Chapter VI - Solar Cell Configuration and Performance

Abstract

This chapter discusses various solar cell optical orientations and construction techniques. It determines the value of solar cell series resistance, saturation current, optimum junction voltage, maximum power density delivered to the external load, and the value of the optimized external load with the help of specific semiconductors. The characteristics of pn and heterojunction solar cells depend primarily on the properties of the semiconductor(s) employed. The most important semiconductor property in these cases is the width of the energy gap. For all types of solar cells the charge carrier mobility and lifetime play major roles in overall performance. The standard configuration solar cell is simple to construct and has good contact from solar cell to heat sink. However, it has a number of drawbacks as well. Once the electron-hole pairs are generated, they must be split into their component electrons and holes and the individual charge carriers must be collected by the junction. The thinness of the upper layer of the solar cell creates high internal resistance with attendant decreased power performance. PN junction solar cells also show ill effects from this phenomenon, but heterojunction solar cells avoid the problem by constructing the “front layer” of the solar cell of a semiconductor, which is optically transparent. The chapter also examines both standard and inverted configurations in detail, making use of six example semiconductors.