 In September 2013, a four layer cell reached 44.7 percent efficiency.Numerical analysis shows that the "perfect" single-layer solar cell should have a bandgap of 1.13 eV, almost exactly that of silicon.Such a cell can have a maximum theoretical power conversion efficiency of 33.7% – the solar power below red (in the infrared) is lost, and the extra energy of the higher colors is also lost.