Electrode and interface materials for tin perovskite photovoltaics

The first results chapter of this thesis reports the development of a novel Ni passivated Cu grid electrode fabricated by microcontact printing, and demonstrates its use as the transparent electrode in tin perovskite photovoltaic devices (PPVs) as an alternative to the conventional indium-tin oxide (ITO) electrode. It is shown that this novel electrode design addresses the two challenges associated with using Cu-based electrodes in PPVs: migration of Cu into the perovskite layer and the oxidation of Cu in air. The second results chapter reports unencapsulated organo-halide tin PPV devices exhibiting record stability when tested under continuous one sun simulated solar illumination in ambient air and under electrical load which is made possible by using a bathocuproine | Cu top electrode. A series of experiments designed to elucidate the underlying reasons for the high stability show that, compact Cu electrodes are far more resistant to corrosion by iodine gas and towards the adverse morphological evolution. The third results chapter presents the findings of a study aimed at assessing the suitability of CuSCN as a hole-transport layer in inverted PPV devices based on the B-γ phase of CsSnI3 perovskite. It is shown that when B-γ-CsSnI3 perovskite is deposited from a N,N-dimethylformamide solution onto a thick CuSCN film supported on an ITO electrode, the CuSCN layer is completely displaced leaving a perovskite layer with high uniformity and coverage of the underlying ITO electrode. This finding is confirmed by detailed analysis of the thickness and composition of the film that remains after perovskite deposition, together with PPV device studies. The fourth results chapter explores the possibility of improving the intrinsic stability of CsSnI3 perovskite by partial substitution of Cs with Rb and partial substitution of I with Br. Substantial improvements in perovskite stability towards oxidation in ambient air, followed via the evolution of the electronic absorption spectra, together with a potentially beneficial increase in ionisation potential measured using photoelectron spectroscopy, were achieved for the composition Cs0.8Rb0.2SnI1.5Br1.5. The final results chapter reports preliminary results relating to the development of a nano-contact substrate electrode as a new approach to charge extraction layer design in PPVs