Optical and electrical modeling of polymer: fullerene bulk heterojunction solar cells

PhD ceremony: Mr. J.D. Kotlarski, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Optical and electrical modeling of polymer: fullerene bulk heterojunction solar cells

Promotor(s): prof. P.W.M. Blom

Faculty: Mathematics and Natural Sciences

Because the worldwide demand for usable energy increases yearly, feasible and renewable sources that meet this demand need to be employed. One candidate is the field of photovoltaics, where light absorbed in a semi-conductive material is directly converted to electric current. A relatively new subfield utilizes specially prepared plastic layers in so called organic solar cells to harvest sunlight. Typical organic solar cells have two materials employed in the conversion of photons into extractable charge carriers, often a polymer absorbing photons that are converted into excitons and a fullerene extracting electrons from the polymer’s excitons. In most cases both materials are intermixed as a bulk heterojunction to obtain a larger interfacial area between the materials and have shorter exciton travel distance to that interfacial area. A combined optical and electrical model can be used in order to simulate the electric behavior of organic solar cells containing polymer:fullerene BHJ active layers and their efficiency. In this thesis the principles of optical and electrical modeling are reviewed, the influence of the exciton generation profile on the performance of solar cells with imbalanced charge transport is shown, the importance of balancing charge transport for small band gap solar cells is demonstrated, the influence of the active layer charge transport on structure choice for single and tandem cells is shownand the optimization of single and tandem cells is investigated by varying polymer band gaps and active layer thicknesses.