Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
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.