No abstract

The open circuit voltage in ultrathin amorphous silicon solar cells is found to increase with light energy ͑frequency͒, due to extraction of hot electrons. The ultrathin nature of these junctions also leads to large internal electric fields, yielding reduced recombination and increased current. A simple phenomenological argument provides a qualitative understanding of these effects and gives guidelines for designing future, high-efficiency, hot electron solar cells. A J sc [I-V] J sc [EQE] P/P(60 nm) J sc (mA/cm 2 ) D (nm) J sc Z h u , e t a l . A/A(60 nm) FIG. 3. ͑Color online͒ Variation of short circuit current density with total junction thickness. J sc vs D under AM1.5 illumination, as measured from I-Vs ͑squares͒, calculated by integrating EQE͑͒ ͑triangles͒, integrated optical absorbance A, normalized to the D = 60 nm value ͑circles͒, and normalized power density as modeled in Ref. 17 ͑dash͒.233121-2 Kempa et al. Appl. Phys. Lett. 95, 233121 ͑2009͒

We report on the design, fabrication, and performance of a nanoporous, coaxial array capacitive detector for highly sensitive chemical detection. Composed of an array of vertically aligned nanoscale coaxial electrodes constructed with porous dielectric coax annuli around carbon nanotube cores, this sensor is shown to achieve parts per billion level detection sensitivity, at room temperature, to a broad class of organic molecules. The nanoscale, 3D architecture and microscale array pitch of the sensor enable rapid access of target molecules and chip-based multiplexing capabilities, respectively.

Non-planar solar-cell devices have been promoted as a means to enhance current collection in absorber materials with charge-transport limitations. This work presents an analytical framework for assessing the ultimate performance of non-planar solar-cells based on materials and geometry. Herein, the physics of the p-n junction is analyzed for low-injection conditions, when the junction can be considered spatially separable into quasi-neutral and space-charge regions. For the conventional planar solar cell architecture, previously established one-dimensional expressions governing charge carrier transport are recovered from the framework established herein. Space-charge region recombination statistics are compared for planar and non-planar geometries, showing variations in recombination current produced from the space-charge region. In addition, planar and non-planar solar cell performance are simulated, based on a semi-empirical expression for short-circuit current, detailing variations in charge carrier transport and efficiency as a function of geometry, thereby yielding insights into design criteria for solar cell architectures. For the conditions considered here, the expressions for generation rate and total current are shown to universally govern any solar cell geometry, while recombination within the spacecharge region is shown to be directly dependent on the geometrical orientation of the p-n junction.

The size and orientation of Sn grains in Pb-free, near eutectic SAC solder joints were examined. A clear dependence of the thermomechanical response of these solder joints on Sn grain orientation was observed. Solder balls with Sn grains of particular orientation (a-axis perpendicular to the substrate) were observed to fail before neighboring balls with different orientations. This results from the fact that the coefficient of thermal expansion of Sn along the a-axis is half the value along the c-axis; joints observed to be damaged had maximum mismatch in the coefficient of thermal expansion between solder and substrate at the joint interface, as well as tensile stress modes during the hot part of the cycle.