The technological gap in producing flexible silicon solar cells on metal substrates is addressed in the silicon based thin film solar cells on flexible metal substrates (SiSOFlex) project. The goal of the project is to investigate and determine the influence and interaction of the different components of the solar cell such as the substrate, the front and back contacts and the encapsulation to develop a working solar cell. To this end, this research work focuses on optical simulations of flexible silicon solar cells by solving Maxwell’s equations numerically. Consequently, different classes of simulations are performed in close coordination with experimental and project development stages. The first class of simulations are optimization simulations which focus on parameters such as surface roughness, active layer thickness, front contact type and structure of the solar cells. The second class of simulations are concept suggestion validation simulations which are done to verify the validity of different performance improvement concepts. The third class of simulations are comparison simulations which are performed to compare and verify the simulation and the experimental results. In the following, the main modelling techniques which have been proposed in this thesis for each class of simulations are discussed. In the optimization simulations, the encapsulation layer plays an important role in the performance of the solar cell. The encapsulation layer increases the total reflection thereby reducing performance. In order to analyze this, thick encapsulation layers, with thickness > 300� m, are modeled and simulated by developing a new technique that divides the solar cell in two parts. The top part, containing the encapsulation and the glue layers, is modelled by the transfer matrix method and the bottom part, with the remaining layers, is modelled by the Finite Difference Time Domain (FDTD) method. The proposed technique combines these two parts and simulates the complete solar cell. The simulation results show that, the total reflection from the solar cell increases due to the encapsulation layer which in turn reduces the efficiency of the solar cell considerably. In the concept suggestion validation simulations, interface roughness is of great interest due to its ubiquitous appearance in the light trapping field of thin film solar cells. In order to perform a sound analysis of the effect of interface roughness as a light trapping technique, a new Fourier Transform based surface texture synthesis method is developed. This method is used in the simulations and analyses of surface texture at different interfaces in the solar cell. From the simulations and the analyses, it has been shown that the front contact roughness of a solar cell has a dominant influence on the efficiency than the back contact roughness. In a further analysis of the effect of interface roughness on the performance of single junction amorphous silicon solar cells, the interface roughness has shown different effects on the efficiency depending on the size of the structures and the location of the interface. At the front contact, the micro parts of the roughness affect the performance of the solar cell more than the macro parts. At the back contact, both the macro and micro parts do not significantly affect the performance given optimized roughness at the front contact. In comparison simulations, the scattering property of the substrate is particularly interesting and difficult to simulate because of the interplay between the size of the simulation and the computational resource needed. In this thesis, the scattering property of the substrate is described by the angularly resolved scattering (ARS). Simulation of ARS from a metal substrate covered with transparent conductive oxide using numerical methods such as Finite integration technique with time harmonic inverse iteration technique requires huge computational resources. To overcome this, a ray tracing method is used in this thesis. The ARS simulated using the proposed ray tracing method shows that the surface roughness results in a zero direct reflection and a high diffuse reflection. This is in good agreement with the measured ARS from experiments. The modelling, simulations and optimizations works done in this thesis have played an indispensable role in producing a working flexible silicon solar cell on an aluminum substrate with an efficiency of 11%.