Increasing the efficiency of triple-junction solar cells due to the metamorphic InGaAs subcell

The efficiency of GaInP/GaAs/In$_{x}$Ga$_{1-x}$As triple-junction solar cells obtained by replacing (in the widely used “classical” GaInP/GaAs/Ge heterostructure) the lower germanium with In$_{x}$Ga$_{1-x}$As subcell formed using the metamorphic growth technology has been investigated. Based on an original approach, the optimal indium concentration in the narrow-gap subcell has been found. The main parameters of In$_{x}$Ga$_{1-x}$As subcells with an indium concentration from $x$ = 0.11 to 0.36 were determined and were used to calculate the IV characteristics of GaInP/GaAs/In$_{x}$Ga$_{1-x}$As solar cells. It has been determined that at $x$ = 0.28 the efficiency of the triple-junction solar cell increases by 3.4% (abs) in comparison with the “classical” solar cell, reaching a value of 40.3% (AM1.5D). Also it has been shown that the efficiency of such solar cells can be increased up to 41%.