Quantum wells allow record-efficiency two-junction solar cell

• Scientists from the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) and also the University of New South Wales attained a new world-record performance for two-junction solar cells, producing a cell with two light-absorbing layers that transforms 32.9% of sunshine into electrical power.

Trick to the cell's style is a series of more than 150 ultrathin layers of alternating semiconductors that produce quantum wells in the cell's lower absorber, permitting it to catch power from a key series of the solar spectrum. While the brand-new record only enhances modestly on the previous 32.8% effectiveness record, it is the first record-efficiency multijunction solar cell to make use of a strain-balanced structure-- a style that holds guarantee for more renovations.

The new cell is explained in an article in Advanced Energy Materials titled "High Efficiency Inverted GaAs and GaInP/GaAs Solar Cells With Strain-Balanced GaInAs/GaAsP Quantum Wells." The cells have a gallium indium phosphide (GaInP) layer for their top junction and a lower junction of gallium arsenide (GaAs) striated with 80 piled layers of quantum wells. A quantum well is produced when a slim layer of semiconductor product is sandwiched between 2 layers of product with a broader bandgap, confining charge service providers to the main layer.

Quantum Wells Offer Possibilities

The addition of a lot of quantum wells in the bottom junction reduces that junction's reliable bandgap, enhancing the wavelength of light it can absorb. Catching longer wavelengths enables the tandem cell to catch even more power from the solar spectrum, making the cell much more effective at transforming light to electrical power.

Traditionally, quantum wells have mostly been utilized in lasers, LEDs, as well as electronic devices for telecoms. As part of the advancement process, the NREL team generated a single-junction cell that demonstrated a really high outside radiative efficiency (> 40%)-- the effectiveness with which the cell converts electrical energy to light when run in reverse. While the group was not trying to develop an LED gadget, their high-quality quantum wells showed some potential around, too.

Stress Balancing Unlocks New Record

Previous work has attempted to use quantum wells to adjust the bandgap of solar cell junctions, yet it has actually not produced any kind of record-efficiency cells, partially since it is difficult to expand many, numerous layers of top quality quantum well product. If the layers end up being too thick or the mechanical strain within the crystal latticework is not effectively stabilized, the cell develops problems.

For their world-record cell, the team alternated layers of gallium indium arsenide-- in compression-- as well as gallium arsenide phosphide-- under tension. By carefully managing the thickness of these layers, the stress of the compressive and tensile pressures equilibriums between layers. A variety of lasers was used to gauge the curvature of the wafer throughout the development process, permitting the scientists to find as well as adjust for stress in the crystal latticework.

" This work will result in higher-efficiency solar cells for one-sun applications, which could be a significant driver of the prevalent fostering of these cells," said Myles Steiner, an elderly researcher on the NREL team. "Now, a crucial difficulty in advance is to discover exactly how to produce these cells in a cost-competitive manner."

Globe-Spanning Collaboration Yields Results

The growth of this cell style outgrew a close cooperation between part of the High-Efficiency Crystalline Photovoltaics study group at NREL and a team at the University of New South Wales (UNSW). Actually, Steiner spent 3 months in very early 2020 in New South Wales with his Australian collaborators, servicing the project as part of a grant from the Fulbright Scholars Program.

" Our collaboration combined NREL's lengthy standing know-how in epitaxial growth and UNSW's operate in solar cell modeling, which aided us to collaborate efficiently at a distance," said Nicholas Ekins-Daukes, that led the UNSW team. "I was excited with how quickly we were able to develop the initial composite, strain-balanced semiconductor product to surpass a conventional solar cell."