In this research we investigate the fill factor of polymer: fullerene bulk heterojunction solar cells through a novel approach. We relate the fill factor with the ratio between the rate of bimolecular recombination of free charge carriers and the extraction of free carriers at the electrode, which we define as ?. The parameter ? depends on the properties of the material and the device; i.e., in the mobilities of single and double carrier devices. Through computational simulations  we found a trend for the FF-? curve. We fabricate organic solar cells (OSCs) and single carrier devices. Then we collect experimental values of ? and FF to confirm the predicted FF-? trend. The key experiment is the measurement of the current-voltage curve (J-V) curves for both devices without illumination and for the OSCs under illumination. We characterize the OSCs by their dependency to the light intensity and their thickness, at three different temperatures. We successfully confirm the predicted trend, assuming bimolecular recombination as the dominant mechanism that determines the FF. We discuss deviations to the predicted FF-? trend and we propose that they are caused by the presence of trap assisted recombination of free charges.
|Date of Award||31 Aug 2014|
|Supervisor||D. Bartesaghi (Supervisor 1), L.J.A. Koster (Supervisor 2) & René A.J. Janssen (Supervisor 2)|