Open source I don’t know however I do know you can get “broken”, misshapen and loose solar cells on ebay and other such vendors pretty cheap and with a little sodering and some repurposed glass you can turn them into solar panels. Not the best but it’s a workaround.
Although for serious applications I’d say a standard solar panel would be best. You want your AP to last and stay powered. Also look into hooking it to different kinds of power sources besides solar. You also might want to investigate the open ecology project. It does make a fair bit of open hardware (not for this field per se but it does). You might be interested in their power cube or wind turbine, or steam engine or biomas engine though not all power generation options would be practical for a router (but might be practical for a decentralized power grid or safecoin mine of some sort).