Recombination via Shallow Defects in Halide Perovskites and its Implications for the Concept of a Charge-Carrier Lifetime
Thomas Kirchartz a
a IEK5-Photovoltaik, Forschungszentrum Jülich
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
Invited Speaker, Thomas Kirchartz, presentation 017
Publication date: 14th September 2023

Recombination in semiconductors is often quantified using the concept of a charge-carrier lifetime. This is particularly sensible either in doped semiconductors or in intrinsic semiconductors with dominant recombination via deep defects. In both cases, the carrier density will decay exponentially after a pulsed excitation and assigning a characteristic time to this exponential decay is then a sound approach to analyze the data. However, in halide perovskites, intrinsic defects are predominantly shallow. Furthermore, in the popular lead-halide perovskites with a significant fraction of I as anion, the doping density is extremely low. Thus, the decay is not always exponential. We show that if care is taken to maximize the dynamic range of transient photoluminescence measurements, the decay is often highly non-exponential and in fact more resembling a power law of photoluminescence intensity being approximately proportional to 1/time². This has important consequences for the interpretation of the data. The concept of a lifetime becomes less helpful as the experimentally observed decay time is a strong function of carrier density and therefore laser fluence. Furthermore, repetition rate becomes very important as the decay time depends also on the time (approximately linearly) at which the decay time is determined. We discuss the alternative approach to introduce a recombination coefficient instead and explain how to relate this coefficient to the properties of the shallow traps.  

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