The Solar Cell and the Electrochemical Cell
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We derive the conversion efficiencies of solar cells under various conditions in the chapters following Chap. 3. For our discussions on the solar cell conversion efficiency, it is extremely important to first understand the principle of electricity generation in a solar cell. In contrast to the electrochemical cell, which is usually introduced in high-school grade chemistry, the opportunities to study the operation principle of solar cells are almost zero except for some specialized schools. Most solar cells consist of a semiconductor p–n junction, which is a connection between a semiconductor n-layer with many electrons and a semiconductor p-layer containing plenty of holes in the semiconductor crystal. Even if high-school lectures on solar cells could be established, we have in mind that the explanation of how the electricity generation exactly works in such solar cells often will have to be skipped and summarized as “knowledge belonging to the category of semiconductor engineering.” On hearing the rather famous word semiconductor, one may think of realms of science completely different from the electrochemical cell. Since there are too many things that have to be learned regarding semiconductor materials, many of those who try studying the operation principle of solar cells may have difficulties to immediately grasp all essential relations. In this chapter, we explain how the solar cell converts the energy supplied by the Sun into electrical energy. For this, we employ the example of the well-known electrochemical cell, in particular, the “voltaic pile” which was most likely studied first in high school, and compare it with the solar cell from the viewpoint of the redox reactions. In order to easily grasp the idea of how current flows, the explanations especially emphasize the electron movement that occurs inside the solar cell. After explanation of the operation principle of the voltaic pile on a high-school chemistry level in Sect. 1.1, we explain the principle of electricity generation in a solar cell while outlining the parallels to the electrochemical cell. Finally, we clarify the unique qualities of the solar cell by discussing the similarities and differences between these types of “cells,” i.e., the electrochemical cell and the solar cell.