A Theoretical model for Conjugated Polymer Solar Cells

Abstract

The fossil oil has been the primary source energy which the modern human society relies on. Recently, the price of crude oil increase dramatically and it impacts the global economy and the livelihood of the people. To solve this problem, it is necessary to develop other inexpensive energy sources to reduce our dependence on oil. Therefore searching for alternative energies is an important issue. The solar cell has great potential among the numerous alternative energy sources, because it directly captures the solar energy from the sun and does not release chemical pollutant during operation. There are many types of solar cells on the market. The conjugated polymer solar cell is a new generation of solar cell at the present. Although its development started very recently, it has attracted a significant amount of attention because of a lot of advantages, especially its low cost and the ease of fabrication. However, the low efficiency (currently about 6%) problem has been a big challenge for the conjugated polymer solar cell and makes it impossible for commercialization. If we can have a mathematical model to describe the internal mechanism inside the cell, it would be helpful to find the optimal design of the conjugated polymer solar cells. In this thesis, we developed a numerical model for polymer/fullerene bulk heterojunction solar cell. Using this model, we can simulate the electric performance of solar cell and the result is consistent with experimental current-voltage curve. On the other hand, we can analyze the distribution of physical properties to better understand the distribution and transport of electrons and holes inside the solar cell. Based on the good agreement with experiments, the prediction of solar cell''s efficiency can be calculated by changing the material''s parameters in the model. Our analysis suggests that the key factors for the efficiency are orbital energies of materials. Finally, the mathematic model can also offer an efficiency table for the new material development to solve the low efficiency problem.