Chalcopyrite-based materials for photovoltaic devices tend to exhibit complex structural imperfections originating from their polycrystalline nature; nevertheless, properly controlled devices are surprisingly irrelevant to them in terms of resulting device performances. The present work uses atom probe tomography to characterize co-evaporated high-quality Cu(In,Ga)Se2 (CIGS) films on flexible polyimide substrates either with or without doping with Na or doping with Na followed by K via a post-deposition treatment. The intent is to elucidate the unique characteristics of the grain boundaries (GBs) in CIGS, in particular the correlations/anti-correlations between matrix elements and the alkali dopants. Various compositional fluctuations are identified at GBs irrespective of the presence of alkali elements. However, [Cu-poor and Se/In,Ga-rich] GBs are significantly more common than [Cu-rich and Se/In,Ga-poor] ones. In addition, the anti-correlations between Cu and the other matrix elements are found to show not only regular trends among themselves but also the association with the degree of alkali segregation at GBs. The Na and K concentrations exhibited a correlation at the GBs but not in the intragrain regions. Density functional theory calculations are used to explain the compositional fluctuations and alkali segregation at the GBs. Our experimental and theoretical findings not only reveal the benign or beneficial characteristics of the GBs of CIGS but also provide a fundamental understanding of the GB chemistry in CIGS-based materials.

Microwire (MW)-based radial junction crystalline silicon (c-Si) solar cells have great potential as an emerging energy device with an efficiency of over 20%. However, the competitive efficiency of MW-based c-Si solar cells in realizing a wafer-scale device is limiting its commercialization. In this study, the aim is to demonstrate that conventional fabrication techniques can be applied to MWbased solar cells while not only increasing the size from the lab-scale to the wafer-scale but also retaining an efficiency of >20%. Surprisingly, an improvement in open-circuit voltage and fill factor is observed with an increase in device size, due to the reduction of recombination loss at the device edge. Finally, a successful demonstration of 21.1% efficiency at 4-inch wafer-scale (25 cm 2 ) in c-Si MW solar cell is observed, while an efficiency of 20.6% at a lab-scale size (1 cm 2 ) is observed.

Live video recording of intracellular material transport is a promising means of deciphering the fascinating underlying mechanisms driving life at the molecular level. Such technology holds the key to realizing real-time observation at appropriate resolutions in three-dimensional (3D) space within living cells. Here, we report an optical microscopic method for probing endosomal dynamics with proper spatiotemporal resolution within 3D space in live cells: plasmonic dark-field STORM (pdf-STORM). We first confirmed that pdf-STORM has a spatial resolution comparable to that of scanning electron microscopy. Additionally, by observing two optical probes within a single organelle, we were able to track rotational movements and demonstrate the feasibility of using pdf-STORM to observe the angular displacements of an endosome during a “tug-of-war” over an extended period. Finally, we show various biophysical parameters of the hitherto unelucidated dynamics of endosomes—angular displacement is discontinuous and y -axis movement predominates and follows a long-tail distribution.