Abstract
Bilateral solar cells can convert albedo light (sunlight reflected from the earth) incident on the back side of the cell to improve the power to weight ratio of satellite arrays operating in Low Earth Orbits. However, the high energy radiation trapped in the Van Allen Belt surrounding the earth limits the possible improvement of solar cell electrical output by degrading the minority carrier diffusion length. The purpose of this work is to design cells to be able to collect efficiently albedo-generated carriers at end-of-life(EOL). The FORTRAN program Solar Cell Analysis Program in Two Dimensions is used to model four cell geometries for base resistivities of 1.0 to 1240. Ω—cm. The EOL efficiencies and normalized output power are compared for all cells. All the thicker (250. micron) cells modeled peak in performance within the 10.-40. Ω—cm base resistivity range both with and without albedo illumination. It is found that alternative geometries to the standard solar cell can be used to better collect albedo-generated carriers at EOL. The etched multiple vertical junction cell(22%) and the 50. micron thick standard cell(45%) show the most improvement in normalized output power over the best one- sun illuminated standard cell. Albedo light is modeled as 40. milliwatts /cm2 (AMI.5 spectrum), or 30% of one sun AM0.0 incident power. Values for the damage coefficient, Kj, are found in the literature for irradiation by 1.0 MeV electrons. Radiation induced degradation is modeled by SCAP2D through degradation of the minority carrier lifetimes. Solar cell output parameters are compared for four cells, the standard cell (for varying thicknesses), the etched multiple vertical junction cell, and the tandem junction cell. The physical phenomena responsible for poor cell performance at EOL are discussed.
Date of this Version
12-1-1987
Comments
Supported by NASA-Lewis Research Center Grant #NAG 3-657.