(GaAl)As Tuneel junctions grown by molecular beam epitaxy: Intercell ohmic contacts for multiple-band-gap solar cells

Intercell ohmic contacts (IOCs) formed from heavily doped junctions in Ga0.15Al0.85As have been grown by molecular beam epitaxy with GT values from 24 to 42 Ω−1 cm−2. The electrical and optical losses in (GaAl)As IOCs have been evaluated for the high energy tandem (GaAs(1.43 eV)-Ga1−xAlxAs(1.94 ev)) of a four-band-gap photovoltaic converter combining two monolithic stacked cells coupled through a dichroic mirror, taking into account Joule heating, band-to-band absorption and free-carrier absorption in the 1.94 - 1.43 eV range (the dichroic mirror splits the spectrum at 1.43 eV) for the various IOC structures previously proposed and for the Ga0.15Al0.85As heavily doped junction. The Ga0.15Al0.85As IOC appears to be one of the best structures experimentally tested so far with an overall relative efficiency loss of 0.11η for η ≈ 30%.