Metal replacement creates low-cost tandem solar cells

An international team of researchers has built a tandem solar cell that doesn’t rely on the scarce and expensive metal indium.

The research breakthrough replaces indium-based oxide with abundant tin oxide, a material that costs 1% of the cost of indium, without sacrificing performance.

The researchers said the study will bring next-generation tandem solar cells a step closer to commercial production, potentially creating cheaper solar panels that generate more electricity from the same amount of sunlight.

Professor Yuan Cheng from Monash Suzhou and the Department of Materials Science and Engineering at Monash 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 1% 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,” Cheng said.

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

As demand for solar energy continues to grow, reducing reliance on scarce materials is becoming increasingly important. Indium is used in a wide range of electronics, and its limited supply presents challenges for large-scale manufacturing.

By replacing indium with tin oxide using a low-damage reactive plasma deposition process, the researchers created solar cells that achieved a certified efficiency of 31% in a commercially sized mini-module while also improving durability.

The devices also withstood heat, humidity and more than three months of outdoor operation while maintaining strong performance.

Cheng said achieving more than 30% efficiency in a commercially sized tandem module is a major technical milestone, and demonstrates that high performance can be maintained without relying on scarce, 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% on 1 cm²,” 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%.”

The research paper has been published in Science.

Image caption: The research team’s commercially sized indium-free tandem solar cell, which achieved a certified efficiency of 31% using abundant tin oxide in place of scarce indium. Credit: Monash University