Determining diode parameters of illuminated current density-voltage curves considering the voltage-dependent photo current density

Photovoltaics Group, Martin-Luther-University Halle-Wittenberg, 06120 Halle (Saale), Germany

^a e-mail: florian.obereigner@physik.uni-halle.de
^b e-mail: roland.scheer@physik.uni-halle.de

Received: 13 September 2013
Accepted: 11 December 2013
Published online: 5 February 2014

Abstract

Suitable procedures for the determination of diode parameters of illuminated and dark current density-voltage (j-V) curves of solar cells are investigated. Within these procedures we avoid misinterpretations by the commonly used shifting approximation which assumes a voltage-independent photo carrier collection. To this end, the voltage-dependent collection efficiency is determined by j-V measurements under incremental illumination. After that, illuminated curves can be converted into dark curves taking the voltage-dependent photo current density into account. The converted dark curve next is consigned into a program that numerically solves the implicit equation of the current density and derives the diode parameters by means of a weighted least-squares minimization. Only if fluctuations of the illumination are noticeably high this procedure cannot be used, since the converted dark curve also reveals a high noise level. Then, the determination of diode parameters is performed stepwise with the help of commonly used methods.