Combinatorics

Physics

Electron

Mathematics

Diffusion

Crystallography

Gene

Semiconductor

Non-radiative recombination

Perovskite (structure)

Recombination

Voltage

Atomic physics

Nuclear physics

Chemistry

Materials science

Condensed matter physics

Semiconductor materials

Fermi level

Quantum mechanics

Optoelectronics

Biochemistry

Open-circuit voltage

Thermodynamics

Saturation (graph theory)

Advanced Energy Materials

Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage ( V OC ) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the V OC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the V OC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the V OC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐ V OC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the V OC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the V OC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS ‐V OC relation is of great importance.

On the Relation between the Open‐Circuit Voltage and Quasi‐Fermi Level Splitting in Efficient Perovskite Solar Cells