Asymmetric Charge Carrier Transfer and Transport in Planar Lead Halide Perovskite Solar Cells

Weidong Xu^a, Tian Du^a^,^b, Michael Sachs^a, Thomas J. Macdonald^a, Ganghong Ming^a, Lokeshwari Mohan^b, Chieh-Ting Lin^a^,^b, Jiaying Wu^a, Martyn A. McLachlan^b, James R. Durrant^a^,^c

^aDepartment of Chemistry and Centre for Processable Electronics, Imperial College London, London, W12 0BZ, United Kingdom

^bDepartment of Materials and Centre for Plastic Electronics, Imperial College London, London, W12 0BZ, United Kingdom

^cSPECIFIC IKC, College of Engineering, Swansea University, SA2 7AX, United Kingdom, United Kingdom

International Conference on Hybrid and Organic Photovoltaics
Proceedings of 13th Conference on Hybrid and Organic Photovoltaics (HOPV21)

Online, Spain, 2021 May 24th - 28th

Organizers: Marina Freitag, Feng Gao and Sam Stranks

Oral, Weidong Xu, presentation 051
Publication date: 11th May 2021

Metal halide perovskites have shown remarkable success in photovoltaic applications by hitting efficiencies over 25%.[1,2] Despite the enormous contributions from material and device engineering, understandings of device physics, which is critical to optimize the design of perovskite solar cells towards their theoretical limit, are still lacking and debating. One is the kinetics and coherence of charges transport within the perovskite layer and transfer from the perovskite to its interlayers.

Herein, we demonstrate a simple and time-resolved photoluminescence (TRPL) method to characterize charge transport across bulk perovskite and charge transfer from perovskite to the interlayers. An asymmetric charge carrier distribution between the charge transport layer (CTL) and methylammonium lead iodide (MAPbI₃) surface and its opposite side was created by using a much higher energy excitation light with a very short penetration depth of ~30 nm. As such, most charge carriers will be generated very locally at the selected surface, where charge transfer kinetics of TRPL will be more pronounced if the charges are generated at the CTL/MAPbI₃ interface, while charge diffusion processes will be more distinguished when generated at the opposite side. This is because, under the later condition, charges need to diffuse across the MAPbI₃ film before reaching the interface and to be transferred. We then conducted this TRPL measurement on three typical MAPbI₃ perovskites with two varying thicknesses of 250 nm and 750 nm, and another 750 nm perovskite with an additional post-treatment: aerosol assisted solvent (AAS) annealing for removing grain boundaries (GBs) in the vertical direction. Finally, a numerical calculation was conducted based on these TRPL kinetics to interpret charge transfer and diffusion parameters.

Our results elucidate the dependence of these kinetics on film thickness, GBs, and interlayers. Affected by film thickness and GBs, MAPI₃ shows an asymmetry between electron and hole in terms of charge transport across bulk MAPI₃ as well as charge transfer from MAPI₃ to the interlayers.

References:

[1] Yoo, J. J.; Seo, G.; Chua, M. R.; Park, T. G.; Lu, Y.; Rotermund, F.; Kim, Y.-K.; Moon, C. S.; Jeon, N. J.; Correa-Baena, J.-P.; Bulović, V.; Shin, S. S.; Bawendi, M. G.; Seo, J. Efficient Perovskite Solar Cells via Improved Carrier Management. Nature 2021, 590 (7847), 587–593

[2] Jeong, J.; Kim, M.; Seo, J.; Lu, H.; Ahlawat, P.; Mishra, A.; Yang, Y.; Hope, M. A.; Eickemeyer, F. T.; Kim, M.; Yoon, Y. J.; Choi, I. W.; Darwich, B. P.; Choi, S. J.; Jo, Y.; Lee, J. H.; Walker, B.; Zakeeruddin, S. M.; Emsley, L.; Rothlisberger, U.; Hagfeldt, A.; Kim, D. S.; Grätzel, M.; Kim, J. Y. Pseudo-Halide Anion Engineering for α-FAPbI3 Perovskite Solar Cells. Nature 2021.

Acknowledgements:

We would like to thank the financial support from SUNRISE project (EP/P032591/1), China Scholarship Council, and Application Targeted and Integrated Photovoltaics (ATIP) programme from EPSRC

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