The Role of the Selective Contacts in the Performance of Lead Halide Perovskite Solar Cells

Transcription

1 SUPPORTING INFORMATION The Role of the Selective Contacts in the Performance of Lead Halide Perovskite Solar Cells Emilio J. Juarez-Perez, 1 Michael Wuβler, 1, 2 Francisco Fabregat-Santiago, 1 Kerstin Lakus-Wollny, 2 Eric Mankel, 2 Thomas Mayer, 2 Wolfram Jaegermann, 2 and Ivan Mora-Sero *,1 1 Photovoltaics and Optoelectronic Devices Group, Departament de Fisica, Universitat Jaume I, Castello, Spain. 2 Institute of Materials Science, Technische Universita t Darmstadt, D Darmstadt, Germany. *corresponding author: sero@uji.es. SI1.- Experimental methods: Device preparation and nomenclature The abbreviation used for the designation of a complete device is EPH. The character "E" means that the device has a selective layer for the electrons, "P" refers to a mesoporous layer of nanoparticles with the embedded (CH 3 NH 3 )PbI 3 perovskite and "H" refers to the hole selective layer of spiro-ometad. In this paper 6 types of devices are introduced, three full devices (EPH) where the composition of the compact layer "E" can be TiO 2, CdS or ZnO and three incomplete cells, EP, PH and P corresponding to one device without spiro-ometad layer, without TiO 2 compact layer and without both layers, respectively. Next, the experimental conditions for the device preparation is segmented by stages and used as appropriate to assemble every device. A general considerations has been that the perovskite deposition in the device was carried out in a globe box under nitrogen atmospheric conditions and a humidity of <0.5 ppm and the spiro-ometad layer deposition was carried out at room humidity and oxygen conditions. Cleaning and pretreatments for the substrates FTO-coated glass substrates (Tec15, Pilkington) were etched with zinc powder and HCl (2 M) to obtain cm 2 of active electrode area per pixel. The sheets were then washed with soap (Hellmanex), de-ionized water and ethanol. After that, the substrates were cleaned by ultrasonication in an acetone:isopropanol 0.5:0.5 (v/v) solution, rinsed

2 with de-ionized water and ethanol, dried and finally treated with an O 3 /ultraviolet process during 15 min. TiO 2 Compact Layer A TiO 2 compact layer was deposited on the clean sheets by aerosol spray pyrolysis at 500 ºC using 40 ml of a titanium diisopropoxide bis(acetylacetonate) solution (75% in 2-propanol, Sigma-Aldrich) diluted in ethanol (1:39, v/v) and oxygen as carrier gas. After cooling to room temperature, the sheets were kept for the next steps. ZnO Compact Layer The ZnO compact layer was deposited as it is described in the reference 1. An undoped ZnO compact layer was deposited on the clean sheets by spin coating (1000 rpm, 30 seconds) a 100 µl portion of a zinc acetate dihydrate solution in methanol (0.25 M). After drying at 100 ºC during 15 minutes, the ZnO films were gradually heated to 500 ºC for 1 hour and cooled to room temperature. CdS Compact Layer A 90 nm thick layer of CdS layer was sputtered onto FTO substrates under a pressure of mbar and 300 C of temperature. The used magnetron cathode (Ion X-2 UHV / Thin Film Consulting) has a power of 16 W. A flow of 10 standard cubic centimeters per minute of argon was used as sputter atoms towards a CdS target with a purity of 99,99 % (Testbourne Ltd.) The distance between the substrate and the target was 7 cm. The deposition rate was 5-6 nm/min and a mask was used to get a CdS-free area for the working electrode. Mesoporous TiO 2 layer The mesoporous TiO 2 layer was deposited by spin coating at 5000 rpm. during 30 s using a TiO 2 paste (Dyesol 18NRT, 20 nm average particle size) diluted in terpineol (1:3, weight ratio). After drying at 80 ºC, the TiO 2 layers were heated to 470 ºC at this temperature for 15 min and cooled to room temperature. The thickness determined by Scanning Electron Microscopy was ~400 nm. Mesoporous Al 2 O 3 layer The mesoporous Al 2 O 3 layer was deposited by spin coating at 2500 rpm. during 60 s using a colloidal dispersion of < 50 nm Al 2 O 3 nanoparticles in isopropanol, followed by drying process at 150 C during 30 minutes. Iodide perovskite deposition on TiO 2 mesoporous layer The CH 3 NH 3 PbI 3 halide perovskite was deposited using the two-step sequential deposition method. 2 PbI 2 was dissolved in N,N-dimethylformamide at a concentration of 33 % (w/w) stirring at 80 ºC and keeping it at 80 ºC during the whole procedure. The

