Have you used one? Are they worth it? What is the best charger considering the price, weight and size?
Why do you want a solar phone charger versus a traditional external battery? I own both and have only used my solar phone charger while backpacking. For that activity, there is no question that the $12 I spent on mine ([here’s the Ebay link if you want one](http://www.ebay.com/itm/12000mAh-Portable-Waterproof-Solar-Charger-Dual-USB-External-Battery-Power-Bank-/311429159162?var=&hash=item48829fd8fa:m:m4GR0Fldvv-UkKormGScC-A)) was worth it, but if you’re not planning on spending multiple days in areas without electricity, I would strongly advise just using a regular USB external battery pack.
It’s for backpacking.
These work: http://www.unitetolight.org/utl-c.html
And you can donate some to 3rd world countries as part of your purchase.
Of course, they don’t work too well if it’s cloudy.
Are you planning on burning things to cook food? You might want to get one of these:
http://www.amazon.com/BioLite-BL-CSA-Wood-Burning-Campstove/dp/B00BQHET9O
BB, 
I’d stick to solar power.
Ynotgo. That’s nice and small but the output is only 6W! Not sure if it’s up to charging cellphones.
Have you seen the [Outdoor Gear Lab’s solar charger comparison?](The 4 Best Portable Solar Chargers of 2023 | Tested by GearLab) I’ve used products they’ve recommended before and was thoroughly impressed.
^Great link. Thank you.