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The emerging technology that will allow skyscrapers to generate their own power has taken another step forward, with researchers in Australia increasing the energy efficiency and stability of ‘solar windows’ while allowing more visible light to pass through.

Semi-transparent solar cells that can replace window glass and become power generators have been advancing rapidly in recent years, raising the exciting prospect of many buildings – particularly those with glass facades – becoming close to self-powering.

In 2020, members of the ARC Centre of Excellence in Exciton Science created a solar window prototype that allowed 10% of visible light to pass through it, while achieving 17% power-conversion efficiency.

That’s close to the 20% power-conversion efficiency of normal rooftop silicon solar cells, which are not transparent and can’t be used as windows.

This research is focused on solar cells made from perovskite materials. They can be readily created in a laboratory and tuned to suit different purposes, including the type of energy they conduct and how much light they absorb, reflect and transmit.

The same team, based at Monash University and Australia’s national science agency CSIRO, have now demonstrated power conversion efficiencies of 15.5% and 4.1% for different types of prototype semi-transparent solar cells, with visible transmittance of 20.7% and 52.4% respectively.

While the power-conversion efficiencies are lower than their previous results, the amount of visible light these new materials allow to pass through is significantly greater, increasing their potential to be used in a wide range of real-world applications.

The researchers found that a combination of caesium and formamidinium in the initial perovskite composition delivered the best performance over different band gaps.

In solar cells, the band gap is the minimum energy that is harnessed for delivering power from the sun.

Significantly, these caesium and formamidinium perovskite solar cells demonstrated excellent long-term stability when tested for continuous illumination and heating, which mimics the conditions the devices would encounter in real-world use.

The project leader, Professor Jacek Jasieniak from the Department of Materials Science & Engineering at Monash University said: “This work provides a major step forward towards realizing high efficiency and stable perovskite devices that can be deployed as solar windows to fulfill what is a largely untapped market opportunity.”

The work was mainly funded through the Australian Renewable Energy Agency (ARENA). The results have been published in the journal Advanced Science and are available here.