In the last decade, metal halide semiconductors have emerged as promising materials for solar cell applications. While lead halide semiconductors have achieved remarkable power conversion efficiencies, now exceeding 26%, Pb(II) toxicity and stability issues have raised the urgency of developing stable and environmentally friendly alternatives. As a result, a catalogue of emerging metal halide semiconductors (e.g., 2D perovskites, double perovskites, rudorffites, and others) has been the subject of intense investigation. However, record power conversion efficiencies for this new class of materials currently lag behind those of traditional metal halide perovskites, prompting new research efforts to explore and eliminate current performance limitations. In this talk, I will discuss the impact of electronic and structural dimensionality on charge-carrier transport and recombination in these materials.

I will start by discussing the impact of low (<3D) electronic dimensionality on charge-carrier transport in emerging perovskite-inspired materials. Focusing on the archetypal silver-bismuth-based perovskite-inspired materials (PIMs), I will examine how rapid decays in terahertz photoconductivity and their temperature dependence reveal an ultrafast localisation of free charge carriers to a small polaronic state.[3,4] Examples related to several structural and chemical features of PIMs, such as cation disorder, cation vacancies, and structural dimensionality, will be given.

I will proceed in discussing how the peculiar electronic structure of PIMs, and in cases, the presence of localised states, contribute to determining the charge-carrier recombination dynamics of these materials. In particular, I will focus on quasi-1D bismuth-based semiconductors. I will illustrate how temperature-dependent terahertz photoconductivity can disentangle different contributions to overall recombination, and demonstrate how the resulting mechanism can be investigated by comparing the temperature-dependent absorption coefficient with the terahertz photoconductivity through the van Roosbroeck-Shockley equation.

Overall, achieving efficient charge-carrier transport and slow charge-carrier recombination remains a formidable challenge for low-dimensional electronic and structural materials and their use in renewable energy. The findings presented in this talk explore the underlying causes of these challenges, thus tracing a clear path towards tackling them.