Researchers from King Abdullah University of Science and Technology (KAUST) have fabricated efficient, two-terminal monolithic perovskite-silicon tandem solar cells and tested them outdoors. The tandem device that resulted from this research was found to be more stable than conventional perovskite cells and, importantly, optimized for use in industry.

Perovskite/silicon cells under test at KAUST outdoor facility

The findings of KAUST Research Scientists Dr. Erkan Aydin and Dr. Thomas Allen, and colleagues in Professor Stefaan De Wolf's group, indicate that the temperature dependence of both the silicon and perovskite bandgaps'which follow opposing trends'shift the current-matching-optimization point away from that for two-terminal tandems under standard test conditions.

South Korea's Ministry of Trade, Industry and Energy (MOTIE) recently released a new roadmap for the domestic solar module industry that puts a strong focus on solar applications.

According to the document, domestic solar manufacturers and research institutes expect tandem solar cell technology based on silicon and perovskite to be the most promising candidates for PV products of the next generation. The Korean semiconductor and display industries, according to the MOTIE, may play a decisive role in this transition by providing its expertise in silicon product and thin film development.

The Institute for Solar Energy Research Hamelin (ISFH), the Karlsruhe Institute of Technology (KIT) and the Institute for Materials and Components in Electronics at the University of Hannover, as well as Centrotherm, Singulus, Meyer Burger and Von Ardenne, are involved in a research project aimed at achieving 33%-efficient perovskite-silicon tandem solar cell suitable for mass production.

The new research project is called '27plus6′ and it brings together the expertise of leading German and Swiss technology companies and research institutes. The consortium said that it aims to achieve the promised conversion efficiency under standard test conditions, and that is also seeking to reach a higher power yield, intended to accelerate industrial implementation.

Researchers at Cambridge's Department of Materials Science and Metallurgy, working with Imperial College London and the Solar Energy Research Institute of Singapore, have developed a method to print ultrathin coatings on perovskite-based solar cells, allowing them to work in tandem with silicon solar cells to boost efficiencies.

Solar cells work by absorbing sunlight to produce clean electricity. But photovoltaics can absorb only a fraction of the solar spectrum, which limits their efficiencies. The typical efficiency of a solar panel is only 18-20%.

Researchers at Arizona State University have demonstrated a perovskite-silicon tandem cell they claim has low reflectance losses and strong potential for commercial production. The ASU team says that this new cell could lead to 30% efficiency tandem devices. The tandem architecture involves a manufacturing process featuring the solution-based blading of perovskites onto textured silicon wafers.

Image credit: Joule

The device is manufactured in a nitrogen-assisted blading process which ensures deposition of the perovskite layer onto textured silicon is achieved with typical pyramid heights of 1μm. The manufacture of such tandem devices typically results in perovskite heights of 3-10μm.

Researchers from Helmhotlz-Zentrum Berlin (HZB), collaborating with teams from University of Cambridge, Eindhoven University of Technology, Nicolaus Copernicus University, Salerno University and others, have developed a monolithic "two-terminal" tandem cell made of CIGS and perovskite that achieved a certified efficiency of 24.16%, with a thickness of well below 5 micrometers - which would allow the production of flexible solar modules.

Tandem cells combine two different semiconductors that convert different parts of the light spectrum into electrical energy. Metal-halide perovskite compounds mainly use the visible parts of the spectrum, while CIGS semiconductors convert rather the infrared light. CIGS cells, which consist of copper, indium, gallium and selenium, can be deposited as thin-films with a total thickness of only 3 to 4 micrometers; the perovskite layers are even much thinner at 0.5 micrometers.

Researchers at The Australian National University (ANU) have announced an impressive achievement - a silicon/perovskite tandem solar cell with a conversion efficiency of 27.7%.

Professor Kylie Catchpole says this would only need to improve slightly - to around 30% - before the technology could be rolled out around the world. "In comparison, typical solar panels being installed on rooftops at the moment have an efficiency around 20%" Professor Catchpole said.

Scientists from Hasselt University, imec, VITO, EnergyVille and international partners within the PERCISTAND consortium have announced that they achieved an energy efficiency of 25% with a thin-film solar cell.

Bart Vermang, coordinator within the PERCISTAND consortium, describes the development of thin-film solar cells as 'Pioneering'. The consortium, which partly consists of the collaborations within EnergyVille and Solliance, has succeeded in achieving a record energy efficiency with thin film solar cells. 'We've achieved an energy efficiency of 25 percent for the first time, which is just as much energy as a traditional solar cell can generate on a day-to-day basis. And we haven't yet reached the upper limit of our thin-film solar cells.'

Scientists from Japan's Gifu University and the Tokyo Institute of Technology have identified a chalcogenide perovskite material with light absorption attributes strong enough to offer the potential for a theoretical maximum conversion efficiency of 38.7% in a silicon perovskite tandem solar cell.

The material ' BaZrTiS₃ ' has a light absorption coefficient exceeding 10⁵cm^-1, the highest of all solar cell materials including chalcogenide perovskites such as SrZrS₃, BaHfS₃ and SrHfS₃, the scientists claim.

The groups of Steve Albrecht and Bernd Stannowski at HZB have reached a record efficiency of 29.15% of its tandem solar cell made of perovskite and silicon.

The illustration shows the structure of the tandem solar cell: between the thin perovskite layer (black) and the silicon layer (blue) are functional intermediate layers. © Eike Köhnen/HZB

This value has been officially certified by the CalLab of the Fraunhofer Institute for Solar Energy Systems (ISE) and means that surpassing the 30% efficiency mark is now within reach.