Third Generation Solar Cells: An Overview

 

Several new solar cell or photovoltaic technologies have been researched in the last few years, with respect to finding an effective alternative to silicon-based solar cells. Research and development in this area generally aims to provide higher efficiency and lower costs per watt of electricity generated. Some in the solar cell industry identify different "generations" of solar cell technology. The third generation is somewhat ambiguous in the technologies that it encompasses, though generally it tends to include, among others, nonsemiconductor technologies (including polymer-based cells and biomimetics), quantum dot technologies, tandem/multi-junction cells, hot-carrier cells, dye-sensitized solar cells and upconversion technologies.

Though the theoretical upper limit with regard to the conversion of sunlight to electricity is 33% for a standard solar cell, the Carnot limit is about 95% for the same. This opens the door for enhancing the efficiency of solar cells two to three times provided various concepts can be put into use for improving efficiency without bearing high costs. There is considerable research under way to develop low-cost semiconductor materials that could have its bandgap tuned for optimum performance permitting the control of the absorptive properties of the solar cell. This is what has been attempted in third generation solar cells--alternative materials to harness the solar energy.

Innovalight is one of the Bay Area-based Startups that have pioneered the development of silicon nanoink-based solar cells. Sources claim, lab efficiencies are as high as 36%.

Evident Technologies, based in Pennsylvania, is another company that develops quantum dot-based solar cells that are primarily targeted at applications such as calculators and signal lamps where the power output is less than 5 W. They have developed a product line comprising quantum dots that have been shoehorned for this nature of tunability providing the industry a ripe chance to develop market competitive PV solar cells. On a nanometer scale, the quantum dots utilize the quantum properties of materials, enabling them to assist in overcoming the limitations of the conventional semiconductor devices. These quantum dot semiconductors possess the novel ability to inexpensively capture copious quantities of sunlight, while at the same time retaining the versatility of form that quantum dots can be made into, such as flexible sheets or made to be transparent material. The considerably low-cost and excellent performance of quantum dots as compared with the conventional silicon semiconductor materials and thin films permits these dots to theoretically attain the goal of almost 60% efficiency and a cost of $100 or less for every square meter of paneling required to make PV solar cells economically competitive.

Organic semiconductor material-based solar cells have commercial efficiencies of less than 5% and are mainly used for much smaller applications. A prominent player in this area is Pennsylvania-based Plextronics that has been constantly innovating on this platform technology and has developed some prototypes that operate at 6% efficiency.

Another important player in this area has been NJ, USA-based Konarka Technologies that develops nanoplastic-based solar cells that are mainly used in smart fabrics and powering of laptops and other portable electronics devices.

Impact of Third Generation Solar Cells:

Traditional solar cells have had several major drawbacks that need to be worked upon to constantly overcome barriers for high performance. Low efficiency and high cost are the foremost factors that are needed to be overcome for a much more robust technology to be in place. Also, the key ingredient, refined silicon, has become more expensive, which makes it difficult to reduce the cost of the solar cells. Silicon also has many physical barriers, which limit the efficiency and use of traditional solar cells. Nanotechnologists and other University innovators are developing newer solar cells that are less expensive, flexible, compact, light weight, and efficient. They are able to do this by finding alternative chemicals and materials to harness solar energy. One such example is Innovalightís Silicon Nanoink Technology that exploits siliconís quantum effects to generate very high efficiencies in the solar cell (at 36%) on a lab scale. Some of the other examples of these materials include organic materials (polymers and conjugated polymers), quantum dots and plastics.

One of the fundamental actors going for organic materials is that they offer very high possibilities for improving parameters such as charge generation, separation, molecular mass, bandgap (determining the ability to harvest light efficiently in different parts of the solar spectrum, especially the infrared), molecular energy levels, rigidity, and molecule-to-molecule interactions. They are also extremely lightweight and flexible making them easy to work with and combine with other molecules.

Additionally, these organic materials are compatible with plastic and other flexible substrates; and devices can therefore be fabricated with low-cost, high throughput printing techniques that consume less energy and require less capital investment than silicon-based devices and other thin-film technologies. The reduction in cost is almost 30% to 40%. Despite all of these great advantages, organic solar cells suffer from very low efficiencies of just 5 % on an average and thus this has limited their use. This efficiency needs considerable improvement if these cells have to compete in the market place. Organic and plastic solar cells are the only two types of third generation solar cells that have hit some volumes for mass production. These production volumes, however, are not going to improve much until the demand for these cells goes up. These cells are still used only for smaller applications (those that require less than 10 W of power) and these production volumes will improve only if the demand from the big league (utilities, roof top applications) for these cells increases. That will not happen until higher efficiencies are reached.

Details:

Vijay Shankar Murthy

Industry Manager

Technical Insights

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