  Perovskite semiconductors have demonstrated outstanding external luminescence
quantum yields, enabling high power conversion efficiencies (PCE). However, the
precise conditions to advance to an efficiency regime above monocrystalline
silicon cells are not well understood. Here, we establish a simulation model
that well describes efficient p-i-n type perovskite solar cells and a range of
different experiments. We then study important device and material parameters
and we find that an efficiency regime of 30% can be unlocked by optimizing the
built-in potential across the perovskite layer by using either highly doped
(10^19 cm-3), thick transport layers (TLs) or ultrathin undoped TLs, e.g.
self-assembled monolayers. Importantly, we only consider parameters that have
been already demonstrated in recent literature, that is a bulk lifetime of 10
us, interfacial recombination velocities of 10 cm/s, a perovskite bandgap of
1.5 eV and an EQE of 95%. A maximum efficiency of 31% is predicted for a
bandgap of 1.4 eV. Finally, we demonstrate that the relatively high mobile ion
density does not represent a significant barrier to reach this efficiency
regime. Thus, the results of this paper promise continuous PCE improvements
until perovskites may become the most efficient single-junction solar cell
technology in the near future.
