Mending broken solar cells
First the easy answer then the difficult one.


Easy answer buy very low cost cells from China. Less than $1 us including shipping to my house in the US. Here's a link
Tough Answer: To connect the pieces you need to..... find which of the electrodes are P and N junctions. This is not easy with pieces. If you can figure it out you need to connect all the wire traces of the P junctions and all the wire junctions of the N junctions. 
Here's a link to a picture of the back of a cell with positive and negative terminals.


Not sure this is clear, but it's very difficult after the cells are broken.