Failure analysis of thin‐film four‐junction inverted metamorphic solar cells

Abstract

AbstractInverted metamorphic solar cells play an important role in the field of photovoltaics, because it can directly grow stacked tandem junctions with different bandgaps according to the spectrum. We have found that the four‐junction AlGaInP/AlGaAs/InGaAs/InGaAs solar cells with the bandgap of 1.96/1.55/1.17/0.83 eV on the basis of the inverted metamorphic three‐junction AlGaInP/AlGaAs/InGaAs materials will cause a serious decrease in short‐circuit current density but with a normal open‐circuit voltage. The sharp decrease in short‐circuit current density is not attributed to the mismatched buffers dislocations penetrating into the active region of the InGaAs subcells but resulted from the minority carrier recombination due to defects in the AlGaInP subcell, which is observed directly from transmission electron microscopy, external quantum efficiency, electroluminescence, and secondary ion mass spectrometry measurements. The process of growing AlGaInP materials by metal–organic chemical vapor deposition easily introduces Al‐O deep‐level defects, resulting in the poor collection of minority carriers in AlGaInP materials. After improving the growth conditions of AlGaInP materials, a four‐junction solar cell with a photoelectric conversion efficiency of 34.9% and an open‐circuit voltage of 3.53 V was obtained.