Investigations on Tin-Containing Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) have advanced from 3.9% efficiency in 2009 to 26.9% in 2025, emerging as low-cost, scalable alternatives to silicon photovoltaics. Their potential to meet rising energy demand and help address climate challenges has sparked unprecedented academic and industrial interest. However, most PSCs rely on lead (Pb) in their composition, raising toxicity concerns. While tin (Sn)-based perovskites offer a non-toxic alternative, their performance still significantly lags behind that of their Pb-based counterparts. In this thesis, Sn-containing halide perovskite thin films and solar cells, either purely Sn-based or Sn–Pb mixed, are fabricated and thoroughly investigated, with the aim of gaining a deeper understanding of these materials through the identification of their challenges, as well as proposing practical strategies to improve thin film quality and device performance. The results presented include the development of in-house Sn-based PSC fabrication protocols yielding power conversion efficiencies (PCEs) of up to 8.35% with good repeatability, along with insights into the chemical and physical mechanisms behind performance improvements enabled by bulk additives, interfacial modifications, and surface post-treatments. The role of energy level alignment between hole-selective layers and mixed Pb–Sn perovskites is clarified, and a tandem solar cell (TSC) featuring a narrowbandgap, Sn-containing subcell with a PCE of 25% is demonstrated as proof of concept. Comprehensive insights are gained across all perovskite thin films and solar cells analysed in this thesis. Microscopy, diffractometry, and advanced spectroscopic techniques are combined with standard electrical characterization methods to provide a full picture of the studied systems, enabling the proposal of simple mechanistic models. Key findings include the interaction of Sn2+ ions in the perovskite bulk with Cl– from additives, leading to improved film quality, and the revelation of a complex interplay of charge extraction and interfacial phenomena at the Pb–Sn perovskite/hole-transporting interface.