Masashi Yoshimi

Photocurrent multiplication in a hydrogenated amorphous silicon‐based p‐i‐n junction with an a‐SiN:H layer

Photocurrent multiplication has been observed in a hydrogenated amorphous silicon‐based p‐i/a‐SiN:H/i‐n structure junction under a reverse biased condition. A systematic investigation on the photocurrent characteristics in this junction system has been carried out. It has been shown from the analysis of the results that multiplication arises from the interband tunneling injection of valence band ‘‘electron’’ through the a‐SiN:H barrier layer. A device modeling on the basis of the experimental data permits us to design the device structure for achieving better performances. As a preliminary optimization of device structure, an external quantum efficiency exceeding 70 has been obtained under the operation voltage 30 V in the heterojunction photodiode having an a‐SiN:H (thickness of 40 nm with optical energy gap 2.1 eV) at the p a‐SiC:H/i a‐Si:H interface. The proposed highly sensitive photomultiplier device might have a wide variety of application fields such as a solid‐state imager for high‐definition tele...

Toward 20% Efficiency With a-Si // poly-Si Tandem Solar Cell

A series of experimental investigations has been made on the a-Si // poly-Si tandem solar cell which is one of the most promised candidate of high cost-performance photovoltaic cell, e.g., high efficiency, low cost with almost no light induced degradation. Employing high conductivity with wide optical band gap p type microcrystalline SiC (μ-SiC) as a window material together with a-SiC as an interface buffer layer and also n type μc-Si as a back ohmic contact layer in the poly-Si based bottom cell, the conversion efficiency of 17.2 % has been obtained. Combining an optically transparent a-Si p-i-n cell as a top cell with an optical coupler between the top and the poly-Si bottom cell, a total efficiency of 20.3 % has been obtained so far on the four-terminal stacked mode structure. A systematic technical data for the optimization of cell structure variation on the developed tandem solar cells are presented and further possibility to improving the performance are discussed.

Approaching 20% efficiency with a-Si/poly-Si tandem solar cell

A high-efficiency a-Si/poly-Si four-terminal tandem solar cell has been developed. By the optimization of each layer thickness and optical features of the top and bottom cells, the authors obtained a conversion efficiency of 19.1% with a good stability and repeatability. There appears to be a possibility of achieving conversion efficiency exceeding 20% with the four-terminal tandem device through careful optimization of the a-Si top cell and optical matching between the two cells.<<ETX>>

Observation of tunneling assisted photocurrent multiplication in a SiN/a-Si heterojunction

Photocurrent multiplication has been observed in a-Si:H basis p/a-SiN/i/n junction photocells. As a result of optimizations of the device structure, an external quantum efficiency exceeding 70 has been obtained so far under the reverse biased operation voltage 30V. From a systematic investigation of the photocurrent characteristics, it has been inferred that the excess component of the current arises from the real-space interband tunneling across the a-SiN:H layer.

Improvement of blue-light emission in amorphous carbon based electroluminescent device

Electroluminescent devices consisting of amorphous SiN/C/SiC/C/SiN multilayered structure has been studied to approach an intense blue emission. Upon optimization of geometrical configuration as well as band-gap combination of the multilayers, a luminance exceeding 30 cd/m 2 has been attained with an emission spectrum sharply peaked at 2.5 eV. Physical meaning of the improvement is discussed in association with EL operation mechanism characteristic to amorphous materials.

Analysis of one‐line ground fault surge on simulated overhead distribution line

One-line fault location techniques of intermittent ground fault points on nongrounded distribution lines are necessary to supply steady electric power for customers. This paper proposes a novel method that uses frequency spectra of transient waveforms at a sending end when an intermittent ground fault occurs. In this method, if a ground fault position differs, it causes a different frequency spectrum pattern for the current or voltage transients at a send end (decided by surge reflection phenomena between the sending end and the ground fault point). Comparison between experimental data of one-line ground fault tests on a simulated overhead line (373 m line length, two branch points) and digital simulation analyses shows that the grounded capacitance of a power source transformer was useful in locating the ground fault point.