Wataru Shinohara

Development of high-voltage photovoltaic micro-devices for an energy supply to micromachines

A submodule of photovadtaic micro-devices which generates more than 200 volts with an area of 1 cm2 has been developed to directly drive piezoelectric or electrostatic actuators which will be used as microactuators. The submodule consists of 95 micro cells ( unit cell size : about 0.5 m m x 2.0 mm ) interconnected in series, and produces a submodule open circuit voltage (Vac) of 207 volts, short circuit current (Isc) of 36.6p A, maximum output power (Pmax) of 4.65mW and fill factor (F.F.) of 0.615 under Air Mass ( A M ) 1 . 5 , 100mW/cmz illumination. Each micro cell has aln a-Si triple stack construction and produces V,, of 2.3 volts, and short circuit current density (Jsc) of 6.5 mA/cm2. The series connection for the micro cells is precisely processed by a focused laser beam, thereby significantly reducing the invalid area of the submodule. To evaluate the use of this submoduleas a microactuators power source, i t was confirmed tlhat a piezoelectric polymer could be directly driven by the electrical output of the submodule. 1. I NTR 0 DUCTI <IN Recently several energy supply methods for micromachines, such as the microwave, photon and microbattery energy supply, have been investigated. Among them, the photon energy supply is the most suitable as an energy supply for micromachines because of the following advantages; (1) Wireless energy supply (2) Simultaneous supply for plural micromachines (3) Applicable both in water and in air (4) Semipermanent operation under photon energy (5 ) Suitable for producing a high voltage On the other hand, many different types of actuation principles have been proposed for the micromachines actuator. However, most of this work has focused on electrostatic[l] or piezoelectric drives[2]. Although some work has been done to decrease the electric voltage requirement, electrostatic or piezoelectric actuators usually require a drive voltage ranging from tens to hundreds of volts. In order to meet this energy requirement for actuators, the energy source must be developed to generate a correspondingly high-voltage in a small area. Concerning the photon energy supply, J.B. Lee et al have already reported a high-voltage solar cell array which generates 150 volts in 1 cm2 [ 31. However, the efficiency of the solar cell array is not very high (less than 0.2 %). We have newly applied a laser processing technique to the fabrication of photovoltaic microdevices. As a result, we have developed high-voltage photovoltaic micro-devices which generate more than 200 volts with an area of 1 cm2 and offer very good output characteristics. This paper describes the structure, the fabrication process and the characteristics of the high-voltage photovoltaic micro-devices and the development of the laser micro-processing technique. An actuation demonstration using this devices to drive a piezoelectric actuator is also described. 2.HIGH-VOLTAGE PHOTOVOLTAIC MICRO-DEVICES 2.1 Structure The energy source for micromachines should satisfy two requirements at the same time. (1) Generate high enough voltage to drive an electrostatic or piezoelectric actuator (2) Take up a small area In order to meet these requirement, we decided the following design criteria.

Applications of laser patterning to fabricate innovative thin-film silicon solar cells

In view of the need to obtain high-efficiency and low-cost photovoltaic power generation systems, the electrical series connection of multiple solar cells by laser patterning is a key issue for thin-film silicon solar cells. For a series connection with no thermal damage to the photovoltaic layers, a theoretical analysis of glass-side laser patterning, in which a laser beam is irradiated from the side of a glass substrate, and the optimization of the structure of the solar cells are conducted for a-Si:H/a-SiGe:H stacked solar cells deposited on glass substrates. As a result, an a-Si:H/a-SiGe:H module with both a large area (8,252 cm2) and a conversion efficiency of 11.2% is obtained. Then, to improve efficiency and to reduce cost, the minute structure of microcrystalline silicon (μ c-Si:H) and film-side laser patterning, in which a laser beam is irradiated from the side of the deposited film, are investigated for a-Si:H/μ c-Si:H stacked solar cells deposited on insulator/metal substrates. It is proved that the discontinuity of the doped and photovoltaic layer may cause a reduction in the path density of the leak current, and that this contributes to an improvement in the efficiency of the solar cells. Based on the developed structure, an initial efficiency of 12.6% is obtained in a small-size solar cell. An a-Si:H/μ c-Si:H module (Aperture area = 56.1cm2) with three segments has also been fabricated with an initial efficiency of 11.7% as a first try.

