Unfortunately there's only 1 good solution, another pan (new or used if you can locate one). They're not cheap new.
To replace it, the engine must be supported and the subframe lowered. I'd also get new oil pan-to-block o-rings (2) and an oil sump o-ring too. Volvo uses a liquid gasket and I wouldn't try using anything else.

Considering what will happen if the damaged pan crack gets worse, I wouldn't even attempt anything like JB weld or epoxy. That won't work because for one, oil will continually seep while you're trying to fix it. I've tryed that before to slow one that was waiting for a new pan, trying to keep it from making a mess losing oil but it didn't work.