Electrical and Optical Tunability in All-Inorganic Halide. Perovskite Alloy Nanowires

Transcription

1 Supporting Information for: Electrical and Optical Tunability in All-Inorganic Halide Perovskite Alloy Nanowires Teng Lei, 1 Minliang Lai, 1 Qiao Kong, 1 Dylan Lu, 1 Woochul Lee, 2 Letian Dou, 3 Vincent Wu, 4 Yi Yu, 5 Peidong Yang, 1, 6, 7, 8 * 1 Department of Chemistry, University of California, Berkeley, CA 94720, USA 2 Department of Mechanical Engineering, University of Hawaii at Manoa, Honolulu, Hawaii, 96822, USA 3 Davidson School of Chemical Engineering, Purdue University, West Lafayette, Indiana, 47907, USA 4 Department of Chemical & Biomolecular Engineering, University of California, Berkeley, CA 94720, USA 5 School of Physical Science and Technology, Shanghai Tech University, Shanghai, , China 6 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA 7 Department of Materials Science and Engineering, University of California, Berkeley, CA 94720, USA 8 Kavli Energy NanoScience Institute, Berkeley, CA 94720, USA * To whom correspondence should be addressed: p_yang@berkeley.edu (P.Y.)

2 S1 Synthesis method: CsPb x Sn 1-x I 3 nanowires were synthesized on clean substrates that were loaded with a layer of PbI 2 and allowed to react in a solution of CsI and SnI 2 in anhydrous 2-propanol. All reagents were used as received without further purification. To grow CsPb x Sn 1-x I 3 nanowires, glass substrates are cleaned by sequential sonication in 2-propanol, acetone and deionized water, which is followed by drying in a 100 C oven. Subsequent steps are performed in an argon-filled glove box with an oxygen level of < 1.0 ppm and a H 2 O level of < 1.0 ppm. This condition is essential for the synthesis because SnI 2 can be quite easily oxidized in a higher concentration of O 2 atmosphere. 460mg PbI 2 (99.999%, anhydrous beads, Aldrich) was dissolved in 1 ml anhydrous dimethylformide (DMF), stirred at 90 C overnight before further use. The PbI 2 solution was spun on the O 2 plasma treated glass substrates at 3,000 rpm for 40 s, then annealed at 100 C for 10 min. The PbI 2 film was carefully dipped into a glass vial with 1.5 ml 4 mg ml -1 CsI (99.999%, anhydrous beads, Aldrich), and 0.25, 0.5, 1, 1.5, 2, 2.5, 3 mg ml -1 SnI 2 (99.999%, ultra-dry, Alfa Aesar) / methanol (anhydrous 99.8%, Aldrich), with the PbI 2 side facing up. The reaction was carried at room temperature for 12 h with the glass vial capped tightly; the substrate was then taken out to be quickly washed in anhydrous 2-propanol and any excess solution was wiped away with a kimwipe. After synthesis, the sample was stored and transported in a sealed centrifuge tube to minimize air/humidity exposure. The NW mesh was used for XRD, phase transition and optical studies, and the single NW was used for TEM and electrical measurement. S2 Structural and composition characterization: SEM images were acquired by using a JEOL JSM-6340F field emission scanning electron microscope. For TEM measurement, CsPb x Sn 1-x I 3 NWs were transferred on a TEM grid by gently press the TEM grid on the NWs mesh. The TEM images, EDS mapping, line scan and SAED patterns were acquired by using the FEI Titan microscope in National Center for Electron Microscope. All the measurements were

3 operated at 300 kv. Due to the sensitivity of perovskite materials to electron beam, lower doses of electron beam was used. The XRD pattern was acquired by using a Bruker AXS D8 Advance diffractometer equipped with a lynxeye detector, which used Cu Kα radiation. To get the XRD of the black phase CsPb x Sn 1-x I 3 NWs, the film was coated with UV curing epoxy (Epoxy Technology) and exposed to a UV curing LED for half an hour to be protected from air. S3 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. Figure S1. More SEM images from different magnification.

4 Figure S2. Quantification results for the line scan along (a) and across (b) the NW. Figure S3. EDS quantification for different area on a single NW. Figure S4. DSC for the confirmation of phase transition temperature.

5 Figure S5. SAED patterns of different Y phase CsPbxSn1-xI3 nanowires (a), (b) and the corresponding TEM images to same nanowires. Multiple SAED patterns confirm the as-synthesized CsPbxSn1-xI3 NWs are in a non-perovskite orthorhombic phase (space group Pnam). Pattern (c) and (d) show SAED of different converted CsPbxSn1-xI3 NWs which are orthorhombic perovskite phase. Figure S6. HRTEM images of representative NWs, showing the single-crystalline structure.

6 Figure S7. Optical properties of Y CsPb x Sn 1-x I 3 nanowires. Calculated band gap (a) from their absorption spectrum. (b) PL of Y CsPb x Sn 1-x I 3 nanowires under the same laser excitation power. The Y CsSnI 3 intensity is multiplied by 5 times and the X=0.94 is multiplied by a factor of 1/3. Figure S8. Tauc plots of B-γ phase CsPb x Sn 1-x I 3 NWs with different compositions.

7 Figure S9. Absorption spectrum of B-γ phase CsPb x Sn 1-x I 3 NWs with different compositions and their calculated band gaps from Tauc plots. Figure S10. (a) SEM images of suspended micro-island devices. Single B-γ CsPb x Sn 1-x I 3 (X=0.13) nanowire is suspended between two membranes. The Seebeck measurement direction is along the growth direction of the NW. (b) Experimental data of Seebeck coefficient for individual B-γ CsPb x Sn 1-x I 3 nanowires at 300K.