In Situ Irradiation and Measurement of Triple Junction Solar Cells at Low Intensity, Low Temperature (LILT) Conditions

The performance of triple junction InGaP/(In)GaAs/Ge space solar cells was studied following high energy electron irradiation at low temperature. Cell characterization was carried out in situ at the irradiation temperature while using low intensity illumination, and, as such, these conditions reflect those found for deep space, solar powered missions that are far from the sun. Cell characterization consisted of I-V measurements and quantum efficiency measurements. The low temperature irradiations caused substantial degradation that differs in some ways from that seen after room temperature irradiations. The short circuit current degrades more at low temperature while the open circuit voltage degrades more at room temperature. A room temperature anneal after the low temperature irradiation produced a substantial recovery in the degradation. Following irradiation at both temperatures and an extended room temperature anneal, quantum efficiency measurement suggests that the bulk of the remaining damage is in the (In)GaAs sub-cell.

I. Introduction

A Number of space missions have been, or are being, designed to be powered by space solar cells but are farther away from the Sun than the Earth/Mars region where most of the previous use of these cells has taken place. These greater distances from the sun will result in the cells operating at low intensity and low temperature (LILT) conditions. A question that arises is one of whether the extensive data previously taken following room temperature irradiation adequately describes the LILT irradiation response. Several studies have been published that subject state-of-the-art space solar cells to one or more of the aspects of these conditions, but none covers the conditions completely.