Solar cells have emerged as a popular and sustainable source of energy in recent years. These cells convert sunlight directly into electricity and can be used to power a wide range of applications, from small household appliances to large industrial complexes. As a result, they are becoming an increasingly popular choice for both residential and commercial applications, contributing to a cleaner and more sustainable future. The present thesis is devoted to investigating three novel monolithic multi-junction structures using TCAD numerical simulation. The proposed cells are: (i) A 2T monolithic all-BaSi2 tandem cell, (ii) A 2T monolithic Sb2S3/Si tandem cell, and (iii) A 2T monolithic polymer/Si tandem cell. Before incorporating the sub-cells into monolithic tandem cells, they are calibrated against experimental studies. Then, performance of the tandem cells is optimized by engineering various parameters such as conduction and valence band offsets, layers thickness and doping concentration, and designing their current matching point. Power conversion efficiencies of 24.21%, 24.34%, and 34.25% are achieved for the optimized polymer/Si, Sb2S3/Si, and All-BaSi2 tandem cells, respectively. These simulation studies are intended to provide tandem configurations that are based on an all-thin-film design which may be suitable for applications like flexible electronics.

Multiwalled carbon nanotubes (MWCNTs) has been synthesized using chemical vapor deposition (CVD) method. Al – Layered Hydroxide (Al–LH) and MWCNTs nanocomposites; (1-x) Al–LH + (x) MWCNTs, 0.0 ≤ x ≤ 1; have been synthesized using citrate nitrate assisted hydrothermal technique. The crystal structure and the functional groups of the prepared samples were examined using X-ray diffraction (XRD) and Infrared spectroscopy (FTIR) respectively. Their layered structure seemed under the high-resolution transmission electron microscopy (HRTEM), and the morphology was observed using field emission scanning electron microscopy (FESEM). Moreover, the synthesized nanocomposites were further characterized using Zeta potential and size analysis and Brunauer– Emmett–Teller (BET) surface area which showed their different character-istics as the MWCNTs content is changed. Thermal gravimetric analysis assured the thermal stability of the nanocomposites over the temperature from room up to 480 °C depending on the MWCNTs content. The obtained results revealed the improvement of all mechanical properties with the in-crease of MWCNTs content.