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Abstract title Charge recombination dynamics in FA0.85MA0.15PbI2.55Br0.45 perovskite thin films
Author Minda, Iulia, Stellenbosch University, Stellenbosch, South Africa (Presenting author)
Co-author(s) Horn, Jonas
Ahmed, Essraa
Schlettwein, Derck
Schwoerer, Heinrich
Abstract text

Perovskite materials were first introduced to the field of emerging photovoltaics (PVs) as photoabsorbers in traditional dye sensitised solar cells, however with poor power conversion efficiencies (PCEs). Through device engineering and material optimisation, perovskite solar cells have attracted much interest in the scientific and commercial communities due to the fast increase in their PCEs over the past eight years exceeding 20%, rivalling that of silicon based solar cells. The macroscopic properties of these materials and their behaviour in photovoltaic devices has therefore been studied extensively, however the physics and chemistry processes responsible for their good performance are still not fully understood. Femtosecond transient absorption spectroscopy (TAS) allows us to follow the photoinduced population and depopulation of electronic states of perovskite materials on an ultrafast timescale, thereby enabling us to observe the charge dynamics occurring upon illumination in real time. By investigating the charge recombination channels together with their associated rates, we gain a window into the microscopic properties of perovskite photoabsorbers and a step towards learning why they are such good PV materials. In this study, thin films of the high efficiency solar cell yielding perovskite FA0.85MA0.15PbI2.55Br0.45 spin coated on glass substates, were measured using TAS in the visible and infrared spectral regions. By systematically varying the chemical composition of the perovskite material, we observed that FA0.85MA0.15PbI2.55Br0.45 is characterised by a unique transient spectrum. Furthermore, by comparison of the temporal evolution of its spectroscopic signatures, we built a model of the charge recombination dynamics occurring immediately following photoexcitation, and assigned rate constants to the competing geminate and non-geminate recombination processes. Finally, by varying the incident light intensity we were able to access the third competing process, Auger recombination, and obtain rate constants characteristic for a fixed crystal domain of FA0.85MA0.15PbI2.55Br0.45.