PERC stands for Passivated Emitter and Rear Cell technology. The way that the PERC manufacturing process is different from standard panels is that an extra step is added of:
1. Application of a back surface passivation layer
2. Creating small pockets in the passivation layer using lasers or chemicals, to absorb more light
Of course, every manufacturer has their own details that they include in making each panel unique. For example Hanwha has its own modification on the PERC model called Q.ANTUM technology.
Martin A. Green, The Passivated Emitter and Rear Cell(PERC):From conception to mass production, Solar Energy Materials & Solar Cells 143 (2015) 190–197