A silicon solar cell has a ceiling it cannot pass. Silicon absorbs some wavelengths of sunlight well and wastes others, and the physics of that mismatch caps a single-junction silicon cell at around 29% conversion efficiency. Commercial panels sit several points below it. The industry has spent decades closing on a limit it cannot break.

The way past it is to stop using one material. A tandem cell stacks a second layer on top of the silicon, tuned to capture the wavelengths silicon handles badly. Perovskite is the material of choice for that top layer, because its absorption can be tuned by changing its chemistry, and because it can be deposited at a low temperature onto a finished silicon cell.

ART-PV India is building them. Formally Advanced Renewable Tandem-Photovoltaics India, it is incubated at IIT Bombay and grew out of the National Centre for Photovoltaic Research and Education there, with Professor Dinesh Kabra leading the work.

Two cells, one device

The company has reported a two-terminal monolithic tandem cell reaching 29.8% conversion efficiency, combining silicon and CdTe with perovskite. Both of those technical words matter. Monolithic means the layers are grown as a single device rather than assembled from two separate cells. Two-terminal means it has the same two electrical connections as an ordinary panel, so it can drop into existing systems.

That figure is a laboratory cell measurement, and full-sized modules always test lower than individual cells. It is also a research result rather than a product specification, though it sits above what any single-junction silicon cell can achieve, which is the point of the architecture.

Compatibility with both major panel technologies is the company's commercial argument. Its top layer can go onto crystalline silicon, which dominates the world market, or onto cadmium telluride thin film, which is the main alternative.

That is reflected in who is backing it. First Solar, the American manufacturer that runs a thin-film plant near Chennai, and Waaree, India's largest crystalline silicon manufacturer, are both partners, and the company says they hold preferential licensing rights in exchange for helping develop and commercialise the technology.

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Ten million dollars, and a line on campus

The Ministry of New and Renewable Energy is funding a pilot manufacturing facility of about $10 million on the IIT Bombay campus, intended to produce commercial tandem cells rather than laboratory samples. ART-PV India has access to a cleanroom of around 5,000 square feet in the institute's research park, with fabrication, characterisation and simulation equipment.

The institutional depth behind it is unusual. The National Centre for Photovoltaic Research and Education was set up at IIT Bombay in 2010 with ministry funding, and has received over Rs 200 crore across fifteen years. A company emerging from it starts with equipment and expertise that a startup would otherwise spend a decade acquiring.

The endorsement has been political as well as financial. During a visit to the centre, Pralhad Joshi, the Union Minister for New and Renewable Energy, described the cell as a national milestone and among the highest performance levels achieved in India, and said the pilot facility was intended to keep the intellectual property domestic.

What has not been published is a production timeline, a module-level efficiency figure, a durability result or a commercial product. Perovskite's central unsolved problem is that it degrades under heat, moisture and ultraviolet light, and a tandem cell inherits that weakness from its top layer.

(This story has been researched and compiled using publicly available information.)