No abstract

A short-circuit current density (Jsc) of a spherical Si solar cell with a reflector cup has been calculated as a function of light concentration ratio, defined as the aperture area of the reflector cup divided by the projection area of the spherical Si solar cell, and incidence angle using a three-dimensional ray-tracing simulation. The calculation results show that the Jsc values of 39.7, 38.4, and 38.1 mA/cm2 can be obtained with the light concentration ratios of 4, 6, and 8, respectively, indicating that a higher concentration ratio reduces the optical efficiency of the reflector. Also, these results indicate that Jsc approaching 40 mA/cm2 can be realized without surface texturing in the spherical Si solar cell. Even in a high light concentration ratio of 8, a relatively high Jsc exceeding 37 mA/cm2 can be obtained for the incidence angles of 0–10°, indicating that the amount of spherical Si can be reduced effectively by the reflector cup.

An optimum design of an antireflective (AR) coating for a spherical Si solar cell with a reflector cup has been analyzed with a three-dimensional (3D) ray-tracing simulation. The 3D ray tracing is required to estimate the short-circuit current density (J sc) because of an incident light angle distribution on a solar cell surface. In the simulation, the solar cell consists of a spherical Si solar cell with a diameter of 1 mm covered by an AR coating without surface texturing, and a hemispherical reflector cup with an aperture of 2 mm. The calculations of AR coating thickness (t) and refractive index (n) dependences on J sc revealed that an optimum J sc of 39.7 mA/cm2 can be obtained at t=78 nm and n=2.0. Also, a higher design tolerance in an optical film thickness of the AR coating is demonstrated, which is especially advantageous for spherical Si solar cells which inherently have some technical difficulties in a uniform AR coating formation.