A Study on Conjugated Polymer Photovoltaic Devices and Components

Investigating Trapping Effects and Mobility in Conjugated Polymer Photovoltaic Devices

Abstract

In solar cells based on amorphous silicon traps play adominant role in the description of the solar cell characteristics. Incontrast, the current in OC1C10-PPV based hole-onlydiodes has been shown to depend quadratic on voltage and exhibit a third powerdependence on sample thickness. This behavior is characteristic for aspace-charge limited current (SCLC). The occurrence of SCLC enables us todirectly determine the hole mobility from the current voltage characteristics.It should be noted that a material with shallow traps would also exhibit anidentical voltage and thickness dependence, and the observed mobility would bean effective mobility in that case, including trapping effects. However,transient measurements demonstrated that the measured mobility does not showany evidence of trapping effects. The same holds true for the electrontransport in bulk PCBM. Additionally, the electron and hole mobility in theblend of both materials have been addressed, both showing trap-free SCLcurrent-voltage characteristics. Therefore, it can be safely concluded thattrapping effects do not play a role in our devices, and hence can be neglectedin our model.