86.8% is for an infinite number of layers with concentrated solar. 33.7% is the max for a single layer p-n junction, which is what most readily available cells

86.8% is for an infinite number of layers with concentrated solar. 33.7% is the max for a single layer p-n junction, which is what most readily available cells are. The most expensive, high efficiency cells, like those on spacecraft, are 3 layer. They are too expensive to be practical on Earth.