PREDICTION OF SPACE DEGRADATION OF MULTIJUNCTION SOLAR CELLS GESEC R&D Inc. Semiconductor Materials Engineering PREDICTION OF SPACE DEGRADATION OF MULTIJUNCTION SOLAR CELLS J. C. BOURGOIN, S. MAKHAM & G.C. SUN GESEC R&D, 68 av. de la forêt, 77210 Avon, FRANCE .

 = 71 /Enl (eV.cm-1) , ( in cm-2) A – Semi-empirical method For GaAs:  = 71 /Enl (eV.cm-1) , ( in cm-2)

Experimental verification Using GaAs cell NASA data (proton energies from 0,2 to 9,5keV)*: Standard: the degradation curve of Pm corresponding to 1 MeV electron irradiation. (*) B.E. Anspaugh Solar Cell Radiation Handbook, JPL Pub, (1996).

B – Non empirical method 1-Classical calculation of the current-voltage characteristics of each subcell knowing the minority carrier lifetimes τ of the base and emitter for a given fluence φ: 1/= 1/0 + k k: Introduction rate   n & p : Capture cross sections of minority carriers  2- Construction of the degradation of the MJ cell from that of each subcell i: Isc(φ) = minimum (Isci (φ)) Voc (φ) = i (Voci(φ))

Experimental verification Case of a GaInP/GaAs cell (Emcore):

Necessary knowledge, for both base and emitter for each subcell k, introduction rate (or concentration kφ). σb, σe, minority capture carrier cross section. τ0e, τ0b, initial lifetimes. thicknesses . Recombination velocities at interfaces. alloy composition x. Techniques to determine these parameters: k  DLTS, I-V in dark, electroluminescence. x  Low temperature electroluminescence. τ0e,b  I-V under illumination.

Prediction of degradation (2J Emcore)

Determination of k versus energy