Modeling of photoactive area spreading in unstructured photovoltaic cells

Abstract

In this work the influence of unstructured charge-extraction/transport layers on solar cell photocurrent measurements is investigated. Photovoltaic cells incorporating unstructured conductive layers exhibit a significant amount of photoactive area spreading. This can lead to a large error in determining solar cell short circuit current density and fill factor from I-V measurements. To counteract this effect an analytical model is developed to describe the photoactive area spreading. The developed model requires only solar cell contact geometry and transport layer sheet resistance in order to calculate the spreading current from measured I-V data. Thus total removal of unwanted spreading current from experimental data and calculation of realistic solar cell efficiency is achieved. As an example this model is applied to unstructured metal mesh based organic solar cells, and presented data show that it yields more accurate results compared to the conventional shadow masking approach.