Study of recombination Models in Organic Solar Cells

Supervisor: Mr. Ananth Saradhi

Duration: May 2012 - July 2012

Project Overview

Photovoltaic effect in inorganic semiconductors is due to the basic phenomenon of excitation of electrons from the valence band to the conduction band when struck with light. Solar Cells have always been tradtionally made from inorganic substances like silicon. However, there has been a recent increase in research in thin film polymeric solar cells, with an aim of reducing the overall cost, efficiency and ease of installation. Morover flexible cells can also be fitted on curved surfaces like the body of an airplane.The field of organic photovoltaics(OPV) has grown as part of third generation PV.In fact, the award of the Nobel prize to Alan Heeger together with Alan MacDiarmid and Kideki Shirakawa for the development of conductive polymers was a major impetus for organic electronic device research.

types of solar cells After understanding the electronic processes going on inside semiconductr devices like doiodes and transistors, the world of solar cells fascinated me highly. So I took up a study oriented project with my lecturer Mr. Ananth Saradhi, whose research was in the area of organic solar cells. The basic aim of my study was to understand the recombination processes that take place in organic solar cells. There are three basic types of organic solar cells, namely bilayer, checkerboard and heterojunction(mixed layers). My study was specially concerned about the bulk-heterojunction solar cells.Later on I also tried to implement the mathematical models of recombination to carry our simulations.

Initially I put a lot of stress is in understanding the phenomena behind current generation using solar cells, specially organic solar cells. This includes photon trapping, charge carrier generation, transport and collection at electrodes. Such an understanding is required to understand the role of recombination processes. In due course, I learnt about various models of charge transport, like Mott's variable range hopping and Ambegaokar's percolation approach, and finally about the recombnation models like, 3D Langevin recombnation and 2D langevin recombination. During this entire study, one of my major sources of knowledge was Dr. Deibel's blog on disordered matter.

I read a few papers in the related field to build up a literature review and towards the end, we also made efforts to understand the use of the software "Athena" provided my Silvaco, for carrying out simulations.