Looks like the first Soviet satellite with solar power capability was Sputnik 3, launched on the 15th May 1958, losing out to Vanguard 1 which was the first satellite with solar power launched only two months earlier.
Of Sputnik 3, Wikipedia says
It was powered by silver-zinc batteries and silicon solar cells which operated for approximately 6 weeks
Sputnik 1 was filled with nitrogen to detect damages by micrometeroites causing a leak and a pressure loss. Therefore electrical vacuum feedthroughs were needed to connect the antennas to the transmitters.
Sputnik’s antennas consisted of four whips attached to the aluminum
enclosure through insulators that were spaced symmetrically around the