New record on solar cell efficiency – 39.5% – built on quantum wells – pv magazine USA

May 23, 2022John Fitzgerald Weaver

The National Department of Energy’s Renewable Energy Laboratory (NREL) has set a new record for the efficiency of solar cells under conventional sunlight at 39.5%. The three-transition solar cell was able to set this record by improving the middle layer of the cell using new methods of constructing quantum wells.

NREL’s High Efficiency Crystal Photovoltaic (PV) Group has made a solar cell out of hundreds of layers of materialseach optimized based on previous iterations of solar cell technology over decades of research and development of this class of products.

The solar cell consists of three different materials: the upper compound is made of gallium-indium phosphide (GaInP), the middle layer – of gallium arsenide (GaAs), which is surrounded by the aforementioned quantum wells, and the lower – of the lattice. inappropriate gallium-indium arsenide (GaInAs). These materials have previously been used in solar cells and dominate the space solar energy market.

The previous record for standard solar cells was 39.2%, and although it was almost as effective as this new record, this cell was a six-unit unit. This solar cell, using similar materials, was able to increase the efficiency of generation, taking advantage of advanced research in the layers of quantum wells.

The authors noted that hundreds of layers of quantum wells are located between the central layer and the materials above and below it. These wells change the way electrons fed by photons are captured and moved through a solar cell into a chain of solar cells. During the experiment, the number of quantum wells ranged from 100 to 300 to obtain specific current characteristics depending on the voltage sought by the researchers. Quantum wells are five to ten nanometers thick, which has increased the total thickness of the middle layer – GaAs – from 850 nm to 2.5 mm, respectively.

The main problem with this class of products is that it is very expensive, at $ 10 per watt, compared to 10 cents for standard solar cells, and production is relatively slow compared to standard polysilicon solar panels. Also, given the inevitable future of global solar dominationthe availability of materials is limited.

For example, the growth time of the solar cell quantum well region was 55 minutes, and the total growth time of the common cell was four hours. And while this isn’t exactly a fair comparison, a standard 250MW / year polysilicon-based production line tends to move tens of thousands of solar cells per hour.

The high cost means that these cells are used mainly in expensive markets. The most common market is space, as the International Space Station uses triple cells with efficiencies of more than 30%. Cells of this style were also used in not yet released solar-powered cars.

Without a doubt, these are some of the most efficient solar panels ever developed, as seen in the expression above the famous NREL Research Cell Record Performance Diagram. The delineated red field is the current record for the efficiency of solar cells. The class of solar cells located above and to the left of the delineated cell set their records using concentrated sunlight through mirrors and other methods.

У previous research, the researchers noted that a theoretical efficiency of 85% is possible for an infinite number of transitions at maximum sunlight concentrations. However, using various reasonable assumptions, conservative calculations show that a 62% efficiency of solar cells can be achieved using sunlight that is concentrated 1000 times.