The Development of High-Rate Deposition Technology for Microcrystalline Silicon for High-Efficiency a-Si/μc-Si Tandem Solar Module

A localized plasma confinement chemical vapor deposition (LPC-CVD) method with special cathode structures was proposed to solve problems of stability and uniformity of plasma under high pressure (>;1000 Pa). The initial conversion efficiency achieved by LPC-CVD for an a-Si/μc-Si tandem solar cell was 10.4% (1 cm2) for a 550 × 650 mm2 substrate at the deposition rate of 2.2 nm/s. Since then, we have been developing high-rate deposition technology for 1100 × 1400 mm2 substrates (Generation 5.5 (G5.5) size). A-Si/ μc-Si tandem solar modules have been achieved with an efficiency of 11.1% (initial) and 10.0% (stable) and a deposition rate of 2.4 nm/s on a G5.5-size substrate.

Progress in the development of high-conversion-efficiency a-Si/μc-Si tandem solar module using μc-Si thin film with high deposition rate on Gen. 5.5 large-area glass substrate

The technology to make high-quality, high-reliability solar modules with a high deposition rate for μc-Si thin-film is a problem for the industrialization of low-cost, high-conversion-efficiency a-Si/μc-Si tandem structure solar modules. Sanyo has solved this problem by developing an original CVD technique called Localized Plasma Confinement CVD and a new evaluation method for μc-Si thin film. A stabilized conversion efficiency of 10.0% was achieved for an a-Si/μc-Si tandem structure solar module, and a deposition rate of 2.4 nm/s for μc-Si thin-film was attained on a Gen. 5.5 full-size glass substrate. To obtain a higher conversion-efficiency a-Si/μc-Si tandem structure solar module, fundamental studies of μc-Si thin-film have been performed, and a stabilized conversion efficiency of 10.5% (Initial solar module conversion efficiency: 12.0%) has been achieved on a large-area glass substrate. Furthermore, in the study of this development, the highest stabilized conversion efficiency of 12.0% (Initial conversion-efficiency: 13.5%) was attained. Module reliability tests confirmed by IEC 61646 Ed. 2 revealed that the performance of the module is adapted. These high-performance a-Si/μc-Si tandem structure solar modules were prepared by using the knowledge of our thin-film and module technologies.

Progress of SANYO's R&D on thin film silicon solar module

We have been developing original technologies for Localized Plasma Confinement (LPC) CVD method. LPC-CVD method achieves both a high deposition rate and a high conversion efficiency. From the results of IR analysis and Raman spectroscopy for µc-Si i-layer thin films, it was suggested that the combination of high stretching mode fractions in IR spectra and Raman crystallinity may have a correlation with the conversion efficiency of a-Si/µc-Si tandem cells. An R&D line for processing a-Si/µc-Si solar modules on G5.5 size glass substrates (1100 × 1400 mm2) has been constructed. Module efficiency of 11.1% (Initial) and 10.0% (Stable) has been achieved with a film deposition rate for the µc-Si i-layer of 2.4 nm/s on a G5.5 size substrate.

Stabilized 9% efficiency of large-area (/spl sim/5000cm/sup 2/) a-Si/a-SiGe tandem submodules using high-rate deposition

High-rate deposition of photovoltaic layers of a-Si/a-SiGe tandem solar cells has been investigated using RF (13.56 MHz) plasma-CVD method while keeping the substrate temperature below 200/spl deg/C. A remarkable improvement in film quality and device performance can be attained at a high deposition rate of /spl ges/3 /spl Aring//s by optimizing hydrogen dilution and other deposition conditions. It is of great importance to utilize the effect of hydrogen dilution which can reduce the incorporation of excess hydrogen in the films. The worlds highest stabilized efficiency of 9.3% has been achieved for a large-area (5150cm/sup 2/) a-Si/a-SiGe tandem submodule whose top and bottom photovoltaic layers are deposited at /spl sim/3 /spl Aring//s using an optimized hydrogen dilution. A smart back reflector, with a high light scattering effect, and other approaches to enhance the optical confinement effect, are also proposed for further improvement of cell performance.