Supporting Information. for. Removing Leakage and Surface Recombination in Planar Perovskite Solar Cells

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1 Supporting Information for Removing Leakage and Surface Recombination in Planar Perovskite Solar Cells Kristofer Tvingstedt 1 *, Lidón Gil-Escrig 2, Cristina Momblona 2, Philipp Rieder 1, David Kiermasch 1, Michele Sessolo 2, Andreas Baumann 3, Henk J. Bolink 3 and Vladimir Dyakonov 1,3 1 Experimental Physics VI, University of Würzburg, Würzburg, Germany 2 Instituto de Ciencia Molecular, Universidad de Valencia, Paterna, Spain 3 Bavarian Center for Applied Energy Research Würzburg, Germany 1. Experimental Section The three sets of devices were manufactured as follows; photolithographically patterned indium tin oxide (ITO) coated glass substrates were purchased from Naranjo-substrates and PEDOT:PSS (Clevios TM P VP AI 4083) was obtained from Heraeus. polytpd was purchased from ADS Dye Source. PbI 2 was purchased from Sigma Aldrich and CH 3 NH 3 I from Lumtec, all of them were used as received. The IPH fullerene was purchased from Solenne BV. The ITO-coated glass substrates were first cleaned with soap, water and isopropanol in an ultrasonic bath, followed by O 2 plasma treatment. The first set of devices (type A) comprised PEDOT:PSS spin-coated on top of ITO and annealed at 150º for 15 min. For our second set of devices (type B) a thin film of polytpd was deposited from a chlorobenzene solution (7 mgml -1 ) on top of the PEDOT:PSS layer whereas our third set (type C) only comprised the polytpd film alone, directly deposited on the ITO. The polytpd layers were annealed for 180 C for 30 mins. The substrates were then transferred to a vacuum chamber integrated in a nitrogen-filled glovebox (O 2 < 0.1 ppm and H 2 O < 0.1 ppm) and evacuated to a pressure of 10-6 mbar. Two ceramic crucibles were filled with

2 CH 3 NH 3 I and PbI 2 and heated to 70 ºC and 250 ºC, respectively. The film thickness was controlled by the PbI 2 sublimation at a rate of 0.5 As -1. The fullerene layer was deposited by spin coating from chlorobenzene solution (20 mgml -1 ) in air. The devices were completed by the thermal evaporation of the top electrode under a base pressure of mbar to a thickness of 100 nm of Ag or Ba/Ag (10/100 nm). Table 1 describes the mean value and the standard deviation of the photovoltaic parameters of the 16 cells for each set as measured upon manufacturing in Valencia as well as after the entire study was conducted in Würzburg. The PEDOT:PSS cells does show noticeable degradation, whereas the polytbd containing cells were confirmed to be quite stable. TABLE S1 HTL PCE [%] FF [%] V OC [V] J SC [ma/cm 2 ] ptpd fresh 10.93±0.5 59± ± ±0.15 ptpd after 8.9± ± ± ±0.6 PEDOT+pTPD fresh 8.46± ± ± ±0.18 PEDOT+pTPD after 8.33± ±1 1.09± ±0.4 PEDOT:PSS fresh 1.31± ± ± ±0.16 PEDOT:PSS after 0.58± ± ± ±0.44 A spectrally stable cold LED in combination with 6 Thorlabs ND filters was used to generate ~60 different light intensities, spaced in even logarithmic steps, for sampling of sufficient data for the full V OC (suns) relation. A Keithley 6430 remote source measure unit (SMU) was employed to determine the stabilized V OC averaged for 20 seconds, after a prior filter/cell burn in time of 30 seconds. The same LED was used to simulate the illumination intensity of the three familiar light sources for the illuminated J-V curves. The OCVD measurements were conducted by illuminating the cells with the LED for 5 seconds, to rapidly switch it off employing a home built

3 electrical switch and an Agilent function generator. The voltage decay of the solar cells over a 1 GΩ input impedance amplifier was monitored by an Agilent Infinium 90254A digital storage oscilloscope for the time range between 0.1 µs and ~100 ms. For time ranges longer than 100 ms we instead employed an Agilent 4155C parameter analyzer with a built in impedance of as high as 10 TΩ. The high load of the measurement instrumentation is crucial, as it will have the same effect as having a leaky shunt path in parallel. Accordingly, if one intends to monitor the decay of the cell, as opposed to over the employed measurement load, the load needs to be as high as possible. 1. Surface coverage. All devices were studied with optical and scanning electron beam microscopy, after the top electrode was removed by a careful scotch tape delamination procedure. Figure S1 displays SEM images that show that the structure and coverage of the perovskite films are identical on both the micro and the macro scale. We can therefore confirm that the simultaneous manufacturing by the dual evaporation process does indeed form extremely uniform as well as with similar micro-structure over large areas; unlike solution processing would be able to achieve. This, together with the statistical reproducibility of our observations, allows us to rule out that one device should possess a higher density of structural pinhole formation in the actual perovskite layer. The leaky behavior of the PEDOT based cell can hence not be ascribed to this. The optical microscope images of S2 however reveal micro sized (30-100µm) discolorations underneath the perovskite film, as mentioned in the main text.

4 Figure S1. SEM images of the actual measured and presented devices in the manuscript after the top electrode has been removed by scotch tape delamination. Images are taken with (upper three) and 1000 (lower three) times magnification. Figure S2. Optical images taken with 10 times magnification after the SEM imaging was performed (SEM imaging obviously permanently affects the perovskite layer). The cell (middle) based on both PEDOT and poly TPD however displays additional discolorations not seen in the other cells based on only one single organic layer.

5 2. RC and diode-capacitor fitting Equation 2 and 3 of the main manuscript describes the temporal voltage decay of a capacitor in parallel with either a resistor (shunt) or a diode, respectively. In both equations, there is accordingly only the capacitance which is free to be used as a fit parameter. All other values in the two equations are already determined by the steady state measurements. The slope of the linear part of the decay is for example determined by the ideality factors presented in figure 4b. The voltage decay in figure 3 can be nicely described by the equivalent circuit and the two equations for three out of the four cells studied. The unclear transition from diode dominated to shunt dominated behavior of cell B however makes the simple fitting less straightforward for this device. We emphasize that the low starting voltages V(t=0) of the decay is due to the lower illumination intensity (corresponding to room-light) used here. A slight increase of the ideality factor (towards exactly 2!) is also needed for the lower voltage regime of the polytpd cell, which simply indicates that the dominant recombination mechanism is indeed depending on the carrier density. The resulting capacitances for the three cells in figure S3 amount to 53, 16 and 1.5 nf for cell A, cell C and the Si cell, respectively.

6 V OC / V A (Pedot) C (p-tpd) Si ref Si ref MOhm Diode Cap. fitting (Eqn. 2) RC fitting (Eqn. 3) Time (s) Figure S3.Fitting of the OCVD traces of figure 3 in the main text with eqn 2. and eqn.3 describing the R-C and diode-capacitor behavior as a function of time. 3. Low light intensity response The significantly different spectral distribution between sunlight and many commonly employed indoor lighting sources such as fluorescent tubes imply that, although they may appear bright to the sensitivity region of the human eye, the actual rate of photons is commonly more than three orders of magnitudes lower than full spectral sunlight. To illustrate this, Figure S4 displays the absolute photon flux distribution of sunlight (AM 1.5 NREL ASTM G173-03), two indoor light sources mounted in our lab ceiling (at a distance of ~1.5 m) and that of moonlight at night, in the wavelength range between 300 and 1100 nm. This last selected reference exemplifies a very low intensity light source, whose irradiance (of the almost full moon) in November 30 (2012) was provided in the work by Cramer. S1 The measured integrated number of photons from the incandescent light tube is 1825 times lower than that of sunlight whereas the total (provided 380-

