Development of 20% efficient GaInAsP solar cells

The authors report on the development of two compositions of a GaInAsP lattice-matched to GaAs for photovoltaic applications. Successful development of cascade solar cells necessitates the development of both high bandgap (1.5 to 1.9 eV) as well as low bandgap (0.7 to 1.4 eV) materials. The GaInAsP lattice-matched to GaAs is an excellent candidate for the high band gap material. Ga_0.84In _0.16As_0.68P_0.32 cells, with a band gap of 1.55 eV, have been developed that have demonstrated a V_oc of 1.047 volts, a J_sc of 22.5 mA/cm², a fill factor of 0.849, and an active area efficiency of 21.8 per cent under AM1.5 direct illumination. A Ga_0.84In_0.16As_0.68P_0.32 tunnel diode has also been developed with a peak current of 4.33×102~mA/cm² at a voltage of 65 mV. Both the Ga_0.84In_0.16As_0.68P_0.32 cell and tunnel diode are being used in conjunction with a Ge cell to develop a monolithic Ga_0.84In_0.16As_0.68P_0.32/Ge cascade cell. Ga_0.68In_0.32As_0.34P_0.66 cells, with a band gap of 1.7 eV, have been developed that have demonstrated a V_oc of 1.161 volts, a J_sc of 28.9 mA/cm2 a fill factor of 0.86, and an active area efficiency of 21.4 per cent under AMO illumination. The Ga_0.68In_0.32As _0.34P_0.66 cells have also demonstrated resistance to radiation damage as well as a recovery of preirradiation performance after low temperature annealing