Influences of bulk and surface recombinations on the power conversion efficiency of perovskite solar cells

For a novel kind of solar cell (SC) material, it is critical to estimate how far the power conversion efficiencies (PCEs) of the SCs made of it can go. In 2010 Han and Chen proposed the equation for the ultimate efficiency of SCs without considering the carrier recombination eta(un). eta(un) is capable of estimating the theoretical upper limits of the SC efficiencies and has attracted much attention. However, carrier recombination, which is one of the key factors influencing the PCEs of the SCs, is ignored in the equation for eta(un). In this paper, we develop a novel equation to calculate the ultimate efficiency for the SCs, eta(ur), which considers both the bulk and the surface carrier recombinations. The novel equation for eta(ur) can estimate how much the bulk and the surface carrier recombinations influence the PCEs of the SCs. Moreover, with eta(ur) we can estimate how much PCE improvement space can be gained only by reducing the influence of the carrier recombination to the least. The perovskite organometal trihalide SCs have attracted tremendous attention lately. For the planar CH3NH3PbI3 SCs, in the material depth range from 31.25-2000 nm, we apply the equation of eta(ur) to investigate how the bulk and the surface carrier recombinations affect PCE. From a typically reported PCE of 15% for the planar CH3NH3PbI3 SC, using the equation of eta(ur), it is concluded that by reducing the influence of carrier recombination to the least the improvement of PCE is in the range of 17-30%.