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1st Supervisor: Professor Martin Dove
2nd Supervisor: Dr Anthony Phillips
Project Title: Local structure of lead halide perovskites for photovoltaic applications.
Fabricating high-efficiency, low-cost and long-term stability solar cells is of significant importance to solve energy problems. Recently, hybrid inorganic−organic lead halide perovskites, with the general formula of ABX3 (A = CH3NH3+, ; B = Pb2+; X = I—, Br—), have become promising for easy fabrication and high power conversion efficiency (PCE). The PCE of such perovskite-based devices has been substantially increased from 3.8% in 2009 to 22.1% in 2016. The high symmetry of the parent perovskite structure ABX3 can be reduced by orientational disorder of methyl ammonium (MA) cations, rotation and distortion of BX6 octahedra. Since this disorder appears to be fundamental to the improved properties of these devices, understanding the crystal structures and phase transitions of perovskite materials can aid in enhancing performance of perovskite materials.
Herein, we combine neutron total scattering with Reverse Monte Carlo (RMC) modelling to investigate the rotational disorder of the MA cations. Total scattering is a combination of the Bragg and diffuse scattering over all scattered energies. This gives the local instantaneous atomic structure, along with the average long-range structure provided by Bragg scattering. This local view is critical to understanding the effects of disorder in these materials. The RMC simulation method produces a three-dimensional configuration consistent with all experimental structural data. For comparison, we have also studied the inorganic analogue CsPbI3 to give information on the effect of different cations within the perovskite structure, and hence to understand this family’s structural flexibility. When all is said and done, we are able to elucidate the relationships between the structural disorder in these materials and their optoelectronic properties, leading towards the goal of rational design of new photovoltaics.
China Scholarship Council (CSC)