A comparative study on photon recycling effects in n+-p and p+-n InP solar cells with Bragg reflector

Numerical calculation of photon recycling(PR) effect has been carried out for n(+)-p and p(+)-n structure InP cells with Bragg reflector(BR). For both structures with a thin (less than or similar to 0.1 mu m) emitter, PR effects on photocurrent are scarcely observed. A large contribution of PR to photocurrent is found for an n(+)-p structure with a thick (greater than or similar to 0.5 mu m) emitter although photocurrent itself is reduced. A p(+)-n structure with a similar configuration, on the other hand, shows very small PR effects. Such a difference in the magnitude of PR effects between both cell structures is brought by the difference in radiative and nonradiative lifetimes between n(+) and p(+) emitters. An increase in Voc is found for an n(+)-p cell with a thin (similar to 2 mu m) base layer. As results of increases in photocurrent and Voc by PR, conversion efficiency of a n(+)-p cell is increased by about 3%. For both cell structures, BR effects are observed for a base thickness less than about 3 mu m. The effects are not due to the trapping of reemitted light but the trapping of incident light.