Lead-based perovskites, APbX3, achieved over 23 % of efficiency within only 7 years after first their usage in solar cells. Although these lead-based perovskites have rapidly achieved the high efficiency, they have two intrinsic problems to be addressed to be commercialised; toxicity and instability. To address the problems of lead at the same time, new lead-free and air-stable materials such as inorganic materials including bismuth iodide and bismuth- or antimony-based perovskites are emerging. However, the efficiency of the solar cells employing these new materials is relatively low below 5%. This thesis explores these new materials especially bismuth-based perovskite and bismuth iodide inorganic material for their photoelectronic application with improved device performance.

An inorganic material, BiI3 has suitable optical properties for photovoltaic application but due to the short carrier lifetime (180-240ps), it needs structure optimisation to achieve higher device performance. For this, in-situ processed BiSI interlayer was employed to enhance charge-carrier extraction before their recombination and it was monitored by transient absorption spectroscopy. Fabricated solar cell devices showed improved device
performance with the BiSI interlayer.

Regarding bismuth or antimony-based perovskites, large binding energy, high defects and large bandgap are main issues to be addressed. Bismuth/antimony mixed perovskites were fabricated and investigated using a combined experimental and computational approach in a collaboration with the university of Bath. In the study, it was found that Sb mixing reduces the binding energy and it leads to higher solar cell efficiency. By employing 2D bismuth perovskite, improved PLQY obtained and it might come from the reduced defect density.

In addition, nanocrystals (NCs) of bismuth or antimony-based perovskites were fabricated. These perovskites have high binding energy to overcome for the high-performance solar cell application, but this high binding energy can be helpful for high PLQY. Also, the reduced size to nanometre scale brings less defects in NCs and excitons are more prone to recombine radiatively. Therefore, NCs of Bi/Sb perovskite were fabricated to improve their optical property for opto-electronic application. The fabricated NCs were investigated by a range of characterisation techniques.