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 (≲ 0.1 μm) 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 (≳0.5 μm) 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 (~2 μm) 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, PR effects are observed for a base thickness less than about 3 μm. The effects are not due to the trapping of re-emitted light but the trapping of incident light