Silicon Versus Polymer-Based Solar Cells

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The development of photovoltaics (PV) can be traced back to the 1950`s, first involving the use of organic dyes and their photoconductivity properties. Later, in the early 1980`s polymers were introduced in simple PV cells.  By then the challenge was to increase the Power Conversion Efficiency (PCE) from a stunted 0.1%.

A major breakthrough came in 1986 when the concept of heterojunction came into play (a donor and an acceptor together in one cell) increasing the PCE to 1%. Since then, earlier problems in obtaining efficient charge carrier separation have been overcome and PCE of more than 3% have been reported with the creation of the so-called double-cable polymer.

The improved PCE of plastic solar cells combined with increased (shelf and operating) lifetime, superior material properties and available manufacturing techniques anticipated plastic PVs arrival to the marketplace a few years after. Currently, the main component of most PV modules is silicon.  Thin film silicon reduces the volume of material needed by spraying a thin layer of silicon on to a surface, so has the potential to reduce impacts and waste.

In the lab, Polymer Solar Cell (PSC) efficiency reaches about 13 percent, which is far from the 20 percent efficiency of commercial solar panels. PSCs that use P3HT: PCBM polymers, introduced in 2002, are the standard “workhorse” design and yield about 3.5 percent efficiency. Recent advances in chemistry, geometry, and the development of tandem solar cells that stack multiple layers together have made this greater efficiency possible.

Advantages vs Disadvantages of PSC

On the other hand, in spite disadvantages of organic polymer solar cells (PSCs), such as low efficiency, low stability, and low strength, they show potential to provide solar power to remote microwatt sensors, wearable technology, and the Wi-Fi-connected appliances. PSCs use organic polymers to absorb light and convert it into electricity. While PSCs cannot match the durability or efficiency of inorganic solar cells, the potential to mass-produce nontoxic, disposable solar panels using roll-to-roll production makes them attractive for additional applications.

In the Journal of Renewable and Sustainable Energy from AIP Publishing, Paul Berger and Minjae Kim of Ohio State University make an assessment of PSc `s current technology in a paper published earlier this year.

In spite the increasing growth of PSC research in the last two decades, and the associated publications and patents, it seems improbable that this technology will unfold to replace inorganic solar cells.  Instead, Berger sees PSCs as complementary. They can bypass the high-voltage transmission lines and provide electricity to point-of-use devices that would otherwise require toxic batteries. He adds “PSCs have this ability to be flexible because they basically are plastics so you can put them on backpacks, jackets and even coffee creamer, a whole range of things where it’s at the point of use, it’s a disruptive business model.”

The polymers can be dissolved in solvents and printed onto a flexible backing using affordable roll-to-roll production, making this technology especially attractive. “This printing press is not unlike the one for printing your Sunday newspaper, but instead of three primary colors and black, you’re printing the four or five different layers needed for the solar cell, diodes, and transistors,” Berger said. Long rolls of solar cells also open up new applications, such as wrapping vehicles or covering building facades and windows.

Limited Applicability

Among the issues potentially limiting PSC applicability stand: a) Short-term replacement of costly materials, such as indium tin oxide and fullerenes, involved in heterojunction, b) Longevity as a related issue due to the polymers and reactive metal cathodes oxidizing when exposed to water and oxygen making it necessary to encapsulate the solar cells for protection. This encapsulation can be very effective on glass but is more challenging on flexible surfaces, like potato chip bags.

A handful of companies in the U.S. and Europe are working to bring viable PSCs to market. If successful, then PSCs could establish their own niche apart from silicon solar cells, powering all manner of remote devices.

[via eurekalert]