There are a bunch of physical reasons why you can't have a ~100% efficient solar cell – obviously thermodynamics chief among them, but also effects like the fac

There are a bunch of physical reasons why you can't have a ~100% efficient solar cell – obviously thermodynamics chief among them, but also effects like the fact that the bandgap is finite (yet the sun's black-body spectrum has energy radiated below it) and the fact that solar cells themselves will heat up and re-radiate photons they absorb. For a long time, solar cell efficiency was around ~10-20%. There's actually a theoretical upper limit, the Shockley–Queisser limit, of a bit less than 34% for a single p-n junction photocell. [1] This is a tandem cell – for which higher efficiencies are possible but costs go up. The thermodynamic limit is reached if you have an infinite number of layers. Obligatory plot of progress vs time: https://upload.wikimedia.org/wikipedia/commons/2/25/Best-research-cell-efficiencies-rev220126_pages-to-jpg-0001.jpg https://upload.wikimedia.org/wikipedia/commons/2/25/Best-res... [1] https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limit https://en.wikipedia.org/wiki/Shockley%E2%80%93Queisser_limi...