Solar cells are categorized into three generations: first generation is high cost, high efficiency, second generation is low cost, low efficiency, and third generation is a research target with the goal of producing low cost and high efficiency cells.
There are three basic generations of solar cells, although one of them doesn’t exist yet and research is ongoing. They are designated as first, second and third and differ in their cost and efficiency.
The first generation is high cost, high efficiency. These solar cells are manufactured similar to computers, using extremely pure silicon, use a single junction to extract energy from photons, and are very efficient, approaching their maximum theoretical efficiency of 33%. In 2007, first generation products accounted for 89.6% of commercial production, though market share has declined since then. The manufacturing processes used to produce them are inherently expensive, meaning these cells could take years to pay off their purchase costs. It is not thought that first-generation cells will be able to provide energy more cost-effectively than fossil fuel sources.
The second generation, which underwent intense development in the 1990s and early 2000s, consists of low-cost, low-efficiency cells. These are most frequently thin-film solar cells, designs that use minimal materials, and cost-effective manufacturing processes. The most commonly used materials for this type are copper, indium and gallium selenide, cadmium telluride (CdTe), amorphous silicon and micromorphic silicon.
A standard example of second generation cells would be those made by Nanosolar, which uses a special machine to print cells at an extremely high speed. While these cells only have a conversion efficiency of 10-15%, the low cost more than makes up for this deficit. Second generation cells have the potential to be cheaper than fossil fuels.
Third-generation solar cells are just a research target and don’t exist yet. The goal of solar energy research is to produce cells with low cost and high efficiency. These are likely to be thin-film cells using novel approaches to achieve efficiencies in the 30-60% range. Some analysts predict that third generation cells could start to be commercialized around 2020, but this is only a hypothesis. Technologies associated with third generation products include multi-junction photovoltaic cells, tandem cells, nanostructured cells to better collect incident light, and use excess thermal generation to enhance voltages or carrier collection.
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