The best solar panels are getting at or above the efficiency of converting nuclear heat to electricity (about 1/3) so they probably shouldn’t get that poor efficiency label.
Some cells are getting 47%, which is ridiculous for a generator! The theoretical maximum efficiency for solar cell from the sun as it appears in the sky is about 68%, so that's pretty good!
However, how expensive is that cell going to be? How much maintenance does it need, and how fragile is the system once deployed? It's very obvious that PV efficiency has beed skyrocketing recently, and I don't thinks it's stopping soon, but a commercial PV panel available today is just breaking 20% efficiency. Luckily, sunshine is quite abundant.
Don't skip the betavoltaic battery, (or the brand-name: Betacel), which turns beta-radiation directly into electricity. They used them in the 70s to power pacemakers, since batteries were kinda shit back then, and implanting Prometium into people is just too epic not to do.
Nowadays we have tritium-decay betavoltaic batteries, on satellites, buried or underwater sensors and probably some too secret military stuff.
There's also radioisotope piezoelectric generators, where the electrons are caught by a cantilever and then released in regular pulses. An electron waterwheel if you will.
There's also fuel cells, where fuel is not burned to create steam to move something, but combined with oxygen in a different way (the end products still being the same) so the electrons shuttled around during this reaction can be utilised as electricity.
Think of combustion as oxidation of your fuel, the oxidation meaning that you (among other things) move electrons from the fuel to oxygen. In combustion, unfortunately you can't access the electrons directly, as they are always stuck in the chemical bonds of the molecules, that's why we take the detour via heat/mechanical - the steam engine. The fuel cell now separates fuel and oxygen, and thus divides the combustion reaction into two parts that happen at opposite sides of the cell. Those sides are divided by a membrane that does not allow the electrons to transfer across, so they need to take a detour through an electric circuit, in which we can harvest them as electrical power.
I always found it really fascinating that fuel cells are the only other technology than solar where the electrons we use as electrical power are more or less directly generated as opposed to the detour via a generator. Unfortunately, fuel cells are still a very niche technique.