3 mesoporous layer was then spin-coated with the PbI 2 solution at 6500 r.p.m. during 90 s and dried at 80 ºC for 30 min. After cooling to room temperature, the films were dipped in a solution of CH 3 NH 3 I in 2-propanol (10mg/ml ) for 30 s, rinsed with 2-propanol and dried at 80 ºC during 30 min. Iodide perovskite deposition on CdS substrates As the CdS compact layer is not stable at the temperature needed for the sintering of a mesoporous TiO 2 layer, a low temperature deposition Al 2 O 3 mesoporous layer process (see above) was chosen to assemble the scaffold for the perovskite layer. The active area of these substrates were 1.5 cm² and the perovskite deposition method used is the same as described above for a mesoporous TiO 2 layer. Hole transport layer deposition The HTM was deposited by spin coating at 4000 r.p.m. for 30 s outside of the glovebox. The HTM recipe was prepared dissolving 72.3 mg (2,29,7,79-tetrakis(N, N-di-pmethoxyphenylamine)-9,9-spirobifluorene) (spiro-meotad), 28.8 µl of 4-tertbutylpyridine and 17.5 µl of a stock solution of 520 mg/ml lithium bis(trifluoromethylsulphonyl)imide in acetonitrile in 1 ml of chlorobenzene. Gold electrode deposition 60 nm of gold was thermally evaporated to pattern the device electrodes using a commercial MBraun vacuum chamber. The substrates were placed at a distance of 25 cm from the top of the evaporation source. A shutter is placed below the substrate holder and a quartz microbalance sensor is monitoring the rate of gold evaporation, before to beginning the evaporation process the chamber was evacuated until pressure of mbar. Devices characterization J-V curves were performed under 1 sun illumination, AM mwcm -2 simulated sunlight (ABET Technologies, 1000W Xe light source) previously calibrated with an NREL-calibrated Si solar cell. The measurements were performed without mask, and consequently efficiencies are overestimated in a ~10%. Impedance spectroscopy measurements were carried out by means of a FRA equipped PGSTAT-30 from Autolab under 1 sun light illumination conditions at different forward voltage bias and applying a 20mV voltage perturbation over the constant applied bias with the frequency ranging between 1 MHz and 0.01 Hz.

4 SI2.- Reproducibility: Table SI2: Statistical solar cell parameters data of complete and non-completed cells under 1 sun illumination. cell J sc V oc FF η [ma/cm 2 ] [mv] [%] [%] EPH a (TiO 2 ) 15.6 ± ± ± ± 0.6 EP b 7.5 ± ± ± ± 0.2 PH a 11.5 ± ± ± ± 1.5 P c EPH a (ZnO) 19.1 ± ± ± ± 0.6 EPH d (CdS) 4.3 ± ± ± ± 0.1 a: 5 samples; b: 4 samples; c: 1 sample and d: 2 samples. SI3.- Nyquist Plot P sample: Figure SI3: Nyquist plot of P sample at DC bias of V= 0.1 V under 1 sun illumination. Symbols are experimental data and solid lines correspond to the fits using the equivalent circuit in Fig. 3c.

5 SI4.- Electron affinity, work function and band alignment: Figure SI4: Values for TiO 2, spiro-ometad and CH 3 NH 3 PbI 3 from Ref. 3, for Au, FTO and ZnO Ref. 4 and refereces herein; and for CdS from Ref. 5.

6 SI5.- Light absorption of CdS substrate and IPCE of CdS/perovskite sample. 1. Aprilia, A.; Wulandari, P.; Suendo, V.; Herman; Hidayat, R.; Fujii, A.; Ozaki, M. Influences of dopant concentration in sol gel derived AZO layer on the performance of P3HT:PCBM based inverted solar cell. Sol. Energy Mater. Sol. Cells 2013, 111 (0), Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker, R.; Gao, P.; Nazeeruddin, M. K.; Gratzel, M. Sequential deposition as a route to high-performance perovskitesensitized solar cells. Nature 2013, 499, Kim, H.-S.; Lee, C.-R.; Im, J.-H.; Lee, K.-B.; Moehl, T.; Marchioro, A.; Moon, S.-J.; Humphry-Baker, R.; Yum, J.-H.; Moser, J. E.; Gratzel, M.; Park, N.-G. Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%. Sci. Rep. 2012, 2, Mora-Sero, I.; Bertoluzzi, L.; Gonzalez-Pedro, V.; Gimenez, S.; Fabregat- Santiago, F.; Kemp, K. W.; Sargent, E. H.; Bisquert, J. Selective contacts drive charge extraction in quantum dot solids via asymmetry in carrier transfer kinetics. Nat Commun 2013, Fritsche, J.; Kraft, D.; Thißen, A.; Mayer, T.; Klein, A.; Jaegermann, W. Band energy diagram of CdTe thin film solar cells. Thin Solid Films 2002, (0),