Y. Nitta

A new type of amorphous silicon photovoltaic cell generating more than 2.0 V

A new type of plasma‐deposited amorphous silicon photovoltaic cell having a horizontally multilayered p‐i‐n unit‐cell structure has been developed. The open‐circuit voltage Voc is nearly proportional to the number of repetitions of the p‐i‐n unit cell. Almost‐constant energy‐conversion efficiencies of around 4% have been obtained with Voc ranging from 0.6 to 2.4 V by applying a simple optimum design rule to the cell‐construction parameters.

Device physics and design of a-Si ITO/p-i-n heteroface solar cells

Abstract Effects of doped impurities on electrical, optical and optoelectronic properties in amorphous hydrogenated silicon (a-Si:H) films have been investigated. Doped and undoped a-Si:H films were prepared by plasma deposition from monosilane diluted with hydrogen containing a preset amount of phosphine or diborane as a dopant gas. A series of systematic data on the relation between preparation conditions, particulary substrate temperature and hydrogen content, photoconductivity, absorption coefficient, etc., and also solar cell design parameters are presented. Device physics and optimum design for the heteroface solar cell are discussed. On the basis of these data, ITO/p-i-n heteroface solar cells have been fabricated. At the present stage of the experiments, a power conversion efficiency of 4.5% is obtained under a sunlight of 80 mW/cm2. The junction structure and its technology would be valuable for the fabrication of low cost solar cells of large area.

Glow discharge produced amorphous silicon solar cells

Abstract A series of basic investigations on the glow discharge produced amorphous silicon (GDa-Si) and its interface properties aimed for the low cost solar cells has been carried out. The fabrication technique to make wide area and uniform films is presented, and the optical and photovoltaic properties of GDa-Si are also discussed. In the present stage of our experiments, a conversion efficiency of as high as 4.5% has been achieved in an ITO/p i n cell for AMI sunlight. This type of solar cells may have a possibility to improve their photo-voltaic performances by the optimum design on the solar cell structure.

Effect of DC electric field on the basic properties of RF plasma deposited a-Si

Abstract Effect of dc electric field superimposed perpendicularly to the rf electric field during the plasma deposition has been studied. A series of basic investigations on the manner hydrogen incorporated, optical and photoconductive properties have been made as functions of deposition parameters. A clear difference in the film quality was observed with the polarity of dc electric field. Noticeable results obtained are enlarged absorption coefficient and photoconductivity in the films deposited with positive dc electric field.

Gap states in undoped amorphous silicon studied by below-gap modulated photocurrent spectroscopy

Abstract The energetic distribution and nature of dangling-bond states in undoped a-Si: H have been investigated by a newly developed gap-state spectroscopy which is based on the frequency-resolved spectrum of modulated photocurrent with below-gap photoexcitation. The energy scale is directly specified by the energy of the below-gap light populating the particular gap states. The result has led to the conclusion that the peak of the gap-state distribution associated with doubly occupied dangling bonds (D-) is located about 0•5 eV below the conduction band edge. The analysis for the pre-exponential factor of the thermal emission rate of electron from the D- centre suggests that the emission occurs in two stages through excited states.

Energetic distribution of dangling bond states in undoped amorphous silicon

Abstract Frequency-resolved modulated photocurrent spectroscopy has been introduced to investigate the gap states distribution in undoped a-Si:H. The result shows that the D− centre has a near-Guassian distribution centered at about 0.5 eV below the conduction band edge. The deduce DOS exhibits characteristics structures including the D− centre over a wide range of the energy band gap.

Study of gap states in a-SiGe:H alloy system by below-gap modulated photocurrent spectroscopy

Abstract The gap-state distribution associated with dangling bond defects in a-SiGe alloy system has been investigated by below-gap modulated photocurrent spectroscopy. Si- and Ge-related D− states have been separately observed for the first time, the energy locations of which designate close correlations with the band gap energy.

Design Parameters of a-Si: H High-Voltage Photovoltaic Cells

An optimum design for the amorphous silicon high-voltage photovoltaic cells composed of horizontally multi-layered p-i-n cells has been studied. A series of technical data on the design parameters and the device physics for the multi-layered cell are presented. Newly designed cell shows the open circuit voltage Voc nearly proportional to the number of unit p-i-n junction with almost constant conversion efficiencies of around 4%. Attempts have been made up to ten p-i-n layered cells with a Voc of 4.5 volts. Another new performance as an arbitrary spectral photosensor having a structure of double p-i-n junctions is proposed.

Horizontally multi-layered a-Si photo-voltaic cells A new type of high voltage photo-voltaic device

Abstract A new type of plasma-deposited amorphous silicon photovoltaic cell having a high out-put voltage has been developed. Structure of the new devices is a horizontally multilaminated p-i-n unit cell with a indium-tin-oxide heteroface window expressed as a conventional symbols of ITO/(p-i-n)m/SS. The open-circuit voltage Voc is nearly proportional to the number of repititions of around 4% have been obtained with Voc ranging from 0.6 to 2.4 V by applying a simple optimum design rule to the cell-construction parameters.

P-Channel Polycrystalline Silicon Thin-Film Transistors on Glass Substrates

A p-channel polycrystalline silicon thin-film transistor was fabricated at low temperature (<600°C) on a glass substrate for application to large-area display devices with CMOS peripheral circuits. An active layer was formed by laser crystallization of amorphous silicon film using a liquid encapsulation technique to increase the grain size. The gate insulator and source and drain contacts were made by plasma-enhanced chemical vapor deposition. A hole mobility of 43 cm2/(V s) was obtained by these methods.