The Important Role of Optical Absorption in Determining the Efficiency of Intermediate Band Solar Cells and a Design Principle for Perovskite Doping.

The efficiency of solar cells can be increased by introducing an intermediate band (IB) in the band gap. Considering that absorption within the band gap is typically weak, the efficiency of IB solar cells was overestimated previously, with a strong enough optical absorption assumed. Here, we propose a new formulism to calculate the limit of the efficiency of IB solar cells with the ideal absorption assumption removed, which can be used to evaluate the effect of absorption. New IB materials are designed via doping double perovskite, which has a relatively strong absorption within the band gap with both d-p and s-p transitions. The limit of the efficiency of a 2 μm thick Sn-doped Cs 2 AgBiBr 6 is 38.6% under the AM1.5G spectrum, which is only ∼6% smaller than the ideal-absorption estimation. Results presented here provide a new dimension in the rational design of IB solar cell materials.