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.
Shitty efficiencies[1] haven't stopped us from using combustion engines in cars for a century. But while combustion engines use expensive fuel, these solar cells use sunlight, which is free. So which technology should we celebrate?
[1]: 20% is already quite a good efficiency for a car in mixed traffic. That doesn't even account for all the energy used to provide the fuel.
So a panel that looks like Vanta Black, but also at non-optical wavelengths? Better efficiency is being pursued but the engineering behind real products will always be the result of balancing design constraints:
