The Effect of Distributed Series Resistance on the Dark and Illuminated Current-Voltage Characteristics of Solar Cells

Abstract

Distributed series resistance effects in solar cells are analyzed and the correctness of representing these by a lumped parameter is discussed for any conditions of bias and illumination. In addition to a general mathematical methodology, analytical expressions are derived to simplify the estimation of series resistance effects on the dark and illuminated I-V characteristics of the cell. The equivalent series resistance (rs) in the dark is found to decrease with current density J from rb + re/3 at small J to (rerb)1/2 at very high J, where reand rb are the emitter layer and base region resistances, respectively. For illuminated conditions rsdepends on J as well, being maximum near short-circuit and minimum near open-circuit; however, rsfurther depends on the photogenerated current JL: its short-circuit value increases with JLfrom rb + re/3 to rb + re/2 and the open-circuit value decreases with JLfrom rb + re/3 to (rerb)1/2. The variability of rsis therefore related to the relative importance of rhand re; rbplays the role of attenuating this variability, a situation not well recognized previously. Previous theoretical and experimental work is critically reviewed throughout this paper. Show more