Effect of substrate effcut angle on AlGaInP and GaInP solar cells grown by molecular beam epitaxy

Abstract

We have studied characteristics of ~2.0 eV AlGaInP and ~1.9 eV GaInP solar cells on misoriented GaAs substrates grown by molecular beam epitaxy (MBE). Lattice-matched AlGaInP solar cells are of interest for space and concentrator photovoltaics, but there have been relatively few reports on such cells grown by MBE. Open circuit voltages for GaInP cells ranged from 1.29-1.30 V, while AlGaInP cells ranged from 1.35-1.37 V. The bandgap-voltage offset (W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> ) of GaInP cells decreased from ~575 mV to ~565 mV as misorientation angle increased from 0° to 10°, while W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> for AlGaInP cells remained nearly constant at 620 mV. Internal quantum efficiency (IQE) measurements show that current collection for AlGaInP cells is lower than in GaInP and indicates the need for a thinner emitter with good surface passivation; no trend in IQE was observed as a function of offcut. Although W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</sub> for AlGaInP was slightly higher than in GaInP, we believe that further optimization will allow MBE-grown AlGaInP to be a promising candidate for future top cell applications.