I finally find where is the diode using in solar charger in step Step 8: Wire Up The Charge Controller
, and from the explaination that "One of the reasons I like using this little charge controller is that its hard to screw up. There are 4 solder points on it. In the front next to the mini-USB port are where we hook up the DC power, which in our case in solar, and the two spots in the rear are for the battery.", we can know it is very likely for reverse polarity protection. Then it's the same function as D3 ss14 on our pcb. So you don't have to use another diode if you purchased our one.