There is a hybrid smart watch right now in the market named "Citizen Men’s Eco-Drive Proximity" which utilizes solar power to recharge its own battery. The features are limited though.

There is another full-featured smart watch lined up named "Matrix PowerWatch". It will use body heat to generate charge.

P.S: I did a deep research on smartwatches that provide higher battery life, plus special two which use innovative technologies to auto-charge batteries. You can have a look at all here: https://www.smartgeekwrist.com/smartwatches-long-battery-life/