Charge-Carrier Dynamics, Mobilities and Diffusion Lengths of 2D-3D Lead Halide Perovskites
Leonardo Buizza a, Zhiping Wang a, Timothy Crothers a, Rebecca Milot a, Henry Snaith a, Michael Johnston a, Laura Herz a
a University of Oxford, Department of Physics, Clarendon Laboratory, UK, Parks Road, United Kingdom
International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2020 May 12th - 14th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Leonardo Buizza, 056
Publication date: 6th February 2020

Perovskite solar cells have improved drastically over the past decade, overcoming hurdles of temperature- and water-induced instability to achieve efficient, stable devices. Three-dimensional (3D) perovskites have excellent properties including high charge-carrier lifetimes and mobilities, strong absorption and good crystallinity – ideal for photovoltaic devices. However, 3D perovskite materials struggle especially with moisture-induced degradation [1]. The addition of large, hydrophobic organic cations can lead to the formation of two-dimensional (2D) perovskite structures. Devices made with 2D perovskites show much greater stability, but with far lower power conversion efficiencies than their 3D cousins [2]. Materials combining 2D and 3D structures have thus recently become one the most promising candidates for use in solar cells [3, 4]. In order to fully understand the optoelectronic properties of these 2D-3D hybrid systems we look at BAx(FA0.83Cs0.17)1-xPb(I0.6Br0.4)3 across the composition range 0 ≤ x ≤ 80 %. We find that small amounts of butylammonium (BA) help to improve crystallinity and passivate grain boundaries, thus reducing monomolecular charge-carrier recombination, and boost charge-carrier mobilities. Excessive amounts of BA lead to poor crystallinity and inhomogeneous films forming, greatly reducing charge-carrier transport capabilities. For low amounts of BA the benevolent effects of reduced recombination and enhanced mobilities lead to outstanding diffusion lengths.

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