Ok, so gamma radiation is high energy light. Why can’t we power things with it like we can solar power?
Because it is so very high energy. Sit under the sun for ten minutes. You probably won’t be too badly damaged. If you sit in front of a gamma source for ten minutes, you have much greater risk of injury.
There may also be technical issues involved with “stepping down” gamma to electricity. Finally, the sun is free. Purifying gamma-emitting elements is expensive.
To go from light to electricity, the light (photons) need to interact with a material. To end up with a photocurrent (ie - electicity flowing as a result of shining a light on the material), the photons need to interact with electrons in the material. The photons in the visible region are of the appropriate energy (by and large coming from electron de-excitation emissions in the first place). Gamma range photons are of higher energy (generally originating from nuclear de-excitations) and thus don’t interact with the electrons within the material. Without interacting with the electrons, a photocurrent can’t be generated.