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High bandgap lead-halide perovskite solar cells (PSCs) have gained interest as top cells for tandem solar cells and photoelectrochemical applications due to their suitable energy bands. However, the PSCs have limited stability and performance, and their fabrication in a glovebox and utilization of expensive metal contacts increase the cost and limit their application. Therefore, this thesis aims to enhance the efficiency and stability of high bandgap formamidinium lead tribromide PSCs (FAP-bBr3-PSCs), simplify the preparation process, reduce their cost, and explore their application in energy conversion by optimization operation processes in an ambient environment. To achieve perovskite films of superior quality featuring large crystal sizes and high solar-to-electricity power conversion efficiency (PCE), we investigated various techniques, including adding additives and solvent engineering, in preparation of the perovskite. We also built a 2D/3D perovskite interface to passivate the interfacial defects and increase the PCE and stability of the PSCs. In addition, we compared the performance of different dopant-free hole transport materials (HTMs). We found that the polymer P3HT presented superior charge extraction from the perovskite, and high charge transport, resulting in a champion solar cell PCE of 9.4% and improved operational stability. To enhance the stability and decrease the cost of the PSCs, we replaced the hole extraction layer and precious metal electrodes with a carbon electrode. We then used the device to build a monolithic photoanode with a NiFe catalyst layer for direct photo-driven oxygen evolution. To conclude, this thesis focused on improving the efficiency, stability, and cost-effectiveness of FAPbBr3-PSCs. We achieved the targets by optimizing the fabrication process, passivating interfacial defects, and using alternative materials for the hole extraction layer and electrodes. The results suggest that the high bandgap FAPbBr3 perovskite material shows promising applications in solar and photoelec-trochemical cells.