Plastic Solar Cells

With the world’s population is growing so quickly, how will we all be supplied with electricity sustainably? Reserves of all the major fossil fuels are dwindling more and more rapidly due to demand increases.

As these supplies diminish, they become impractically expensive for more and more people. Plus, there is global warming to deal with! Fortunately, solar panels don’t automatically become more expensive when electricity demand increases. When you buy your own solar panels, you lock in your electricity rate for the next 30 years or more!

Exceptional fill factors arise from high levels of order in the mixture of polymer donor chains and buckyball acceptor components, the way these two components are distributed within the cell active layer, and a "face-on" orientation of the polymer chains on the electrode surface.

The fill factor achieved is more than 10 percent greater than previously achieved by the polymer solar cell community, and, in the present study, although the polymer semiconductors have non-optimal light absorption characteristics, a near-record power-conversion efficiency as high as 8.7 percent is still obtained.

The working principle of polymer solar cells differs greatly from that of traditional silicon solar cells. The active layers of polymer solar cells typically contain a mixture of polymer chains that can donate electrons and "buckyball" molecules that accept electrons. (Buckminsterfullerene, or buckyball, is a spherical fullerene molecule with the formula C60.)

Under solar irradiation, electronic excitation generates mobile electron-hole pairs called excitons. The excitons then diffuse through the active layer of the cell, separating at donor-acceptor interfaces into free charge carriers (electrons and holes) that are collected as electrical current when they reach the cell electrodes.

In spite of the attractions of polymer solar cells, their large-scale application has been limited by the relatively low power-conversion efficiency, which is defined as the percentage of the power generated by the cell versus the power of the incident sunlight. The power produced by a solar cell is the product of three cell performance parameters: the open circuit voltage, the short circuit current and the fill factor. Various strategies now are being developed to increase these parameters to maximize the power-conversion efficiency of the cells.