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Combination of transient and steady-state photoluminescence for the characterization of halide perovskite-based layer stacks

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Both transient and steady state photoluminescence PL have been frequently used to analyze the properties of halide perovskite films1 and recently also layer stacks, i.e. films with interfaces.[2-4] 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 coefficients, the former of which is clearly affected by photon recycling.[1, 5] In the case of films with one interface, we show that high luminescence is still beneficial for high open-circuit voltages in devices and still correlates with long photoluminescence decays.[2] 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. Here, additional effects such as the conductivity and capacitance of contact layers become important. In addition, the question arises on how to compare purely optical techniques with techniques that use electrical detection. One example is the comparison between transient PL and and transient photovoltage. The difference between the two is that transient PL measures the internal voltage, i.e. the quasi-Fermi level splitting, and transient photovoltage 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 external 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.

This talk is part of the Optoelectronics Group series.

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