Lawrence Berkeley National Laboratory

Conversion of solar radiation to electricity with photon-enhanced thermionic emission (PETE) holds the theoretical promise of high conversion efficiency. Basic questions of converter materials properties and conversion process thermodynamics were addressed in recent work. Here we investigate two configurations of front and back electrical contacts on a silicon cathode, and the dependence of device efficiency on the contact area, using a two-dimensional detailed simulation. The impact of contact area on efficiency is different at moderate vs. high temperature, due to a change from electron recombination to electron injection at the contact. When the contact is small enough, a local potential gradient develops, which forms an effective barrier against electron recombination. The back contacts lead to higher efficiency compared to front contacts at all temperatures, and allow much higher contact area that may serve to reduce Ohmic loss and to absorb IR radiation.