Metal/Ion Interactions Induced p-i-n Junction in Methylammonium

Transcription

1 Supporting Information for Metal/Ion Interactions Induced p-i-n Junction in Methylammonium Lead Triiodide Perovskite Single Crystals Ting Wu, Rupam Mukherjee, Olga S. Ovchinnikova,, Liam Collins,, Mahshid Ahmadi, Wei Lu, Nam-Goo Kang, Jimmy W. Mays, Stephen Jesse,, David Mandrus, Bin Hu, * Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, 37996, USA Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Institute for Functional Imaging of Materials, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Department of Chemistry, University of Tennessee, Knoxville, Tennessee, 37996, USA * bhu@utk.edu S1

2 I. Experimental Procedure Single crystal growth and sample preparation: The MAPbI 3 single crystals were prepared by solutionbased growth method with a designed cooling program. The precursor solution for crystal growth was prepared according to reference 1. Afterward, the precursor solution was separated into several 20 ml vials. The vial caps were carefully sealed with Teflon tapes, while the vials were kept in an oil bath on top of a digital hot plate with the temperature programmed as 100 /2 hr, 90 /2 hr, 80 /2 hr, 70 /2 hr, 60 /2 hr, 55 /99 hr, 50 /99 hr, and 45 /99 hr. Finally, the crystals were carefully taken out from the solution and dried with Kim wipes to gain mirror-like surfaces, and then rinsed with diethyl ether for at least three times and vacuum dried at room temperature. The single crystals with the thickness of ~1.5 mm were selected for the present work. The (100) facets of the single crystals were then carefully polished by grinding paper (3M 2500) on Struer Roto. The samples were prepared with metal contacts on the polished (100) facets. The metal contacts, such as Au (70 nm) and Ag (100 nm), were thermally evaporated under the vacuum of Torr to prepare Au/SC/Ag and Ag/SC/Ag samples. Single crystal characterizations: The trap density of as-grown single crystals were characterized by measuring the current-voltage characteristics in dark condition using Keithley 2400 in the nitrogen filled glove box; The hole-injection only devices (Au/SC/Au) and electron-injection only devices (Ag/C 60 :PCBM/SC/C 60 :PCBM/Ag) were measured to characterize the hole- and electron- trap density, respectively. Temperature dependent Hall Effect was measured using PPMS (Quantum Design, Inc.) to study the type of majority carriers and the carrier density in dark condition. Seebeck effect measurements: The Seebeck effect measurements were performed in dark condition and nitrogen environment with variable temperatures from 296 K to 355 K. The single crystal samples (Au/SC/Ag or Ag 1 /SC/Ag 2 ) were sandwiched between two ITO glass substrates with silver paste. Two S2

3 ceramic heaters (HT24S, ThorLabs) were attached to the two ITO substrates, generating a controllable temperature difference ranging from -4 K to 4 K between the two contact surfaces using the DC power supply. K-type thermocouple wires were used to measure the temperatures of the two contact surfaces by the Analog/Digital input/output system (model 100, from InstruNet) combined with DASYLab 11.0 interface. Simultaneously, two copper wires were glued on the ITO substrates to measure the potential difference between the LT and HT terminals using Keithley Time-of-flight secondary ion mass spectrometry (TOF-SIMS) analysis: The TOF-SIMS data was acquired by TOF-SIMS.5 (Ion-Tof, Munster, Germany) using a 30 kev Bi ion gun as the primary gun with a focused ion beam spot size of ~ 5 µm, and a m/δm resolution of ~11,000. The images were collected with a spatial resolution of points across a 500 µm imaging area. Depth profiling of the sample was carried out using a Cs sputtering source operated at 1 kev and 65 na; sputtering for 3 s per slice over a 600 µm total area. The depth profiling data was reconstructed from 450 s of total sputtering time. All experiments were performed in positive ion mode with iodine forming [Cs 2 I] + clusters. S3

