Tatsuo Saga

Progress and future view of silicon space solar cells in Japan

The progress and the future view of silicon (Si) space solar cells in Japan are reviewed. In 1991, two types of the high-efficiency silicon (HES) cell were developed: (1) NRS/LBSF cell; (2) NRS/BSF cell. The former shows a conversion efficiency of 18.0% (AM0, 28/spl deg/C) at beginning-of-life (BOL), the latter shows superior radiation tolerance. In 1998, the radiation tolerance of the NRS/BSF cell was improved; moreover, the advanced high-efficiency silicon-1 (AHES-1) cell was accomplished. It shows 13.1% at end-of-life (EOL). The development has progressed to make the 13.7% EOL cell: AHES-2 cell. In 1994, the integrated bypass function (IBF), which prevents failures due to reverse biasing of cells, was proposed. The NRS/BSF cells with IBF have been used already on several satellites. The structures, performance, and radiation tolerances of these cells are introduced. New approaches for further improvement are proposed.

Radiation Test of Silicon Solar Cells for Space Application

The degradation of electrical performance due to electron, high energy proton, and low energy proton irradiations was investigated for various space qualified modern solar cells. Electrical performance data taken under AMO/28°C conditions on the irradiated and annealed cells showed that conventional (Conv.) and BSR cells are the least sensitive to damage under high energy particle (electron and proton) irradiations. Black cells were more tolerant to the high energy particle irradiations than BSF cells, and showed the most excellent electrical performance among all types of solar cells after heavy irradiations. Covered cells (Black and BSFR cells) were irradiated with low energy protons. The Voc and Isc degradations of the cells could hardly be found, while the Pmax degradations were about 5%.

Development of high efficiency thin silicon space solar cells

The improvement of the efficiencies of thin silicon solar cells for space use was studied. The representative 3 types of nonreflective surface structures were evaluated and their characteristics were clarified. Solar cells with these structures showed excellent electrical performance and the best result of 18.0% efficiency for 100 /spl mu/m thick cells was attained. Cells made from 2 /spl Omega/ cm substrates showed higher electrical performance and radiation hardness than those from 10 /spl Omega/ cm substrates. The electron irradiation tests showed that the current degradation of the cells with lower resistivity substrates were reduced and the improved solar cells can be used for future satellites.<<ETX>>

Electrical properties of thin silicon space solar cells

Abstract Thin silicon solar cells with a Non-Reflective front Surface (NRS), a passivated rear surface and locally diffused BSF structure have been considered to be hopeful candidates as space solar cells of the next generation. In this paper, the electrical properties of textured surface cells and flat (non-textured) surface cells are compared and the surface recombination velocity S e of these cells are discussed. Then, the electrical properties of 10 Ω cm substrate cells and 2 Ω cm substrate cells are compared and the carrier recombination at the rear Si/SiO 2 interface is discussed using energy band diagrams.

High efficiency silicon solar cells for space use

High-efficiency silicon solar cells for space use were developed, and the manufacturing process was established. The maximum size of these cells is 4*6 cm. The cells have fine grid patterns formed by photolithography and the lift-off technique. Obtained AM0 efficiencies of 50, 70, and 100 mu m-thick 4*6 cm BSFR cells at 28 degrees C were 14.3%, 14.5%, and 14.8%, respectively. Those of 200 mu m BSR cells with 10 Omega -cm substrate and 2 Omega -cm substrate were 12.7% and 13.6%, respectively. Work to increase the electrical output of these cells is discussed. At present nontexturized 100 mu m cells show 16.1% and texturized 200 mu m cells show 17.3%.<<ETX>>

Development of both-side junction silicon space solar cells

This paper reports the recent results of improving the radiation hardness of silicon solar cells, which is SHARP and NASDAs project since 1998 (Tonomura et al., Second World Conference on Photovoltaic Solar Energy, 1998, pp. 3511-3514). Newly developed 2 x 2 cm 2 Si solar cells with ultrathin substrates and both-side junction (BJ) structure showed 72.0 mW (13.3% efficiency) maximum output power at AMO, 28°C after 1 MeV electron irradiation up to 1 x 10 15 e/cm 2 and the best cell showed 72.5 mW (13.4%) maximum output power. These solar cells have p-n junctions at both front and rear surfaces and showed less radiation degradation and better remaining factor than previous solar cells.

Development of high efficiency silicon space solar cells

The cell design and manufacturing process for the high efficiency thin silicon space solar cells (call NRS/LBSF cell) were finalized and their characteristics were qualified. The 100 /spl mu/n NRS/LBSF cells showed efficiencies of maximum 18.5% and average 18.0%. After electron irradiation of 1E+15e/cm/sup 2/, the NRS/LBSF cell showed about 1.2 times higher output power than the conventional 200 /spl mu/m BSR cell.

New silicon space solar cells with IBF (integrated bypass function)

New silicon space solar cells with IBF (integrated bypass function) which enable prevention of a failure caused by a reverse biasing are proposed. To investigate the feasibility of these cells, some preliminary experiments were performed. From the results of these experiments, it is confirmed that these cells have no problems intrinsically as space solar cells and contribute to obtaining higher reliability of a solar array.

History of contribution of photovoltaic cells to telecommunications

Since 1959 Sharp Corporation has been devoted to commercializing photovoltaic-cells (PV-cells) for public, industrial, and residential applications. The cumulative production volume reached to 2GW in 2007 for the first time in the world, and the annual production capacity grew to 710MW in 2009. The present article outlines Sharps history of commercializing PV-cells, focusing on their applications to terrestrial and space telecommunications, on the occasion of having received the IEEE Milestone for commercialization and industrialization of PV-cells in April 2010.

Ultrathin Silicon Solar Cell for Space Application

Ultrathin silicon (Si) solar cells for space application were fabricated on an experimental basis and the electrical characteristics were investigated for three kinds of cells (Black, BSFR and Conventional cells). Under 135.3 mW/cm2 (AMO) illumination, ultrathin Black cells showed 67.7 mW output, which is equal to 89% output of 280 µm Black cells. The power to mass ratio of bare ultrathin Black cells was 3.6 times high compared with 280 jum thick Black cells. 1 MeV electron irradiation test was carried out to evaluate the radiation resistance. Ultrathin cells showed superior radiation resistance compared with that of 280 µm thick cells, and it was comparable to that of a GaAs solar cell which had been recognized as a radiation resistive cell. Our experiments suggest that the ultrathin solar cells have high potential to be used for space application.