimensions of the active OPV area. Figure S11: Images of encapsulated calcium electrodes with a thickness of 100 nm. The encapsulation packaging was performed the same way as for the OPV devices. The sample was stored in a climatic chamber at 65 C/85%RH and periodically photographed. 9

Figure S12: Experimentally determined kinetics of water diffusion in epoxy adhesive using calcium test (Figure S10): penetration distance vs. t 1/2.

11 Figure S12: Experimentally determined kinetics of water diffusion in epoxy adhesive using calcium test (Figure S10): penetration distance vs. t 1/2. The error bars represnt approximated reading errors. The slope dx/d t is dx/d t = m/ s. Figure S13: Temporal evolution of solar cell parameters of an encapsulated and inverted P3HT:PCBM solar cell with silver grid finger electrodes. The cell was stored under controlled moisture and temperature settings at 65 C/85% RH. The cell was investigated using ELLI 10

with a pulsed injection current of 80 ma, a lock in

Figure S14: (left) ELLI image of a fresh OPV device with a

(right) Line scans of local ELLI emission of a fresh and

Both ELLI images were measured with an injection current of

12 with a pulsed injection current of 80 ma, a lock in frequency of 1 Hz, and an acquisition time of 60 s. Figure S14: (left) ELLI image of a fresh OPV device with a grid finger electrode. (right) Line scans of local ELLI emission of a fresh and aged device. Both ELLI images were measured with an injection current of 80 ma. The increased ELLI emission of the aged OPV device can be attributed to an increased current density in the active area (see explanation in the main text). 11

Figure S15: (left) ELLI image of an aged OPV device with a grid finger electrode. The solid and dashed lines refer to line scans presented in the right graph.

Degradation occurs with approximately the same kinetics between and under the grid fingers.

13 Figure S15: (left) ELLI image of an aged OPV device with a grid finger electrode. The solid and dashed lines refer to line scans presented in the right graph. (right) Line scans of local ELLI emission. The ELLI image was measured with an injection current of 80 ma. Degradation occurs with approximately the same kinetics between and under the grid fingers. Figure S16: ELLI images of encapsulated and inverted P3HT:PCBM solar cells with silver electrodes of different thickness measured after different degradation stages. The samples were stored under controlled temperature and moisture settings at 85 C/85%RH. Each sample was investigated with a lock in frequency of 1 Hz, acquisition time of 15 s, and an injection current of 10 ma 12

14 Jsc Voc 2 J SC V OC 0.2 before DH after DH AL DH Conditions (DH= 85 C, 85% RH Damp Heat) PCE FF 1 PCE FF before DH after DH AL DH Conditions (DH= 85 C, 85% RH Damp Heat) 0.2 Current Density [ma/cm2] Complete device before 85/85 after 85/85 (2hrs) Incomplete device 85/85 after AL (2hrs) Bias [V] 13

15 Figure S17: Degradation of full (ITO/ZnO/P3HT:PCBM/PEDOT:PSS/Ag) and partial (AL: ITO/ZnO/P3HT:PCBM) devices under damp heat (DH: 85 C/85%RH). Full devices were measured before and after DH. Partial devices were finalized and measured after exposure to DH. a) b) Extinction h 4 h 24 h 70 h 118 h P3HT:PCBM 0.2 Extinction h 4 h 24 h 70 h 118 h Wavelength (nm) P3HT:PCBM/PEDOT:PSS Wavelength (nm) Figure S18: UV-VIS absorption spectra as a function of aging time for P3HT:PCBM films (a) and P3HT:PCBM films overcoated with PEDOT:PSS (b). The samples were stored in a climate chamber in the dark under 65 C/65%RH. The blend films were doctor-bladed on top of Al:ZnO coated glass. ((Please insert your Supporting Information text/figures here. Please note: Supporting Display items, should be referred to as Figure S1, Equation S2, etc., in the main text ) 14

Characterization using laser-based technique for failure Si PV module

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