Growth of Sb2Se3 Thin Films by Vapour Transport Deposition for Inorganic Solar Cells

The development of new materials and manufacturing technologies for photovoltaic (PV) power generation is vital for transitioning to a renewable and cleaner energy economy. The use of PV panels to produce electricity has spiked globally, rising by 12-fold in only 10 years. Emerging photovoltaic materials, which can be processed via simple and low-cost solution or evaporation methods, have the potential to significantly reduce manufacturing costs and in-crease the efficiency of solar cells for the realisation of low-cost-high-efficiency commercial solar panels. Novel PV materials have improved remarkably fast, within only a few years of development perovskite-based devices achieved power conversion efficiencies (PCE) that are on a par with the best single crystal silicon solar cells. Antimony chalcogenides (Sb2(S, Se)3, Sb2S3 and Sb2Se3) have recently emerged as an excellent light absorbing material for thin film PVs. The selenide phase (Sb2Se3) has garnered special attention as Sb2Se3 solar cells have recently surpassed the 10% efficiency benchmark. Still, this material technology requires significant improvements to be competitive. Major challenges facing Sb2Se3 devices are related to poor interfaces and to the requirement to favourably align the quasi-1D (Sb4Se6)n ribbon crystal structure. This thesis investigates and explores solutions to these issues over three main experimental chapters. Firstly, an in-depth experimental investigation into the effect of employing different high resistance metal oxide (HRMO) layers on the quality of the front contact in superstrate Sb2Se3 solar cells is presented. The crucial role of HRMO in preventing shunting and maintaining device stability is verified, followed by an investigation into the generation/suppression of de-fects and the presence of electron barriers. Second, it is shown for the first time that substrate nanostructure plays a key role in driving the growth of (001) oriented Sb2Se3 thin films. An in-depth study on the mechanistic origin of oriented film growth on highly nanostructured substrates is presented, wherein Sb2Se3 orientation was found to be independent of substrate surface chemistry. Finally, the templated growth of (001) Sb2Se3 thin films as a viable method for device fabrication is demonstrated through the fabrication of rigid and flexible photodetec-tors and a proof-of-concept flexible heart rate detector. Overall, the investigations presented in this thesis are essential to guide the further development of high-quality Sb2Se3 solar cells and to overcome fundamental challenges in the fabrication of high quality Sb2Se3 layers with controlled morphology and orientation.