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Double-layered solar cell boasts record efficiency for energy capture

A double-layered solar cell developed by materials scientists from the UCLA Samueli School of Engineering has been shown to produce more energy than traditional panels.

The device is made by spraying a thin layer of perovskite - an inexpensive compound of lead and iodine that has been shown to be very efficient at capturing energy from sunlight - onto a commercially available solar cell.

The solar cell that forms the bottom layer of the device is made of a compound of copper, indium, gallium and selenide (CIGS).

The team’s new cell converts 22.4 per cent of the incoming energy from the sun, a record in power conversion efficiency for a perovskite-CIGS tandem solar cell.

The performance was confirmed in independent tests at the US Department of Energy’s National Renewable Energy Laboratory. The previous record, set in 2015 by a group at IBM’s Thomas J. Watson Research Center, was 10.9 per cent.

The UCLA device’s efficiency rate is similar to that of the polysilicon solar cells that currently dominate the photovoltaics market.

“With our tandem solar cell design, we’re drawing energy from two distinct parts of the solar spectrum over the same device area,” said materials science professor Yang Yan. “This increases the amount of energy generated from sunlight compared to the CIGS layer alone.”

Yang added that the technique of spraying on a layer of perovskite could be easily and inexpensively incorporated into existing solar-cell manufacturing processes.

The cell’s CIGS base layer, which is about 2 microns (or two-thousandths of a millimeter) thick, absorbs sunlight and generates energy at a rate of 18.7 per cent efficiency on its own, but adding the 1 micron-thick perovskite layer improves its efficiency - much like how adding a turbocharger to a car engine can improve its performance.

The two layers are joined by a nanoscale interface that the UCLA researchers designed; the interface helps give the device higher voltage, which increases the amount of power it can export.

The entire assembly (pictured above) sits on a glass substrate approximately 2mm thick.

“Our technology boosted the existing CIGS solar cell performance by nearly 20 per cent from its original performance,” Yang said. “That means a 20 per cent reduction in energy costs.”

He added that devices using the two-layer design could eventually approach 30 per cent power conversion efficiency. That will be the research group’s next goal.

In March, a team of Chinese researchers demonstrated a method which enables solar cells to generate electricity from the falling of raindrops, improving their efficiency and allowing them to generate energy even at night. 

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