Pathways towards 30% efficient perovskite solar cells

Perovskite semiconductors have demonstrated outstanding external luminescence quantum yields, therefore potentially allowing power conversion efficiencies (PCE) close to the thermodynamic limits. However, the precise conditions that are required to advance to an efficiency regime above monocrystalline silicon cells are not well understood. In this work, we establish a simulation model that well describes efficient p-i-n type perovskite solar cells (PCE~20%) and a range of different experiments helping to quantify the efficiency-limiting processes in state-of-the-art devices. Based on these results, we studied the role of important device and material parameters with a particular focus on chemical doping, carrier mobilities, energy level alignment and the built-in potential (V_BI) across all stack layers. We demonstrate 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 100 cm/s, a perovskite bandgap (E_gap) of 1.47 eV and an EQE of 95%. A maximum efficiency of 31% is obtained for a bandgap of 1.4 eV using doped TLs. 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.