How Charge Dynamics Change in Mixed Halide Perovskites on Light Soaking
Dengyang Guo a, Zahra Garmaroudi b, Samuel Stranks b, Tom Savenije a
a Delft University of Technology, The Netherlands, Julianalaan, 136, Delft, Netherlands
b Cavendish Laboratory, University of Cambridge - UK, JJ Thomson Avenue, 9, Cambridge, United Kingdom
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics, Photonics and Optoelectronics (ABXPV18PEROPTO)
Perovskite Thin Film Photovoltaics (ABXPV18). 27-28 Feb
Rennes, France, 2018 February 27th - March 1st
Organizer: Jacky Even
Oral, Dengyang Guo, presentation 062
DOI: https://doi.org/10.29363/nanoge.abxpvperopto.2018.062
Publication date: 11th December 2017

The highest efficiency of solar cells based on metal halide perovskites as light absorber has reached 22.1%. Interestingly, the used perovskite comprise a mixture of cations (MA+, FA+, and Cs+ ) and halides (I-, Br-). Despite the excellent performance, these perovskites exhibit some phase segregation on light soaking as demonstrated by photoluminescence and XRD. However, it is unclear how the segregation affects the dynamics of charge carriers. In this work we carried out time-resolved microwave-conductivity (TRMC) measurements to investigate the dynamics of mobile charge carriers before and after light soaking using a similar light intensity as AM1.5. We have studied thin spin-coated layers on quartz of (FA0.79MA0.16Cs0.05) Pb (I1-xBrx)3 with x ranging from 0 to 1. For x < 0.5 we find that on light soaking in nitrogen environment the charge carrier lifetime increases, while for x > 0.5 the lifetime is reduced. The charge carrier mobilities of the mixed perovskites reduce gradually from 36 cm2/Vs for x = 0 to 16 cm2/Vs for x = 1. Interestingly, these values are not affected by light soaking, which implies that the major part of the perovskite is not influenced by light soaking, whereas the decay pathways have changed. By analysing the TRMC traces with a mathematical model, we propose that for x< 0.5 light soaking leads to a reduction of the number of shallow states. Two months after light soaking, samples with x < 0.5 are only partially recovered including the shallow states, while samples with x > 0.5 are fully recovered. In summary, the above results provide guidelines for which I/Br ratio we can expect the best performance and stability.

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