Effect of substrate off-orientation on the characteristics of GaInP/AlGaInP single heterojunction solar cells

The effects of GaAs substrate off-orientation on GaInP/AlGaInP heterojunction solar cells were investigated. The performances of solar cells fabricated on 2 degrees and 10 degrees off GaAs substrates were compared. The short circuit current densities were 10.44 mA/cm(2) for the 10 degrees off sample, 7.15 mA/cm(2) and 7.41 mA/cm(2) for the 2 degrees off samples, which showed 30% higher short-circuit current density for 10 degrees off samples. Also, 30% higher external quantum efficiencies and smooth surface morphology were observed in the solar cell fabricated on the 10 degrees off GaAs substrate. Secondary ion mass spectrometry depth profiles showed that the solar cells on 2 degrees off substrates had a 20-times higher oxygen concentration than the solar cells on 10 degrees off GaAs substrate in the n-GaAs/GaAs buffer layer. The 30% reduction for the solar cells on 2 degrees substrates in short circuit current density (J(sc)) was attributed to the higher oxygen concentration of the 2 degrees off samples than the 10 degrees off samples. I-V characteristics comparison between different front contact grid patterns was also performed for optimization of grid contacts. A 0.47 V bandgap-voltage offset, one of the device performance figures of merit to compare PV cells with different materials, was obtained.