Coexistence of Two Electronic Nano-Phases on a CH3NH3PbI3-xClx Surface Observed in STM Measurements

• Published in: ACS applied materials & interfaces Vol. 8; no. 42; pp. 29110 - 29116
• Main Authors: Yost, Andrew J, Pimachev, Artem, Ho, Chun-Chih, Darling, Seth B, Wang, Leeyih, Su, Wei-Fang, Dahnovsky, Yuri, Chien, TeYu
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society (ACS) 26.10.2016
• Subjects: cross-sectional scanning tunneling microscopy; density functional theory; electronic phase; MATERIALS SCIENCE; mixed halide; nano-phase; organometallic halide perovskite
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.6b07721

Scanning tunneling microscopy is utilized to investigate the local density of states of a CH3NH3PbI3-xClx perovskite in cross-sectional geometry. Two electronic phases, 10-20 nm in size, with different electronic properties inside the CH3NH3PbI3-xClx perovskite layer are observed by the dI/dV mapping and point spectra. A power law dependence of the dI/dV point spectra is revealed. In addition, the distinct electronic phases are found to have preferential orientations close to the normal direction of the film surface. Density functional theory calculations indicate that the observed electronic phases are associated with local deviation of I/Cl ratio, rather than different orientations of the electric dipole moments in the ferroelectric phases. By comparing the calculated results with experimental data we conclude that phase A (lower contrast in dI/dV mapping at -2.0 V bias) contains a lower I/Cl ratio than that in phase B (higher contrast in dI/dV).