Simulating the operation of silicon photovoltaic cells at outer space environments

Abstract

All solar cells that are developed for use in space must take into consideration the unique aspects of the space environment. The spectral illumination that is available in space is not filtered by our atmosphere and thus is different from what is experienced on Earth. In this concern, a study was conducted to evaluate the performance of silicon photovoltaic systems exposed to isotropic irradiation, protons and electrons, which approximate the space irradiation effects. Also, the study extended to include the operation of such devices at extreme low temperatures down to cryogenic levels. Significant degradation was experienced in the silicon cells output characteristics after bombardment with either protons fluence (10¹⁴ to 10¹⁶ p/cm²) within the energy range from 0.6 to 6.0 MeV or electron fluencies up to 1.0 × 10¹³ electron/cm² at energies up to 12.0 MeV. For low energy protons (from 0.6 MeV to 2.0 MeV), the damage rate per particle decreases as the energy increases. The decrease is approximately inversely proportional to particle energy. At higher energies (up to 6.0 MeV) the damage level is almost constant. Also, for the case of electron irradiation, the damage rate is shown to decrease the open circuit voltage, and the short circuit current. Consequently, this decreases the output power. On the other hand, the short circuit current was shown to be un-sensitive function of temperature, where for the temperature range from +300°C down to -160°C, a rate of current decrease of 6.42 µA/°C was reported. The main variation was observed to be due to open circuit voltage, where for the same temperature range, a rate voltage increase with 1.90 mV/°C was recorded. Finally, the cell output power was shown to increase, within the temperature range, at rate of 15.64 µW/°C.

Keywords: Solar cells, protons, electrons, low temperature, space environment.