Hybrid lead (Pb) halide perovskites have emerged as greatly promising materials for future optoelectronics, although the toxicity of Pb is currently a major roadblock to the commercialisation of this novel technology. For this reason, less toxic, lead-free perovskite alternatives are of great interest, being hybrid tin (Sn) halide perovskites the highest performing option. Nevertheless, Sn2+ spontaneously oxidises in air to Sn4+, which causes poor stability and excessive non-radiative recombination in these materials. Hence, addressing these issues is needed for further advances in Sn perovskite technologies. This thesis explores the fabrication and characterisation of solution-processed Sn perovskite thin films for light-emitting and photovoltaic applications. Particularly, this work aims to find routes towards higher stability, gain understanding of degradation processes and elucidate the charge separation and recombination dynamics in these systems.
In the first part of this work, we report 2D (PEA)2SnIxBr4-x (PEA ≡ phenylethylammonium) tuneable visible emitters with higher intrinsic stability and superior photophysical properties than conventional 3D Sn perovskites. As a proof of principle, we achieve red electroluminescent devices based on (PEA)2SnI4, elucidating a viable path towards more stable Sn perovskite optoelectronics. Next, we reveal the link between SnI4 impurities in SnI2 perovskite precursors and the degradation of (PEA)0.2(FA)0.8SnI3 (FA ≡ formamidinium) films employed in solar cells. We show that SnI4, also a product of the O2-induced degradation of Sn perovskite, can quickly evolve in ambient conditions into I2, which is found to further oxidise perovskite to more SnI4 and establish a cyclic degradation mechanism. With this knowledge, we provide important solar cell design rules to contribute towards the stabilisation of Sn perovskite. Lastly, charge recombination dynamics in TiO2/Perovskite/Spiro-OMeTAD junctions is studied via Transient Absorption Spectroscopy by employing several 2D/3D Sn perovskite absorbers. Interfacial charge separation at these interfaces is found to be limited by the 2D character of the perovskite, which emphasises the impact of carefully controlling the 2D/3D ratio to achieve efficient Sn perovskite solar cells.