7 1080 nm range) integrated Cramer lunar photon flux is times weaker. However, the spectral part that the perovskite cells actually see is just 920 times lower than sunlight for the fluorescent tube and times lower for moonlight. Photon Flux / m -2 s -1 nm AM 1.5 Solar Flux 60W Light bulb in Ceiling Fluorescent Tube in Ceiling Full Moon (Cramer) Photodet. EQE Perovskite EQE Wavelength / nm EQE Figure S4. Spectral distribution of absolute photon flux of four common light sources plotted together with the EQE of a Si photodetector and a representative polytpd based perovskite (device type C) cell. Illuminating the cells with the intensities corresponding to the specified familiar light sources as presented in Figure S4 leads to the J-V curves in Figure S5. Device A, with only PEDOT:PSS, qualifies barely for indoor applications, and the small hysteresis renders in addition some uncertainties in terms of the representative characteristics. However, a stable and high V OC of around 830 mv is obtained under the same conditions for type B and C cells, both containing polytpd layers, both making them suited for indoor use. When the spectral distribution of the weak moonlight photon flux in Figure S4 is convoluted with the external quantum efficiency

8 EQE(λ) of Device C (employing only polytpd), a moonlight photocurrent of merely Am -2 is obtained. This photocurrent, times weaker than the 155 Am -2 of sunlight, can of course not be utilized for meaningful conversion into any useful electrical power amount, but nonetheless clearly highlights the pronounced outcome of the removal of the shunt recombination mechanism. The PEDOT:PSS based devices (type A and B) show, as expected, a negligible open circuit voltage (and power conversion efficiency) in this weak photon flux, whereas device C is able to retain an impressive open circuit voltage of 530 mv (and a corresponding power conversion efficiency of 7.4% having assumed the spectra of Ref. S1 to embody the full power distribution of moonlight). J / Am -2 J / Am FF=0.44 / 0.48 FF=0.43 / 0.45 FF=0.36 PEDOT:PSS Sun fresh in Val. Sun in Würz. Roomlight Moonlight Dark Voltage (V) 10 2 FF= FF= FF= FF=0.73 polytpd Sun Fresh in Val. Sun in Würz. Roomlight Moonlight Dark Voltage (V) J / Am -2 J / Am Voltage (V) 10 2 FF= FF= Voltage / V Figure S5. Illuminated and dark absolute J-V curves highlighting the photocurrent and corresponding photovoltage originating from the three familiar light sources for devices A, B, C and the Si-photodetector. Fill factor values are inset in the graphs showing the effect of increased series resistance at higher currents. Device C is the only device able to retain a respectable photovoltage from moonlight intensities, only due to the elimination of the shunt FF=0.68 FF=0.70 FF=0.52 FF=0.55 PEDOT:PSS / polytpd Sun Fresh in Val. Sun in Würz. Roomlight Moonlight Dark Hamamatsu Si photo detector Sun Roomlight Moonlight Dark

9 The moonlight photovoltage of device C outperforms also the 210 mv of the monocrystalline Si photodetector substantially, although this is mainly assigned to the higher bandgap (and lower J 0 ) of the perovskite, and should therefore not solely be attributed to the actual shunt removal. The Si photodetector does also not display any pronounced leakage current contribution at all. This is however again mostly due to the different bandgap of the Si and the perovskite, which provides the Si photodetector with a substantially higher dark saturation current (J 0 ). Hence, any leakage current over the stated 100 GΩ shunt would always be smaller than the exponential part of the diode current, even for low voltages, as the starting point of the diode curve, J 0 lies as high as 52 nam -2.To elaborate more on the observed V OC in the dark of device C we in Figure S6 include double sweeps I-Vs with various ending voltages, clearly displaying a strong correlation between end voltage/current value and the resulting V OC in the dark of the succeeding reverse sweep. This is an indication of more pronounced charging of the electrode layers the more forward current was running through them. The inset also displays the expected rate dependence of the V OC in the dark, with indeed lower values the slower the voltage sweep. I(A) End values. 1.3V 0.85V 0.6V 0.4V 0.2V V Voltage (V) I(A) Sweep Speed 5mV/s 10mv/s

10 Figure S6. Double sweep I-Vs of the polytpd based device (C) with different end values of voltage and different sweep rates. References: S1 C. E. Cramer, K. R. Lykke, J. T. Woodward, A. W. Smith, J. Res. Natl. Inst. Stan. 2013, 118, 396.