Date of Award

9-2010

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Electrical and Computer Engineering

Supervisor

M. Jamal Deen

Co-Supervisor

W. Ross Datars

Language

English

Abstract

The energy crises, along with the recent global warming trends, demand an immediate cut in the use of fossil fuel. Therefore, renewable sources of energy and especially solar power, have gained tremendous attention from the consumer countries as a possible candidate to replace the carbon-based energy supplies. Among all different types of solar cells, flexibility, cost-effective fabrication processes, combined with low-price materials and most importantly a great potential for improvement make organic solar cells an interesting topic for research. On the other hand, modeling provides a valuable opportunity to study device properties that experimentally are out of reach, expensive or need a long time to measure. These mentioned reasons motivated us to choose modeling of organic solar cells as the subject of our research.

In this research, we tried to provide a complete study of the power generating procedure in organic solar cells by modeling all of the following processes: in-coupling of the photons, absorption of the photons, formation of the excitons, diffusion of the excitons, dissociation of the excitons, transportation of the charges and collection of the charges at the electrodes.

To get a better understanding and also because of basic physical differences, the modeling is
divided into two parts: the optical section and the electrical section. Each section is also divided
into two separate segments, analytical and numerical analysis.

Using the optical models with different designs to improve the performance of the solar cells, the effect of the layer thickness and two- and three-dimensional light focusing apertures on the intensity of light at the junction of n-type and p-type materials (for bilayer heterojunction organic solar cells) are studied. Results show that for a certain design of the light focusing aperture, a 98% increase in the light absorption in a bilayer heterojunction solar cell can be obtained.

The electrical performance of organic solar cell is also studied by using analytical modeling of exciton diffusion for bilayer heterojunction solar cells and numerical models based on driftdiffusion procedures by using COMSOL multiphysics software for bulk heterojunction solar cells. Based on the mismatch between the calculated results and measurement (counterdiode effect), a tunneling current correction is introduced. Finally, using the tunneling current model, the energy diagram of the organic active layer at the metallic contact is characterised.

In summary, five different models are described in five separate sections, and at the end of each section, results are reported and compared with the literature that prove that the presented models can be used for a new design of organic solar cell characteristics to improve the performance of the device. Also, by introducing the tunneling current to model the counterdiode effect, we have contributed to the literature.

McMaster University Library

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