Water Infiltration in Methylammonium Lead Iodide Perovskite: Fast and Inconspicuous

While the susceptibility of CH3NH3PbI3 to water is well documented, water influence on device performance is not well understood. Herein we use infrared spectroscopy to show that water infiltration into CH3NH3PbI3 occurs much faster and at much lower humidity than previously thought. We propose a molecular model where water molecules have a strong effect on the hydrogen bonding between the methylammonium cations and the Pb-I cage. Furthermore, the exposure of CH3NH3PbI3 to ambient environment increases the photocurrent of films in lateral devices by more than one order of magnitude. The observed slow component in the photocurrent buildup indicates that the effect is associated with enhanced proton conduction when light is combined with water and oxygen exposure.C.M. and M.S. acknowledge support by the Heidelberg Graduate School of Fundamental Physics. A.A.B. is a Royal Society University Research Fellow.This is the author accepted manuscript. The final version is available from the American Chemical Society via http://dx.doi.org/10.1021/acs.chemmater.5b0388

Impact of Bi3+ heterovalent doping in organic-inorganic metal halide perovskite crystals

Intrinsic organic-inorganic metal halide perovskites (OIHP) based semiconductors have shown wide applications in optoelectronic devices. There have been several attempts to incorporate heterovalent metal (e.g., Bi3+) ions in the perovskites in an attempt to induce electronic doping and increase the charge carrier density in the semiconductor. It has been reported that inclusion of Bi3+ decreases the band gap of the material considerably. However, contrary to the earlier conclusions, despite a clear change in the appearance of the crystal as observed by eye, here we show that the band gap of MAPbBr3 crystals does not change due the presence of Bi3+ in the growth solution. An increased density of states in the band gap and use of very thick samples for transmission measurements, erroneously give the impression of a band gap shift. These sub band gap states also act as nonradiative recombination centers in the crystals

Investigation of Solution-Processed Ultrathin Electron Injection Layers for Organic Light-Emitting Diodes

We study two types of water/alcohol-soluble aliphatic amines, polyethylenimine (PEI) and polyethyleni-mine-ethoxylated (PEIE), for their suitability as electron injection layers in solution-processed blue fluorescent organic light-emitting diodes (OLEDs). X-ray photoelectron spectroscopy is used to determine the nominal thickness of the polymer layers while ultraviolet photoelectron spectroscopy is carried out to determine the induced work-function change of the silver cathode. The determined work-function shifts are as high as 1.5 eV for PEI and 1.3 eV for PEIE. Furthermore, atomic force microscopy images reveal that homogeneous PEI and PEIE layers are present at nominal thicknesses of about 11 nm. Finally, we solution prepare blue emitting polymer-based OLEDs using PEI/PEIE in combination with Ag as cathode layers. Luminous efficiency reaches 3 and 2.2 cd A−1, whereas maximum luminance values are as high as 8000 and 3000 cd m−2for PEI and PEIE injection layers, respectively. The prepared devices show a comparable performance to Ca/Ag OLEDs and an improved shelf lifetime