Understanding recombination processes in perovskite solar cells using frequency and time domain measurements
Adam Pockett a, Matthew Carnie a
a SPECIFIC, Swansea University, Baglan Bay Innovation and Knowledge Centre, Baglan, SA12 7AX, United Kingdom
Proceedings of International Conference on Impedance Spectroscopy and Related Techniques in Metal Halide Perovskites (PERIMPED)
Online, Spain, 2020 October 6th - 7th
Organizers: Juan Bisquert, Bruno Ehrler and Eline Hutter
Invited Speaker, Adam Pockett, presentation 015
Publication date: 25th September 2020

The existence of slow dynamic processes in perovskite solar cells is well-known. This is most commonly observed as hysteresis in the current-voltage curve during device efficiency measurements. Slow processes have also been observed in a range of frequency and time domain measurements. Whilst there is considerable evidence linking the origins of these observed processes to the migration of ions within the perovskite, the exact nature of their interaction with the electronic structure of the device is still unclear.

We have employed a range of complimentary frequency and time domain characterization techniques in an attempt to understand these complex interactions. These techniques include impedance (EIS), intensity modulated photovoltage/photocurrent (IMVS/IMPS) and transient photovoltage/photocurrent spectroscopies (TPV/TPC). We have also studied a range of cell architectures from planar to triple-mesoporous perovskite devices. Unusual behaviours such as the negative transient photovoltage/photocurrent response appear to have analogous behaviours in the frequency domain in the form of multiple arcs and loops. It is our hope that by combining the use of both of these techniques it may help our interpretation of device operation.

For example, our previous findings from temperature dependent EIS measurements allowed us to establish a clear link between ionic redistribution and changing recombination rates. This process has also been identified in TPV measurements during the slow Voc rise under illumination. We employed this understanding to measurements performed on triple-mesoporous perovskite devices containing the additive 5-AVAI, which revealed the inhibition of ionic movement due to the presence of the additive. This property is related to the exceptionally slow response time of these devices, and also their improved stability.

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