COMMUNICATION (1 of 7)and CsSnI 3 has, to date, been less encouraging, with solar cell efficiencies of <5% for solution-processed thin film devices [10] that are likely limited by the low degree of crystalline ordering. [11] Indeed, structural ordering has been linked in traditional semiconductors to (a) carrier transport, where mobilities increase from amorphous-Si (1 cm 2 V −1 s −1 ) [12] to single crystalline Si (1400 cm 2 V −1 s −1 ), [13] (b) recombination rates, where unpassivated grain boundaries act as quenching sites for charge carriers and excited states, and (c) quantum confinement, which can make even Si an excellent NIR emitter with luminescent efficiency >60%. [14] These factors, among others, have motivated the recent interest in halide perovskite single crystal growth. [15] Thus, one of the main challenges for enhancing the properties of halide perovskites for high end optoelectronic applications is to obtain epitaxial crystalline films that can also be integrated into heteroepitaxial and quantum well structures. The epitaxial growth is a key step

The synthesis and characterization of a lead iodide layered perovskite, [NH2C­(I)NH2]2(CH3NH3)2Pb2I8, is described. The combination of an ideal bandgap of 1.61 eV and excellent compositional stability under ambient conditions make it a promising candidate for integration in solar cells. Planar solar cells utilizing [NH2C­(I)NH2]2(CH3NH3)2Pb2I8 exhibit two interesting phenomena in the photovoltaic performance: an exponential dependence of J sc on incident light intensity and abnormal J–V response. To investigate the photophysical properties of [NH2C­(I)NH2]2(CH3NH3)2Pb2I8 perovskite planar solar cells, intensity-modulated photocurrent spectroscopy (IMPS) and electrochemical impedance spectroscopy (EIS) were conducted. It is found that the planar structured solar cells of the layered perovskite suffer from bulk recombination which limits the charge collection and photocurrent. Use of a mesoporous TiO2 scaffold layer largely overcomes the recombination limitations of the layered perovskite and significantly improves the photovoltaic performance.

Using photoconductive atomic force microscopy and Kelvin probe force microscopy, we characterize the local electrical properties of grains and grain boundaries of organic-inorganic hybrid perovskite (CH3NH3PbI3) thin films on top of a poly(3,4-ethylenedioxythiophene)-polystyrene sulfonate (PEDOT:PSS)/ITO substrate. Three discrete photoconductivity levels are identified among perovskite grains, likely corresponding to the crystal orientation of each grain. Local J-V curves recorded on these grains further suggest an anti-correlation behavior between the short circuit current (JSC) and open circuit voltage (VOC). This phenomenon can be attributed to diffusion-limited surface recombination at the non-selective perovskite-tip contact, where a higher carrier mobility established in the perovskite grain results in an enhanced surface recombination and thus a lower VOC. In addition, the photoresponse of perovskite films displays a pronounced heterogeneity across the grain boundaries, with the boundaries formed between grains of the same photoconductivity level displaying even enhanced photocurrent and open circuit voltage compared to those of the adjacent grain interiors. These observations highlight the significance of controlling the microstructure of perovskite thin films, which will be a necessary route for further improving the efficiency of perovskite solar cells.

Organic–inorganic halide perovskites have emerged as one of the most promising materials for photovoltaic applications. Because of the polycrystalline nature of perovskite thin films, it is crucial to investigate the impact of microstructures on device performance. In this study, we employ ramp-annealing to tailor the texture of perovskite thin films via controlling the nucleation of perovskite grains. Electrochemical impedance spectroscopy studies further suggest that the thin film texture impacts not only the charge collection at the contact but also the carrier transport in the bulk perovskite layer. The combination of the two effects leads to enhanced performance in devices constructed of preferentially oriented perovskite thin films.

We demonstrate in-plane field-free-switching spin-orbit torque (SOT) magnetic tunnel junction (MTJ) devices that are capable of low switching current density, fast speed, high reliability, and, most importantly, manufactured uniformly by the 200-mm-wafer platform. The performance of the devices is systematically studied, including their magnetic properties, switching behaviors, endurance and data retention. The successful integration of SOT devices within the 200-mm-wafer manufacturing platform provides a feasible way to industrialize SOT MRAMs. It is expected to obtain excellent performance of the devices by further optimizing the MTJ film stacks and the corresponding fabrication processes in the future.