Let me try to do the math here, please correct me if I'm wrong. The band gap of Si in solar cells is about 1.1 ev. To excite three electrons, a photon thus nee

Let me try to do the math here, please correct me if I'm wrong. The band gap of Si in solar cells is about 1.1 ev. To excite three electrons, a photon thus needs 3.3ev, or about 370nm. The visible spectrum starts around 380nm or 390nm, depending on which source you believe. So the triple photon frequency would be very near UV. According to this spectrum [0], there's a sharp drop in solar power around the 370nm. It seems that with the 1.1ev band gap, exciting three electrons doesn't seem to be worth it. But, if you could reduce it just a bit (by doping, most likely), it might be worth considering. Of course, reducing the band gap would likely lead to much worse performance overall, so one would need a multi layer approach, which sounds pretty complicated. And then you need to pray that your glass cover doesn't absorb the UV light, which seems to be a pretty close call[1]. [0]: https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spectrum_en.svg https://en.wikipedia.org/wiki/Sunlight#/media/File:Solar_spe... [1]: https://en.wikipedia.org/wiki/Soda%E2%80%93lime_glass#/media/File:Soda-lime_glass,_typical_transmission_spectrum_(2_mm_thickness).svg https://en.wikipedia.org/wiki/Soda%E2%80%93lime_glass#/media...