الفهرس 
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Abstract
Solar cells have been proven to be a valuable mean to convert the energy provided by the most substantial, accessible and reliable source of renewable energy, the solar radiation, into electricity. According to the environmental perspective, the use of renewable energy helps in decreasing the amount of environmental and global issues caused as a result of the massive use of fossil fuels. Moreover, the running cost of units such as solar cells is a way less expensive than the use of traditional power generating units. However, using solar cells is still limited by their poor light power conversion efficiency (PCE) for most kinds of solar cells. The most widely used kind of solar cell is the silicon-based cells, forming about 86% of the current global market, however, they still need to be replaced or at least get modified, for their poor value of PCE, as it has not exceeded the value of 27.6%, to be able to get along with the massive need of energy needed in the world every day. Motivated by the urgent need to improve the PCE of solar cells, many methods have been introduced as a solution of poor efficiency problem; light trapping is one of the most promising solutions. The light trapping in solar cells may be defined as an optical mechanism used to capture the maximum possible amount of incident light and keep it within the cell structure for the longest possible time. It is extremely needed to maintain the light inside the structure of solar cell, as this increases the probability of electron-hole pairs’ generation, that in turn leads to increasing the efficiency of the solar cell; in other words, The light trapping concept with all its forms in solar cells mainly concerns with achieving higher short current density level denoted by generating more electron hole pairs. In this thesis, we consider the semiconductor physics and solar cells numerical model and the working principle, and then we chose two types of the third generation solar cells that hold the promise of high PCE, namely, Intermediate band solar cells (IBSCs) and Perovskite solar cells (PSCs), and theoretically considered improving their PCEs even more with the aid of different light trapping techniques. Our first study is IBSCs with front pyramid surface grating, Results show that maximum efficiency of the proposed model of IBSC with frontal surface grating is 58.15% with short circuit current density of 49.03 mA/〖cm〗^2, while the efficiency of flat surface IBSC is 46.81%, meaning that the power conversion efficiency has been improved by 11.34% in this case. The maximum value of output power observed in pyramid grated surface IBSC is 58.15 mW/〖cm〗^2 with about 11.28 mW/〖cm〗^2 higher than its value for the flat surface one. The second study is PSC with front surface nanospheres grating. Results show that maximum efficiency of the proposed model of PSC with frontal surface grating is 26.06%, with short circuit current density of 31.6 mA/〖cm〗^2, while the efficiency of flat surface PSC is 21.9%, meaning that the power conversion efficiency is improved by 4.16% in case of surface grated cell. The maximum value of output power observed in grated surface PSC is 26.058 mW/〖cm〗^2, about 4.158 mW/〖cm〗^2 higher than its value for the flat surface cell reported in previously published relevant literature. All the proposed designs and results in this thesis have been implemented using the 3D FEM simulation by COMSOL Multiphysics, and then imported to MATLAB in order to either compare between results or find some parameters values.