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Development of InGaAsN solar cells and characterization of their degradation in space radiative environment

Maxime Levillayer 1, 2 
1 LAAS-PHOTO - Équipe Photonique
LAAS - Laboratoire d'analyse et d'architecture des systèmes
Abstract : The current development of artificial satellites used for telecommunication, scientific and military applications, requires the conception of powerful and reliable electrical sources that can be used in a space environment. On-board systems rely predominantly on photovoltaic conversion and more specifically on multijunction solar cell (MJSC) technology. The standard MJSC structure used in space applications is the triple junction GaInP/(In)GaAs/Ge. In order to increase further the efficiency of this MJSC, it is necessary to optimize photon harvesting in the near infrared region. This can be achieved by replacing the germanium subcell by a subcell with a 1 eV bandgap energy. Even higher efficiencies can be obtained if the 1 eV subcell is integrated within a four-junction architecture. For its integration to be possible, this 1 eV subcell needs to be based on a material with the same lattice parameter as GaAs or Ge. It also needs to photogenerate more than 15 mA/cm² under integration condition and it should exhibit high radiation hardness to enable long lifespan space missions. In the framework of this thesis, we have developed solar cells based on the InGaAsN quaternary to fulfil all these requirements. We have grown solar cell structures and InGaAsN bulk layers by molecular beam epitaxy (MBE). Through multiple material characterizations, we have studied the impact of the growth conditions on the optoelectronic properties of InGaAsN. InGaAsN solar cells were fabricated through clean room technological processing steps (lithography, metallisation, etching). These solar cells were then characterized with current-voltage and quantum efficiency measurements. In MJSC integration conditions, our device could generate current densities as high as 8 mA/cm². Increasing the nitrogen content and the thickness of the absorber would lead to higher photocurrents enabling current-matching in the MJSC. The integration of an InGaAsN subcell within a GaAs/InGaAsN tandem structure was also demonstrated. InGaAsN solar cells and samples dedicated to photoluminescence (PL) and deep level transient spectroscopy (DLTS) analysis were then irradiated with 1 MeV electrons and protons. Comparing the InGaAsN material properties and the solar cell characteristics before and after irradiation allowed us to evaluate the degradation rate of InGaAsN cells. These solar cells exhibit a radiation hardness towards electrons and protons greater than their GaAs counterparts.
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Submitted on : Thursday, December 16, 2021 - 3:05:02 PM
Last modification on : Friday, June 3, 2022 - 3:24:01 AM
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Maxime Levillayer. Development of InGaAsN solar cells and characterization of their degradation in space radiative environment. Micro and nanotechnologies/Microelectronics. ISAE - Institut Supérieur de l'Aéronautique et de l'Espace, 2021. English. ⟨tel-03483437⟩

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