Researchers unlock new path for ultra low-cost solar by swapping out scarce and costly metal in PV cells

An international team of researchers has successfully built the first high-performance, commercial-scale tandem solar cell that does not rely on indium, a scarce and expensive metal, replacing it instead with a material that is far more abundant and costs one per cent as much.

One of the many challenges facing the clean energy industry is its frequent reliance upon rare earth materials that are, as the name suggests, scarce, therefore expensive, and often mined in morally dubious conditions, at best.

This is specifically the case for indium, which is extracted exclusively as a byproduct of processing base-metal ores such as zinc sulphide. Indium therefore only occurs in trace amounts and, despite its use in a wide range of electronics, its limited supply presents costly challenges for large-scale manufacturing.

In an effort to bypass these inherent inefficiencies, a group of international researchers from China, Australia, and the UK have successfully built a high-performance and commercially sized tandem solar cell that switches out indium-based oxide with tin oxide, without sacrificing performance.

The breakthrough creation, published in the journal Science, could bring next-generation tandem solar cells one step closer to commercial production, paving the way for cheaper solar panels that also generate more electricity from the same amount of sunlight.

Professor Yuan Cheng from Monash Suzhou in China and Monash University’s Department of Materials Science and Engineering said the milestone marks the first realisation of a large-area, highly efficient indium-free perovskite tandem solar cell, showing that the technology can be scaled beyond laboratory-sized devices.

“Considering the cost of tin is a mere one per cent of that of indium, this breakthrough unveils a new material paradigm and a highly viable engineering route for low-cost, sustainable, and scalable tandem photovoltaics,” said Professor Cheng.

“Ultimately, this work is of paramount strategic importance for propelling the industrialisation and terawatt-scale deployment of next-generation ultra-high-efficiency photovoltaic technologies.”

The research was carried out by at least 30 researchers from a range of institutions and companies, including Monash Suzhou, the College of Energy, Institute of Functional Nano and Soft Materials (FUNSOM), the Department of Materials at the University of Oxford, and the Department of Materials Science and Engineering at Monash University, Clayton.

The researchers were able to successfully replace indium with tin oxide using what they describe as a “low-damage reactive plasma deposition process” resulting in the creation of commercially sized solar cells with a certified efficiency of 31 per cent.

The solar cells were able to withstand heat, humidity, and more than three months of outdoor operation, all while still maintaining strong performance.

Professor Cheng also explained that achieving more than a 30 per cent efficiency in a commercially sized tandem module is in and of itself a major technical milestone, demonstrating that high performance can be maintained without relying on scarce and high-cost materials. 

“The research team developed a reactive plasma deposition (RPD) process for tin oxide (SnOx) films to serve as the recombination layer, achieving a remarkable certified efficiency of 33.6 per cent on 1 cm2,” Professor Cheng said.

“By further extending the application of RPD-SnOx to both the front and rear transparent electrodes, we successfully fabricated indium-free tandem solar cells.  Remarkably, we scaled this technology up to a 207.9 cm2 mini-module, obtaining an outstanding certified efficiency of 31.0 per cent.”

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