Surface recombination is a form of efficiency loss in a solar cell.
In semiconductor crystals such as silicon, the atoms are usually bound to each other. However, on the surface of the material, there are no atoms to bond to on one side. This creates a “dangling bond”, and introduces states in the band gap much like the trap assisted recombination.
In silicon solar cells, this inefficiency can be avoided by “passivating” the surface. Passivating the surface is where you take silicon and react it with oxygen to create silicon-dioxide – this essentially removes the dangling bond. One has to be careful when passivating the surface as silicon-dioxide is an insulator. If you passivate the entire solar cell, then you will have a very difficult time pulling electrons out of the cell.