Understanding dimensionality in thin film solar cells

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This project will focus on fabrication and analysis of thin films and solar cells using materials with different dimensionality. By directly comparing 1D, 2D and 3D lattice materials we will determine what role their structure plays on carrier transport, defect formation and ultimately solar cell performance. The student undertaking the project will be based in the Stephenson Institute for Renewable Energy (SIRE). Solar cell platforms for CdTe, Sb2Se3 and GeSe are already established in SIRE and they will become an expert in thin film deposition and solar cell fabrication using these materials, as well as associated structural and device level analysis techniques. The current market-leading thin film solar cell technology cadmium telluride, CdTe, is a material with a typical 3D crystal lattice. Because thin films have a polycrystalline grain structure this means they invariably contain grain boundaries. For 3D lattice materials, grain boundaries become sources of high recombination due to the presence of dangling bonds which need to be carefully passivated for the material to function1. This adds additional complexity and cost to the production process and even with passivation, the grain boundaries remain limiting. Recently research focus has been on the possibility of using lower dimensional materials as a way to minimise the impact of polycrystallinity on solar cell performance. Antimony selenide, Sb2Se3, solar cells are a key example of this having rapidly developed in performance due to their 1D nano-ribbon crystal structure, where covalently bonded ribbons are held together via Van der Walls bonds. 2D nano-sheet materials such as germanium selenide, GeSe, are at an even earlier stage of development and consequentially even less well understood but similarly show a high degree of promise as a next-generation solar cell material. There are still a number of questions on the extent to which the low-dimensionality benefits thin film materials to be answered: How much does orientation or the ribbons/sheets control carrier transport, do they actually have reduced electronically active defects, what role does grain structure play, how far can solar performance be taken?This project will focus on the fabrication and analysis of thin films and solar cells using materials with different dimensionality. By directly comparing 1D, 2D and 3D lattice materials we will determine what role their structure plays on carrier transport, defect formation and ultimately solar cell performance.