Publication date: 15th December 2025
Understanding the photocurrent in a solar cell is a matter of looking at the competition between charge carrier collection and recombination. In perovskite solar cells, these processes are affected by the redistribution of mobile ions during current-voltage scans and degradation, leading to the welk-known hysteresis, so-called ion-induced losses, and slow transients [1].
In this talk, spectrally resolved measurements together with device simulations are presented to better understand the loss mechanisms related to photocurrent. The approach exploits different penetration depths of the light due to the absorption coefficient of the perovskite varying with wavelength. Preconditioning samples under various conditions such as bias voltage and then "freezing" the ion distribution by cooling, allows for a measurement of the external quantum efficiency (EQE) under a stable ion distribution. Subsequent EQEs then monitor the effect of ion redistribution on the spectral shape of the EQE and thus depth-dependent charge collection probability [2].
This method is applied to Carbon-based mesoscopic solar cells with titania and zirconia scaffolds and to SAM-based pin solar cells. Together with the simulations, it provides explanations of certain shapes of the hysteresis such as inverted hysteresis or current overshoots ("bump") in the current-voltage curve [3]. The overall methodology might become a powerful tool to investigate underlying causes of device degradation upon ageing.
This research received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no. 851676 (ERC StGrt).
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