Relating Sub-Bandgap Electronic Defects and Open-Circuit Voltage in Perovskite Solar Cells
Guus Aalbers a, Tom van der Pol a, Kunal Datta a, Willemijn Remmerswaal a, Martijn Wienk a, René Janssen a b
a Molecular Materials and Nanosystems, Institute for Complex Molecular Systems, Eindhoven University of Technology, The Netherlands
b Dutch Institute for Fundamental Energy Research, Eindhoven, The Netherlands
Proceedings of Device Physics Characterization and Interpretation in Perovskite and Organic Materials (DEPERO)
VALÈNCIA, Spain, 2023 October 3rd - 5th
Organizers: Sandheep Ravishankar, Juan Bisquert and Evelyne Knapp
Oral, Guus Aalbers, presentation 002
Publication date: 14th September 2023

The efficiency of perovskite solar cells is negatively affected by open-circuit voltage losses due to radiative and non-radiative recombination of charges. The exact origin of these voltage losses and the individual contributions of radiative and non-radiative processes are not known. Presently, radiative voltage limits, determined from sensitive photocurrent measurements covering the above- and sub-bandgap regions, often yield unphysically low values. Herein, sensitive photocurrent and electroluminescence spectroscopy are used to probe radiative recombination at sub-bandgap defects in wide-bandgap mixed-halide lead perovskite solar cells. The radiative ideality factor associated with the optical transitions increases from 1, above and near the bandgap edge, to ~2 at mid-bandgap. Such photon energy-dependent ideality factor corresponds to a many-diode model. The radiative open-circuit voltage limit derived from this many-diode model enables the differentiation of radiative and non-radiative voltage losses in perovskite solar cells. The latter are further deconvoluted into contributions from the bulk and interfaces via determining the quasi-Fermi level splitting. The experiments show that while sub-bandgap defects do not contribute to radiative voltage loss, they do affect non-radiative voltage losses.

The authors are grateful for fruitful discussions with Thomas Kirchartz (Forschungszentrum Jülich, Germany) regarding the radiative ideality factor. We acknowledge funding from the Netherlands Ministry of Education, Culture, and Science (Gravity program 024.001.035) and the Netherlands Organization for Scientific Research (NWO) for funding through the Joint Solar Programme III (project 680.91.011) and the Spinoza prize.

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