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We investigate on narrow bandgap CIGSe solar cells for tandem application in a spectral splitting devices. Numerical simulations using SCAPS are performed to optimize the Ga content throughout the absorber layer, depending on the illumination condition (AM 1.5 and tandem conditions using two different splitting filters; 620 nm and 880 nm). The simulations show a strong dependence of the efficiency on the minimum bandgap of the absorber, but not on the depth of the narrow bandgap region. Narrow bandgap CIGSe solar cells are experimentally realized and electrically characterized. A similar trend as what was deduced from the simulation is observed on the experiments when the solar cells are characterized in the tandem conditions. For the 880 nm splitting filter, an efficiency of 5.5% is experimentally obtained with a minimum bandgap of 1.05 eV. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A new silicon MEMS process has been proposed utilizing anodic bonding of an extremely thin silicon film (60 m) on a glass substrate, followed by photo lithographically defining micro spring structures on the silicon film and dry etching the silicon film using an inductively coupled plasma (ICP) dry etcher. After that, the underneath glass was selectively etched off using a hydrofluoric (HF) solution to release the micro spring. This technique was successfully applied to a micro vibration detection sensor with the silicon microspring with a cross section of 10 m x 60 m with a length longer than 500 m.

Thin film organic transistors with Si/SiO2 (300 nm)/pentacene (70 nm)/Au and Si/polyimide (320–690 nm)/pentacene (70 nm)/Au structures have been fabricated and their performances have been compared. The evaluated mobility of the holes of the SiO2 transistor was 0.002 cm2/Vs, while those of the polyimide transistors were between 0.026–0.031 cm2/Vs. On the other hand, the threshold voltage of the SiO2 transistor was −15 V, while the threshold voltages of the polyimide transistors were approximately +4 V independent of the polyimide thickness. This apparently strange behavior of the polyimide transistors might be attributed to some more negatively charged species accumulating at the polyimide/pentacene interface as the thickness of the polyimide film increases. The PI films had a significantly low level of the leakage current, and the estimated gate-drain leakage current of the corresponding transistor at the gate voltage of −100 V is estimated to be negligibly small compared with the source-drain current.

Near-field radiation that has a high intensity of electric field was applied to enhance conversion from thermal energy to electricity in a wavelength range less than 1.1 μm or 1.8 μm. A commercial Si-photovoltaic cell and a thermophotovoltaic cell made of GaSb semiconductors were used to confirm that the near-field radiation effect (the evanescent wave effect) can be applied to enhance generation of electricity. As a result, an increase in output power generation of electricity by the evanescent wave effect was detected and the short-circuit current density increased about 1.3 times for the Si-PV cell and 3.0 times for the GaSb-TPV cell as larger than those obtained by the conventional propagating-wave radiation.Copyright © 2011 by ASME

We fabricated pentacene OTFTs with chemically modified SiO2 surface by phenyltrichlorosilane (PTS), and studied the molecular ordering of the pentacene films and electrical characteristics of the OTFTs. The molecular ordering of the pentacene thin film was improved by PTS treatment. We also fabricated organic thin film transistors with phenyltrichlorosilane treatment. The carrier mobility of the transistor with PTS treatment was 3.7 × 10−2 cm2/Vs, it was larger than that of the transistor without PTS treatment (2.0 × 10−2 cm2/Vs). We believe that this improvement of the μ value was due to improvement of the molecular ordering by PTS treatment.