Determination of the True Lateral Grain Size in Organic-Inorganic Halide Perovskite Thin Films.

In this letter, methylammonium lead iodide (MAPbI) thin films were examined via piezoresponse force microscopy (PFM) and nanoindentation (NI) to determine if long-range atomic order existed across the full width and depth of the apparent grains. From the PFM, the piezoelectric response of the films was strongly correlated with low-index planes of the crystal structure and ferroelastic domains in macroscale solution-grown MAPbI crystals, which implied long-range order near the top surface. From the NI, it was found that the induced cracks were straight and extended across the full width of the apparent grains, which indicated that the long-range order was not limited to the near-surface region, but extended through the film thickness.

Electronic and Morphological Inhomogeneities in Pristine and Deteriorated Perovskite Photovoltaic Films.

We perform scanning microwave microscopy (SMM) to study the spatially varying electronic properties and related morphology of pristine and degraded methylammonium lead-halide (MAPI) perovskite films fabricated under different ambient humidity. We find that higher processing humidity leads to the emergence of increased conductivity at the grain boundaries but also correlates with the appearance of resistive grains that contain PbI. Deteriorated films show larger and increasingly insulating grain boundaries as well as spatially localized regions of reduced conductivity within grains.

Electrical property heterogeneity at transparent conductive oxide/organic semiconductor interfaces: mapping contact ohmicity using conducting-tip atomic force microscopy.

We demonstrate mapping of electrical properties of heterojunctions of a molecular semiconductor (copper phthalocyanine, CuPc) and a transparent conducting oxide (indium-tin oxide, ITO), on 20-500 nm length scales, using a conductive-probe atomic force microscopy technique, scanning current spectroscopy (SCS). SCS maps are generated for CuPc/ITO heterojunctions as a function of ITO activation procedures and modification with variable chain length alkyl-phosphonic acids (PAs). We correlate differences in small length scale electrical properties with the performance of organic photovoltaic cells (OPVs) based on CuPc/C(60) heterojunctions, built on these same ITO substrates.

Surface-initiated synthesis of poly(3-methylthiophene) from indium tin oxide and its electrochemical properties.

Poly(3-methylthiophene) (P3MT) was synthesized directly from indium tin oxide (ITO) electrodes modified with a phosphonic acid initiator, using Kumada catalyst transfer polymerization (KCTP). This work represents the first time that polymer thickness has been controlled in a surface initiated KCTP reaction, highlighting the utility of KCTP in achieving controlled polymerizations. Polymer film thicknesses were regulated by the variation of the solution monomer concentration and ranged from 30 to 265 nm.