Electronic excitations and rational design of novel light sensitisers for photovoltaics

Thesis

The development of scalable and cost-efficient solar cell technologies constitutes a priority in the field of photovoltaics research. Semiconductor sensitised solar cells (SSSC) and hybrid organic-inorganic perovskite solar cells (HOPSC) are two emerging technologies that have been actively pursued in the search for the most efficient, cost-competitive, stable and nontoxic photovoltaic devices. The HOPSCs have been polarising the attention of the photovoltaics community in the past three years due to their ever-increasing efficiencies, currently exceeding 20% while SSSCs have increased in popularity in the last decade, showing a steady increase of their efficiency and emergence of new materials implemented as light sensitisers. Improvement of these novel technologies relies on understanding of the physical properties of the materials components and on efficient strategies towards the discovery of novel compounds. In this thesis, we address these requirements by modelling the electronic structures of novel light sensitisers from first principles. We focus on the analysis of two groups of materials, the hybrid organic-inorganic lead-iodide perovskites and the metal chalcogenides of the stibnite family. We study the electronic structure of CH₃NH₃PbI₃ within density functional theory and obtain the quasiparticle band gap for this material within the GW method in good agreement with experiment. Further, we conduct a systematic study of the interplay between the electronic properties of hybrid organic-inorganic perovskites and the structure of the inorganic perovskite network. As a result, we obtain a simple strategy for tuning the band gap of perovskite light absorbers by changing the size of the central cation, and propose AsH₄PbI₃ and SbH₄PbI₃ as potential novel light sensitisers for HOPSC. The second part of the thesis is dedicated to the study of the electronic structure of four isostructural metal chalcogenides of the stibnite family, stibnite, antimonselite, bismuthinite and guanajuatite. A study of the quasiparticle band gaps of these materials is conducted, similar to the approach used for CH3NH3PbI3. By using the Shockley-Queisser analysis, we obtain that all four materials are promising for application as light sensitisers.

Authors: Filip, M

• DOI: 10.5287/ora-9e90va4no
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford