Abstract
The degradation of individual subcell J-V parameters, such as short circuit current, open circuit voltage, fill factor, and power of a GaInP/GaInAs/Ge triple junction solar cell by 1 MeV electrons were derived utilizing the spectral reciprocity relation between electroluminescence and external quantum efficiency. After exposure to a fluence of 1 × 1015 1 MeV electrons, it was observed that up to 67% of the voltage loss is from the middle, GaInAs subcell. Also, the dark saturation current of the Ge and GaInAs subcells increased but a simultaneous decrease in ideality factor caused a reduction of the open circuit voltage. The reduced ideality factor further indicates a change in the primary recombination mechanism.
Highlights
Understanding the effects that influence the currentvoltage (I-V) characteristics of space photovoltaics is critical to predicting their on-orbit performance[1-3]
By taking electroluminescence spectra of each junction in a multijunction solar cell at different injection currents you can calculate the voltage of each subcell at each injection current
The open circuit voltage of each subcell is derived from the voltage calculated using Eq 1 at an injection current equal to the short circuit current of the individual subcell
Summary
Understanding the effects that influence the currentvoltage (I-V) characteristics of space photovoltaics is critical to predicting their on-orbit performance[1-3]. By investigating the effects of space radiation on the underlying device parameters we can better understand and predict the performance of on-orbit solar arrays. While current degradation can be tuned for and characterized by quantum efficiency measurements, it has only been recently discovered that the open circuit voltage of each subcell of a monolithic GaInP/GaInAs/Ge can be derived along with the partial dark and light currentvoltage parameters. By utilizing the reciprocity theorem between electroluminescence and external quantum efficiency [5], the subcell dark and light current-voltage curves can be derived before and after irradiation [6-8]. The ability to measure all the degradation current-voltage parameters of each subcell can lead to better degradation modelling. Understanding how each subcell degrades in voltage adds a new dimension of potentially tuning for less voltage degradation after particle irradiation
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