[comicjk]

There are a lot of factors you're not considering. Reducing heat output is good, yes, but putting a layer between your chips and their heat sink is bad! Even though the total heat output is lower, the chip temperature will be higher, because it will be more insulated. There is no way around this; any heat-to-power device acts as insulation compared to a plain heat conductor. You will also have added weight and cost. In a phone, where the heat differences are small, the electricity gained will be almost nothing. So actually we're not likely to see this in phones.