The effect of distributed series resistance on the dark and illuminated current—Voltage characteristics of solar cells

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 illuminatedJ-Vcharacteristics of the cell. The equivalent series resistance (rs) in the dark is found to decrease with current densityJfromr_{b} + r_{e}/3at smallJto (r_{e} r_{b})^{1/2}at very highJ, where reand rbare the emitter layer and base region resistances, respectively. For illuminated conditions rsdepends onJas 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 JLfromr_{b} + r_{e}/3tor_{b} + r_{e}/2and the open-circuit value decreases with JLfromr_{b} + r_{e}/3to(r_{e}r_{b})^{1/2}. The variability of rsis therefore related to the relative importance of rbandr_{e};r_{b}plays the role of attenuating this variability, a situation not well recognized previously. Previous theoretical and experimental work is critically reviewed throughout this paper.