Since this cell technology has reached an unprecedented level of efficiency, most concentrator photovoltaics systems are now being constructed using III-V multi-junction cells. The III-V multi-junction cell with triple junction modified GaInP/GaInAs/Ge structure is the first solar cell of any type to achieve an efficiency of more than 40% in 2006, and the independently confirmed efficiency is 40.7% (AM1.5D, low AOD, 240 suns, 25°C) [1], and the reverse metamorphic triple junction cell has reached 40.8% [2]. The rapid growth of cell efficiency in recent years [1-12] and its powerful leverage effect on reducing system costs have prompted people to re-examine the upper limit of cell efficiency. In this article, we will study "How high can cell efficiency be?" from both theoretical and experimental perspectives.
According to the sub-cell band gap, the power part of the ground solar spectrum used by each sub-cell in the 3-junction 1.9-eV GaInP/1.4-eV GaInAs/0.67-eV Ge is shown. The power of each subunit is tracked through the above-mentioned non-absorption, thermalization, and offset loss from the band edge to the Fermi level. Increasing the concentrator photovoltaics level to 500 suns in the figure is an effective way to reduce the loss from the band edge to the Fermi level. The right side of the figure shows two more favorable band gap combinations that can be used to divide the power density of the solar spectrum: a triple junction reverse metamorphic cell with a 1.9-eV GaInP/1.4-eV GaInAs/1.0-eV GaInAs structure, and AlGaInP/ GaInP/AlGaInAs/GaInAs/GaInNAs/Ge 6 junction ground concentrator photovoltaics unit. These basic efficiency losses, as well as losses due to series resistance and grid shadows, as well as ideal fill factor and sub-cell current matching, are plotted as a function of the indium content in sub-cell 2 of the vertically metamorphic triple-junction GaInP/GaInAs/Ge solar cell. With the increase in indium content and lattice mismatch, and the corresponding decrease in the band gap of the top two junctions, the relative importance of each mechanism.
Metamorphic solar cells with a triple junction GaInP/GaInAs/Ge structure are the first to achieve an efficiency of more than 40%, and the independently confirmed efficiency is 40.7% (AM1.5D, low AOD, 240 suns, 25°C). The high efficiency of the currently mass-produced III-V multi-junction cells, as well as the higher efficiency of next-generation cells, effectively utilize low-cost ground concentrator photovoltaics systems.