Thermal Design, 2nd Edition

7Solar Cells

7.1 INTRODUCTION

Solar cells, sometimes referred to as photovoltaic (or PV) cells, are semiconductor devices that convert sunlight directly into electric current to produce useable electric power. As long as light is shining on the solar cell, it generates electrical power. Some have been in continuous outdoor operation on Earth or in space for over 30 years.

The photovoltaic effect in liquid electrolytes was discovered in 1839 by Becquerel, and the first functional PV device was made by Fritts [1] in 1883 using a selenium film. The modern solar cell was accidently discovered in Bell Labs in 1954 by Chapin et al. [2] with a 6% efficient silicon p–n junction solar cell. The most famous early application of solar cells in space was the Apollo 11 moon mission in July 1969. In the 1970s, the goal was to break a 10% barrier of solar cell efficiency. After continuous development, a world record of 40.7% efficiency was reported in 2006 using a concentration of 240 suns by Boeing‐Specrolab using triple‐junction GaInP/GaAs/Ge solar cells. Commercial solar cells usually appear with a lower efficiency in the years following development in research labs.

The most widely used materials for solar cells are single crystalline silicon (c‐Si) and polycrystalline silicon (poly‐Si), which are both referred to as crystalline silicon. The single crystalline and polycrystalline materials are also called monocrystalline and multicrystalline materials, respectively. Crystalline silicon ...