Solar energy is a ways off. It's used on conventional quartz watches, but they draw a minuscule amount of power, and they don't have to put a full-color display where the solar panels go.
Battery chemistry can be called "technology", I suppose. Lithium-ion batteries are always being repackaged to fit different spaces, but I think their chemistry itself is reaching its limits.
System CPUs and software can also be made to manage power consumption more efficiently. This is more about battery
life, not
capacity, but the end result is similar. The fewer clock cycles, the better; and more computation that can be done with each cycle means even less power draw. A big help for battery life in the iPhone 5S was the 64-bit system, needing less power to run the same tasks than the previous 32-bit architecture required.