Electrical energy is used at approximately the rate of 15 Terawatts world-wide. Generating this much energy has become a primary concern for all nations. There are many ways of generating energy among which the most commonly used are non-renewable and will extinct much sooner than expected. Very active research is going on both to increase the use of renewable energy sources and to use the available energy with more efficiency. Among these sources, solar energy is being considered as the most abundant and has received high attention. The mobile phone has become one of the basic needs of modern life, with almost every human being having one.Individually a mobile phone consumes little power but collectively this becomes very large. This consideration motivated the research undertaken in this masters thesis. The objective of this thesis is to design a model for solar power based charging circuits for mobile phone using Simulink(R). This thesis explains a design procedure of solar power based mobile charger circuit using Simulink(R) which includes the models for the photo-voltaic array, maximum power point tracker, pulse width modulator, DC-DC converter and a battery. The first part of the thesis concentrates on electron level behavior of a solar cell, its structure and its electrical model.The second part is to design an array of solar cells to generate the desired output. Finally, the third part is to design a DC-DC converter which can stabilize and provide the required input to the battery with the help of the maximum power point tracker and pulse width modulation. The obtained DC-DC converter is adjustable to meet the requirements of the battery. This design is aimed at charging a lithium ion battery with nominal voltage of 3.7 V, which can be taken as baseline to charge different types of batteries with different nominal voltages.