**1. Introduction**

20 Will-be-set-by-IN-TECH

230 Solar Cells – New Aspects and Solutions

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Zhou, D., Sharma, G., Thomassen, S. F., Reenaas, T. W. & Fimland, B. O. (2010). Optimization

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towards high density quantum dots for intermediate band solar cells grown by

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The storage of solar energy is one of the key technologies in making solar energy a major energy resource for humans (Turner et al., 2004). Solar hydrogen, which is produced by splitting water using solar energy, can be considered the perfect renewable energy. Hydrogen is an energy medium that can be easily stored and transported. It can generate not only thermal energy but also electricity using fuel cells and mechanical energy using hydrogen engines. Hydrogen returns to water via such energy generation. Therefore, solar hydrogen can form the basis of a clean, renewable energy cycle.
