Paper TF-WeM3
Single-step, Atmospheric CVD of Methylammonium Bismuth Iodide Perovskite Thin Films

Wednesday, November 1, 2017, 8:40 am, Room 20

Synthesis of methylammonium bismuth iodide (CH₃NH₃)₃Bi₂I₉) is achieved through a single step, atmospheric pressure, chemical vapor deposition (CVD) process. The precursors used are powders of bismuth iodide (BiI₃) and methylammonium iodide (CH₃NH₃I). These precursors are sublimated inside a tube furnace reactor with a well-controlled and predetermined temperature profile. The sublimated vapors are transported via Ar carrier gas to the cooler parts of the tube furnace, where simultaneous condensation and reaction between the two precursors leads to the formation of high quality (CH₃NH₃)₃Bi₂I₉ films on the wafer surface.

Structural and compositional information is obtained via grazing incidence X-ray diffraction (GI-XRD), SEM, TEM and XPS which confirm the (CH₃NH₃)₃Bi₂I₉ phase. Band-edge information is obtained via a combination of cyclic voltammetry and UV-vis spectroscopy. The band gap is revealed to be 1.9 eV. Temperature-dependent Hall measurements detect the recently observed ^[1] ferrielectric phase transition at ~150K via changes to the slope in the concentration vs. temperature and mobility vs. temperature curves. A room temperature electron concentration of 1.48 x 10¹⁹ cm^-3 and mobility of 7.13 cm²/V.sec is obtained for (CH₃NH₃)₃Bi₂I₉ films with good crystallinity.

Reference:

[1] Kamminga, M. E.; Stroppa, A.; Picozzi, S.; Chislov, M.; Zvereva, I. A.; Baas, J.; Meetsma, A.; Blake, G. R.; Palstra, T. T. M., Polar Nature of (CH₃NH₃)₃Bi₂I₉ Perovskite-Like Hybrids. Inorganic Chemistry 2017, 56, 33-41.