I had a solar charger for backpacking that was somewhat highly rated. The charging rate was slow. It broke after a little more than a year of service. I think I had used it about 30 days.
I have switched to carrying a rechargeable battery with USB ports. I've gotten 12 days out of one. I will carry a second smaller one also. Occasionally both together if I have cell phone service where I am backpacking and I want to watch San Francisco Giants baseball while I am cooking and eating dinner.
I know there are very reliable solar chargers for the field. The question is, how much power do you need? I bet you could go two weeks with batteries that weigh very similar to whatever solar charging and battery system you would carry. After all, you need to carry a battery with your solar charger anyway.
For short, 2 to 3 days long, I prefer to use a power bank and leave solar panels behind. On a two week field project a few years ago, I did take a panel and it worked quite well. Usually the most important item to keep charged is my phone and that is fairly easy to accomplish with a relatively small power bank. Headlamps are #2 priority
depends on your need. For car camping I just charge while driving, In the field I put my phone on airplane mode and bring one backup. that seems to be enough for me. If you are charging all the time they work ok.
Since lightweight battery banks have become a thing the case for solar panels on trail for backpacking has diminshed. Generally they only work well in areas where it is sunny most days (eg the South West US) and even then unless you have a large array, can only charge things fairly slowly. You can (or could) find small fairly inexpensive fairly light (2-3 oz) arrays that will provide enough power to keep a small (3500 mAH) battery bank replenished if there is sun. Such a device may be worth carrying as backup if you like playing with such things. For most they just don't work well enough to be bothered with.
One thing that I have really enjoyed having on longer excursions in the backcountry is a Luci Solar Lantern and Charger. To charge it, I strap it to my pack while walking or place it away from shade at base camp. It produces a strong light at night, as well as being able to charge my phone in a pinch.
I've seen power banks with a solar panel built-in on one side. I think that would only be good for a topping-off trickle charge instead of a full charge mode. When my existing power bank wears out, I'll probably look into getting one of those kind.
Thank you all for the help. We are leaning towards a power bank, but not sure if that will be enough for 27 days and two phones. Also thanks for the advise on airplane mode, an REI salesperson also recommended that and we would have never thought of it .