Voltage Deficit in Wide Bandgap Perovskite Solar Cells: The Role of Traps, Band Energies, and Effective Density of States

Wide-bandgap (greater than or similar to 1.7 eV) perovskite solar cells (PSCs) are plagued by relatively low open-circuit voltages. This is problematic as they are key to achieving perovskite silicon tandems, which can boost the potential of silicon solar cells. Performance in PSCs is widely considered to be limited by recombination at the interface between the perovskite and the transport layer (TL). Here, a number of design rules to increase the open-circuit voltage of wide-bandgap PSCs are introduced. A numerical device model that includes a detailed description of the interfacial recombination processes is presented. The combined effects of interface traps, ions, band alignment, and transport properties are introduced to identify the critical parameters for improving the open-circuit voltage. A large number of devices are simulated by picking random combinations of parameters and are looked for trends. It is shown that interface recombination can be suppressed by reducing the minority carrier density close to the interface with the TLs. It is demonstrated that the alignment of energy levels is only part of the story; the effective densities of states are of equal importance. The results pave the way to achieving high open-circuit voltages, despite a significant density of interface defects.