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This paper reports the recent results of improving the radiation hardness of silicon solar cells, which is SHARP and NASDA's project since 1998 (Tonomura et al., Second World Conference on Photovoltaic Solar Energy, 1998, pp. 3511–3514). Newly developed 2×2 cm2 Si solar cells with ultrathin substrates and both-side junction (BJ) structure showed 72.0 mW (13.3% efficiency) maximum output power at AM0, 28°C after 1 MeV electron irradiation up to 1×1015 e/cm2 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.

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.

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. >

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.

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%. >