Efficiency is about getting more out of the sand amount of surface. If double the surface gives the same amount of electricity, but is 10 times cheaper, the cost per kWh drops by a factor of five.

The cost of solar has come down, because it’s price follow an observed law where a doubling in installed capacity drops the price by 20% (Swanson’s law)

Efficiency is part of that equation, but the efficiency hasn’t gone up that much. It’s mostly production capacity that accounts for the savings.