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In this work, we systematically explored the photochemical stability of MAPbI3 interfaces with five different charge transport layers (CTLs): substituted naphthalene (NDI) and perylene (PDI) diimides, fullerene derivatives PC61BM and PC71BM, and widely used hole transport material spiro-OMeTAD. While studying these model systems, we revealed several important interfacial degradation pathways. First, we demonstrated that diimides (both NDI and PDI) strongly accelerate the photodegradation of MAPbI3 since they specifically interact with PbI2 formed as one of the perovskite degradation products. Fullerene derivatives, in turn, absorb another decomposition product, methylammonium iodide (MAI), which also results in accelerated ageing of the perovskite films deposited atop fullerene-based CTLs. However, both fullerene derivatives and spiro-OMeTAD have excellent encapsulation properties and strongly suppress photodecomposition of MAPbI3, when the perovskite films are placed underneath. Unfortunately, the observed impressive perovskite bulk phase stabilization using PC61BM, PC71BM and spiro-OMeTAD coatings does not improve the operation lifetime of photovoltaic cells due to interfacial degradation processes. TOF-SIMS analysis has revealed accumulation of the perovskite decomposition products (presumably CH3I) in the spiro-OMeTAD layer as well as a noticeable degradation at the interface with the electron transport tin dioxide layer. The obtained results emphasize the major challenge in the development of perovskite solar cells with long operation lifetime related to poor stability of the functional perovskite/CTL interfaces.

Electrochemical strain microscopy (ESM) is a scanning probe microscopy (SPM) method in which the local electrodiffusion is probed via application of AC voltage to the SPM tip and registration of resulting electrochemical strain. Here, we implemented ESM to measure local strain in bulk LiMn2O4 cathodes of a commercial Li-battery in different states of charge to investigate distribution of Li-ion mobility and concentration. Ramped AC ESM imaging and voltage spectroscopy were used to find the most reliable regime of measurements allowing separating and diminishing different contributions to ESM. This is not a trivial task due to complex geometry of the sample and various obstacles resulting in less predictable contributions of different origins into ESM response: electrostatic tip-surface interactions, charge injection, electrostriction, and flexoelectricity. Understanding and control of these contributions is an important step towards quantitative interpretation of ESM data. (C) 2016 AIP Publishing LLC.

Based on experimental data on sputtering of copper-graphite cathodes, we propose a mechanism of equirate sputtering of elements of mosaic targets prepared from materials the sputtering yields of which differ by almost an order of magnitude. The mechanism takes into account the occurrence of a height discontinuity between the mosaic elements at the initial stage of sputtering, the redistribution of ion fluxes between the elements, and the effects related to the mass transfer in plasma and the implantation of sputtered atoms into the mosaic elements of the different variety.