Fig 1.
Presence of Pb° and chemical contaminants.
XPS data showing the Pb 4f, C 1s and O 1s core level peaks for the as-is and cleaved surfaces of crystals. Pb 4f peaks show a shoulder (red) ca. 2 eV below the main peaks (green), corresponding to Pb°. C 1s core peaks can be split into three components: amorphous carbon (grey), carbon belonging to methylammonium (orange), carbon belonging to oxygen-functionalities (red). Oxygen functionalities, depicted by O 1s comprise of O-H (blue) and adsorbed water (green) components. Possibly, the O-C species overlaps the O-H component.
Table 1.
Summary of atomic ratio determined from XPS relative atomic quantification.
Fig 2.
(A) Schematic showing the treatment process (B) XPS data showing the Pb 4f core peak from the top surface of the brominated crystals. Suppression of the Pb° peaks is found (C) XRD of the various MAPbBr3 crystals showing the (002) scattering peak shift (D) PL peaks for the various conditions. A blue-shift of ca. 2 nm is observed after Br-vapor treatment.
Fig 3.
(A) Conductivity, (B) Carrier density, and (C) Mobility, of the untreated and Br-treated crystals obtained from Hall measurements. The measurements reveal enormous gains in charge transport. ‘Br-20 min’ and ‘Br-60 min’ represent 20-min and 60-min bromine-treated samples, respectively. Values are averages over 4–5 crystals (see S3 Table for details).