This project investigated organic and inorganic perovskite solar cells in terms of their design, fabrication, and photovoltaic performance using computational and experimental methods. Bismuth-based perovskites were theoretically explored by employing density functional theory through the Cambridge Serial Total Energy Package software. Perdew-Burke-Ernzerhof exchange-correlation functional for solids was employed to examine structural, electronic, and optical properties of Bi-based perovskites. The crystal structure of Bi-based perovskites was simulated using Jmol and VESTA. Electronic density of states, joint density of states and absorption coefficients were performed using OptaDOS. Additionally, Bi-based perovskite solar cells were fabricated to analyse their photovoltaic performance. The precursor materials were produced using the wet-chemical synthesis method. Diffuse reflectance and transmittance spectroscopy were used to obtain spectral properties of Bi-based perovskites. The energy band gaps of the perovskites were estimated using Tauc plots with the Kubelka-Munk function. The layers of Bi-based perovskite solar cells were structured using spin-coating and sputter-coating methods. Furthermore, degradation and recovery investigations were conducted using lead-based perovskites with titanate nanotubes. The ion-exchange method was utilised for producing lead titanate nanotubes. Pb-based perovskite solar cells with titanate nanotubes were fabricated using the doctor-blading method. Diffuse reflectance and Fourier-transform infrared spectroscopy were used to show the influence of methanamine hydroiodide treatment on degraded perovskites. First principles density functional theory calculations showed that the crystal structure of Bi-based perovskites, which were Cs3Bi2I9, Cs3Bi2Br9 and Cs3Bi2Br3I6, crystallised in the hexagonal space group. The electronic band structure of Cs3Bi2I9 estimated 1.99 eV of Cs3Bi2I9 band gap energy, which was compatible with 2.00 eV band gap energy from Tauc plots. The energy band gap of Cs3Bi2I9 was determined as 2.42 eV and 2.68 eV from the computational and experimental studies, respectively. The current density-voltage characteristics of the Cs3Bi2Brx I9−x solar cells demonstrated that the perovskite solar cell with Cs3Bi2Br3I6 achieved the highest PCE of 0.067% compared to the other Bi-based cells. The degradation and recovery study revealed that methanamine hydroiodide treatment significantly restored the diffuse absorbance response of MAPbI3/Tint and the current density-voltage characteristics of the MAPbI3/Tint solar cells.