Both transient and steady state photoluminescence PL have been frequently used to analyze the properties of halide perovskite films1-2 and recently also layer stacks, i.e. films with inter-faces.3-5 Here, we present our current level of understanding of how to analyze the data. In the case of films, long decays in transient PL correlate well with strong steady state PL. The shape of the decays allows us to determine bimolecular and monomolecular recombination coeffi-cients.1, 6 In the case of films with one interface, we show that high luminescence is still bene-ficial for high open-circuit voltages in devices and still correlates with long photoluminescence decays.3 We show by simulation how the combination of steady state PL with tr-PL can be used to better understand band alignment at interfaces and how it provides an estimate of the surface recombination velocities. Finally, we discuss the case of layer stacks with two contacts and of full devices.7 Here, additional effects such as the conductivity and capacitance of con-tact layers become important. In addition, the question arises on how to compare purely opti-cal techniques with techniques that use electrical detection. One example is the comparison between transient PL and transient photovoltage. The difference between the two is that tran-sient PL measures the internal voltage, i.e. the quasi-Fermi level splitting, and transient photo-voltage measures the external voltage that builds up at the external terminals of the cell. While both decays are affected by the contact layers, the impact is substantially different. The exter-nal voltage first has to be built up by charging up the capacitance of the interfacial layers, the internal voltage peaks immediately after the laser pulse and then decays fairly quickly.

Recombination and the concept of charge carrier lifetimes in lead-halide perovskites

ACS Fall 2021

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