Structural, optical, and electrical properties of phasecontrolled cesium lead iodide nanowires

Transcription

1 Electronic Supplementary Material Structural, optical, and electrical properties of phasecontrolled cesium lead iodide nanowires Minliang Lai 1, Qiao Kong 1, Connor G. Bischak 1, Yi Yu 1,2, Letian Dou 1,2, Samuel W. Eaton 1, Naomi S. Ginsberg 1,2,3,4,5, and Peidong Yang 1,2,3,6 ( ) 1 Department of Chemistry, University of California, Berkeley, California 94720, USA 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3 Kavli Energy Nanosciences Institute, Berkeley, California 94720, USA 4 Molecular Biophysics and Integrative Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 5 Department of Physics, University of California, Berkeley, California 94720, USA 6 Department of Materials Science and Engineering, University of California, Berkeley, California 94720, USA Supporting information to DOI /s S1 Solution growth of yellow orthorhombic Y-CsPbI 3 nanowire mesh All of the chemicals were purchased from Sigma-Aldrich unless otherwise stated. 460mg PbI 2 (99.999%) was dissolved in 1 ml anhydrous dimethylformide (DMF), stirred at 70 C overnight before further use. The PbI 2 solution was spin on O 2 plasma treated glass substrates at 3,000 rpm for 60 s, then annealed at 100 C for 15 min. The PbI 2 film was carefully dipped into a glass vial with 2 ml 4 8 mg ml 1 CsI (99.999%)/methanol (anhydrous 99.8%), with the PbI 2 side facing up. The reaction was carried at room temperature for 12 h with the glass vial capped closely, then the substrate was taken out to wash in anhydrous isopropanol for 30 s. Then the sample was dried under 50 C for 5 min. The whole growth process was in a N 2 filled glovebox. S2 CsPbI 3 nanowire phase transition through annealing Synthesized Y-CsPbI 3 nanowire mesh film was heated slowly on a hot plate (Corning PC 240D) to 310 C (calibrated by IR thermometer) at an approximate rate of 10 C min 1, and the temperature remained at 310 C for 10 min. Then the film was quickly taken to metal base inside the glovebox (H 2 O < 0.1 ppm, O 2 < 0.1 ppm) for thermal quenching. The glovebox was purged for 10 min with N 2 to clear the possible gas residual from previous users before the annealing. During the quenching process, the temperature drops from 310 to 26 C within 2 s. For optical characterization, several CsPbI 3 nanowires were first dry transferred on clean Si substrate by slightly pressing Si substrate on CsPbI 3 nanowire mesh film before the annealing process. Address correspondence to p_yang@berkeley.edu

2 S3 Structural characterization SEM images were acquired by using a JEOL JSM-6340F field emission scanning electron microscope. The XRD pattern was acquired by using a Bruker AXS D8 Advance diffractometer equipped with a lynxeye detector, which used Cu Kα radiation. For B-CsPbI 3 XRD, the film was coated with PMMA first for protection before measured in air. Several droplets of 950 PMMA C4 solution (MicroChem) were dropped on the film and dried spontaneously in the glovebox before measured XRD in air. S4 TEM measurements Y-CsPbI 3 nanowires were transferred by lightly pressing a TEM grid on nanowire film. For B-CsPbI 3 nanowires, Y-CsPbI 3 nanowires were transferred on a TEM grid first, then went through the phase transition process in a glovebox as described above. The TEM images and corresponding SAED patterns were acquired by using an FEI Titan microscope operated at 200 kv. For SAED experiments, the electron dose-rate was controlled to be as low as ~10 ea 2 s 1 in order to minimize the electron beam damage. S5 PL measurements PL of nanowires were measured by using a 405 nm excitation from a laser diode with emission collected on a Nikon A1 microscope coupled to a multimode fiber coupled to a liquid-nitrogen-cooled Si CCD. Optical PL images were acquired via an Olympus IX71 inverted microscope coupled to a Zeiss AxioCam MRc5 camera. S6 Cathodoluminescence measurements Cathodoluminescence (CL) images were acquired with a modified Zeiss Gemini SUPRA 55 Scanning Electron Microscope (SEM). An aluminum parabolic reflector was positioned above the same sample in order to couple a 1.3 π sr of emission outside of the vacuum chamber through a quartz window. The emission images were collected using H and H photon counting modules (Hamamatsu) with an 85 nm bandpass filter centered at 510 nm and a 50 nm bandpass filter centered at 710 nm, respectively. All images were acquired at 3 kv with pixels and a scanning rate of 10 ms/line. Figure S1 SEM images of Y-CsPbI 3 nanowire growth at different concentration of CsI solution. (a) 2 mg ml 1, fat micro size wires. (b) 4 mg ml 1, nanowires with nm thickness. (c) 4 mg ml 1, nanowires within nm thickness. (d) 16 mg ml 1, dense film with few nanowires.

3 Figure S2 SAED patterns of different Y-CsPbI 3 nanowires ((a) and (b)) and the corresponding TEM images to same nanowires ((c) and (d)). Multiple SAED patterns confirm synthesized CsPbI 3 nanowires are in a non-perovskite orthorhombic phase (space group Pmna, a = Å, b = Å, c = Å). The growth direction can be indexed to [010]. Figure S3 (a) Image of as-synthesized Y-CsPbI 3 nanowire mesh film on glass. (b) B-CsPbI 3 film after phase transition coated by PMMA. The edges of film were scratched for better protection from air. (c) SEM image of post transformed B-CsPbI 3 film. The nanowire morphology was not well preserved, probably due to too high density of nanowires. Dry transfer onto Si substrate (d) helps preservation of nanowire morphology and enables better study down to single nanowire level. Nano Research

4 Nano Res. Figure S4 SAED patterns of different B-CsPbI3 nanowires ((a) and (b)) and the corresponding TEM images to same nanowires ((c) and (d)). Multiple SAED patterns can be assigned to a simulated perovskite orthorhombic phase (space group Pmnb, a = 8.89 Å, b = 8.95 Å, c = Å). Figure S5 (a) XRD patterns of B-CsPbI3 (red), simulated cubic phase (black), and standard non-perovskite yellow phase (blue). (b) Experimental XRD patterns B-CsPbI3 (red) and simulated XRD patterns of perovskite orthorhombic CsPbI3 from Fig. S4 (black). Figure S6 CL spectra of Y-CsPbI3 nanowires (a) and B-CsPbI3 nanowires (b).

5 Figure S7 Bright field optical image of a B-CsPbI 3 nanowire (a) and a Y-CsPbI 3 nanowire (c) on Au gold electrode, with corresponding PL images to confirm black phase (b) and yellow phase (d). The scale bar is 10 µm. Figure S8 Meta-stable state of post transformed B-CsPbI 3 nanowires. (a) XRD patterns of B-CsPbI 3 transited back to yellow phase after heated to 200 C. PL images of B-CsPbI 3 nanowires (b) and after 200 C heating (c). (d) PL spectrum of B-CsPbI 3 nanowires after heating further confirmed the yellow phase. (e) A hypothetical illustration of black phase as a meta-stable state and yellow phase as a global stable state. Meta-stable B-CsPbI 3 gained certain thermal energy to overcome the barrier, then transited to the global stable Y-CsPbI Nano Research