I think we're far ways from solar tech being used in conventional means beyond watches and calculators and that's because as solar tech improves in efficiency; the power requirements also rise such that things like eink requires undisturbed, stable power of about 100 mW all across the substrate. Otherwise you will see discoloration. Watches and calculators work because their power draw has been fixed for decades, well into the uA or nA range while being able to sustain transient loads over long periods of time such that your circuit design can be coarse, but still effective in accomplishing its primary function.

Things like a wireless keyboard almost work because they share similar function to that of clocks in power requirements, but they still have a battery for minimum operation conditions otherwise you risk latency issues with the transceivers and even risk the wrath of the FCC denying certification. All solar gadgets operate on this principle which is the true limiting factor in solar design which is the need a redundant power source. You might as well should have spare AA batteries nearby. That is the true issue with solar tech moving forward because from an engineering perspective, it's quicker, easier, cheaper to just have an instant power source nearby that can be made on the cheap. The sun's intensity differs around the world, meaning you have to design the solar equipment; taking into that account, which further limits your design's possibilities. At that point, it's just not worth using Photovoltaic(PV) components when the efficiency is at best 20% and optimal conditions and below that everywhere else. Then there's the fact that AA batteries are easily made, easily disposable, and easily usable. After all, it's just salt, magnesium, and other common minerals of Earth's design.

TL:DR - It's just easier, cheaper to use AA batteries.