Minimum Effect of Non-Infinitesmal Intermediate Band Width on the Detailed Balance Efficiency of an Intermediate Band Solar Cell

This paper analyses the minimum deterioration of an intermediate band (IB) solar cell´s conversion efficiency as a function of the IB´s width. A central task in accomplishing this is to derive the emission spectrum of an IB material. The derivation is premised upon equilibria conditions and is derived under the stringent conditions that electronic transitions are limited to inter-band transitions coupled to photon emission or absorption. The resultant equilibrium emission spectrum is utilized to formulate expressions for the net photon flux and net power density absorbed by the IB material from a dual source solar geometry. Heuristic arguments are contrived to explain the relationship of the absorption coefficients and the absorptivity upon the conversion efficiency. Results indicate as the IB width increases, the conversion efficiency reduces to the limiting efficiency of a two-junction series-assembled tandem