4 Current (A) Current (A) II. Characterization on Trap Density of Grown Single Crystals a 10-6 Hole only device b 10-6 Electron only device VTFL 5 V ntrap~3x10 9 cm VTFL 9 V ntrap~1.14x10 10 cm Voltage (V) Voltage (V) Figure S1. Characterization of trap density of grown single crystals based on Space Charge Limit Current (SCLC) model. (a) Dark current-voltage (I-V) characteristics of the hole-only device with the structure of Au/SC/Au. (b) Dark I-V characteristics of electron-only device with the structure of Ag/C60:PC 61 BM/SC/C60:PC 61 BM/Ag, where C 60 :PCBM interlayer was drop cast on the single crystal from the mixed solution of Dichloroform (C 60 :PCBM=10mg:10mg, 20 mg/ml). The dark I-V curves present three regimes: (i) ohmic regime (red), (ii) trap filled limit (TFL) regime (blue) and (iii) trap-free Child`s regime (green). The onset voltage of TFL regime is defined as V TFL, which can be used to determine the trap states density (n trap ) based on equation: n trap = 2εε 0V TFL, where ε qd 2 0 is the vacuum permittivity, and ε r is the relative dielectric constant of MAPbI 3 (ε r =32), 1 q is the elementary charge, and d is the thickness of crystal. The calculated the hole- (electron-) trap densities (n trap ) are ~ cm 3 (~ cm 3 ). S4

5 Weight (%) III. Thermal stability of MAPbI 3 Single Crystals a In air Temperature (K) Figure S2. Thermal stability of MAPbI 3 single crystal in the air. (a) Thermogravimetric analysis (TGA) of the thermal stability of a MAPbI 3 single crystal with air condition from room temperature to 1100 K. The shadow area indicates the temperature window for Seebeck effect and Hall effect measurements. The weight loss in air at 360 K is less than 0.1%, suggesting promising thermal stability of MAPbI 3 single crystal. (b~e) Images of a single crystal heated at 363 K on a hot plate in ambient condition with controlled humidity of 35~40 % for 0 hr, 2 hr, 4 hrs and 24 hrs. The crystal surface maintained in black color in 24 hrs without visible yellowish color, indicating that the decomposition was not occurred to form the PbI 2 phase at the surface of MAPbI 3 single crystal. These studies suggest excellent thermal stability of MAPbI 3 single crystal in ambient condition S5

6 IV. Surface Treatment of Grown Single Crystals Figure S3. Optical microscopic images of crystal surface with and without treatment. (a) As-grown crystal, (b) polished crystal and (c) chemically etched crystal with isopropanol (IPA, anhydrous). The rough surface of the as-grown crystal is due to the residual chemicals from the precursor solution. The striped pattern of polished crystal surface is caused by mechanical grind with sandpapers. IPA is expected to dissolve the organic compounds, including the residual MAI from the solution and as well as the organic components from perovskite crystal surface. S6

7 V. TOF-SIMS Analysis of Au/MAPbI 3 Interface Figure S4. TOF-SIMS analysis of the local structure at Au/MAPbI 3 interface. The sample of a crystal partially covered by Au thin film was excited by 1 kev Cs + ion beam, which focuses on the area right across the boundary between Au and crystal surfaces. The left triangle is covered by Au layer. It should be noted that the notation of the emitted ions or ion clusters just reflect the possible chemical composition rather than exact chemical formula. During the ionization process, different type of ions, such as (a) [CsAu] +, (b) [Cs 2 I] +, (c) CH 3 NH + 3 and (d) Pb +, were immediately emitted from the surface without Au layer, and eventually emitted from the surface with Au layer once Au was completely sputtered away. In addition, some gold complexes, such as (e) [Au(NH 2 CH 3 )] +, (f) [AuN] +, (g) [Au(C 2 NH 7 )] +, and (h) [AuPb] + were observed from the surface covered by Au when the underneath perovskite was exposed to ion beam. S7

8 VI. TOF-SIMS Analysis of Ag/MAPbI 3 Interface Figure S5. TOF-SIMS analysis of the local structure at Ag/MAPbI 3 interface. The crystal partially covered by Ag was sputtered by Cs + beam. During the entire ionization process, no ionic clusters, consisting of organic molecules and Ag, were detected. S8

9 Current ( A) VII. Electrical characterization of the Au/SC/Ag samples White light 785 nm 10-3 Dark Voltage (V) Figure S6. Current-voltage characteristics under the illumination by white light and close to band edge excitation (785 nm). The dark J-E curves of Au/SC/Ag sample behaves as a diode with rectifying property. The sample generates photoresponses not only under white light illumination with Voc=0.57 V but also under the excitation close to the band edge (785 nm) with Voc=0.66 V. Photoexcitation was applied from the edge of the crystal. This indicates the potential application for near-infrared light detection. References 1 Dong, Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Science 2015, 347, 967. S9