ASU researchers reach 25.4% efficiency of tandem perovskite/silicon solar cells

Researchers from Arizona State University have achieved 25.4% efficiency in their tandem solar cell stacked with perovskite and silicon. This follows, and surpasses, last year's achievement of 23.6% efficiency.

The team's improvement upon the record by nearly two percentage points was reached in a joint project with researchers at the University of Nebraska'Lincoln, predicting they'll be nearing 30% tandem efficiency within two years.

'The cost of solar electricity is largely driven by the efficiency of the panels installed,' the team said. 'So, the increase in cell efficiency that we've demonstrated has the potential to lower the cost of solar energy, which will in turn mean that more solar panels will be installed.'

While spinning the precursor solution on top of a silicon cell, the additives increase the grain size of the perovskite, enhancing its photovoltaic characteristics and resulting in a higher open-circuit voltage of the perovskite/silicon tandem solar cell. In other words, it increases the maximum voltage that the solar cell outputs.

'Based on our previous 23.6% tandem with a voltage of only 1.65 volts, we saw a huge opportunity for higher voltage to get higher efficiency,' said the researchers. 'The 1.80 volts open-circuit voltage of the new tandem is the highest demonstrated, making it one of the most efficient perovskite/silicon tandem cells in the world.'

The team feels that perovskite/silicon tandem cells have the potential to transform mainstream silicon technology and support the U.S. Department of Energy's SunShot Initiative to cut the cost of solar-generated electricity by half between 2020 and 2030. At the cost target of $0.03 per kilowatt hour, solar electricity would be among the least expensive options for new power generation.

The interdisciplinary team of chemists, device physicists, electrical engineers and material scientists are now turning their attention to the other two solar cell parameters that determine efficiency ' short-circuit current and fill factor ' in an effort to exceed the maximum theoretical efficiency of a silicon solar cell.

'This is a big advancement of ASU's cutting-edge research on silicon-based tandem solar cells,' the team said. 'Once the efficiency gain is big enough to justify the add-on cost of the additional perovskite layer, we envision it would be first adopted by the residential and commercial markets, which have higher balance-of-system costs.'

The team envisions its tandem solar cells will be on roofs in approximately 10 years.

In support of this and related research, the research tea, was recently awarded $2.5 million from the Department of Energy's Solar Energy Technologies Office to develop characterization tools that will allow the team to pinpoint losses in perovskite solar cells and use a new deposition technique to minimize short-circuit current and fill factor losses to improve solar cell efficiency.