Coal India and IIT Bombay Patent Bifacial Perovskite Solar Cell That Captures Light From Both Sides

Coal India has announced the grant of a patent for a Bifacial Perovskite Solar Cell developed through its R&D collaboration with IIT Bombay. The technology is designed to harvest light from both the front and rear surfaces, while its perovskite thin-film architecture offers tunable bandgaps, flexibility and potential compatibility with tandem solar cells. Coal India’s R&D programme lists IIT Bombay as the principal implementing agency for the bifacial perovskite module project.

India’s solar industry has spent years trying to solve a deceptively simple problem: how can a solar cell make better use of the light that reaches it without making the technology dramatically more expensive or difficult to manufacture?

A research collaboration involving Coal India and IIT Bombay is exploring one answer by moving beyond conventional one-sided solar harvesting.

The newly patented Bifacial Perovskite Solar Cell is designed to capture sunlight from both its front and rear surfaces. Coal India says the technology can potentially increase energy generation from the same installation area while also offering characteristics that are attractive for next-generation tandem and thin-film photovoltaic systems.

A Solar Cell That Looks at Light From Both Directions

Conventional solar cells are generally optimized to receive sunlight from one primary direction. Bifacial photovoltaic technology changes that architecture by allowing the rear side of the device to contribute to electricity generation as well.

The idea becomes particularly interesting when applied to perovskite materials.

Perovskites are a class of semiconductor materials that have attracted enormous attention in solar research because they can absorb sunlight efficiently and can be processed into thin films. IIT Bombay’s National Centre for Photovoltaic Research and Education has been developing perovskite and perovskite-silicon tandem technologies, including work aimed at improving efficiency, manufacturing and stability.

Coal India’s own R&D programme identifies the project as “Prototyping of Bi-facial Perovskite Module Leading to 4-T Perovskite-Si Tandem Structure,” with IIT Bombay listed as the principal implementing agency.

Why the Rear Surface Matters

The rear side of a solar module does not necessarily receive the same intensity of direct sunlight as the front. But it can receive reflected and scattered light from the surrounding environment.

That additional illumination can become useful energy rather than simply being lost.

Coal India’s description of the patented technology highlights dual-side light harvesting and the possibility of higher energy yield from the same area. It also points to performance under diffuse and low-light conditions as a potential advantage.

This does not mean that a bifacial cell automatically produces twice as much electricity. Actual energy gain depends on factors such as installation geometry, surface reflectivity, shading, angle of incidence and the amount of light reaching the rear surface.

The value of the architecture is that it gives researchers another route to extract useful energy from photons arriving at the device.

The Bigger Opportunity Is Tandem Solar

One of the most important aspects of the Coal India-IIT Bombay project is its connection to tandem solar cells.

A conventional silicon solar cell has limits in how efficiently it can use the solar spectrum. Tandem architectures attempt to overcome some of those limitations by combining materials with different light-absorption characteristics.

Perovskites are particularly attractive as a top layer because their optical properties can be tuned by modifying their composition.

IIT Bombay’s NCPRE says its research programme is focused on silicon-perovskite tandem devices and has targeted efficiencies above 25% at the cell/module scale in its development work.

The Coal India project specifically targets a 4-terminal perovskite-silicon tandem structure, with earlier project documentation setting targets of approximately 20% module efficiency and 24% cell efficiency for the bifacial perovskite module, followed by higher projected performance for the tandem architecture.

Tunable Bandgap Could Give Perovskites an Important Role

The term bandgap describes the energy difference that determines which portions of the electromagnetic spectrum a semiconductor can efficiently absorb.

One of the attractions of perovskites is that their bandgap can be tuned through material composition.

That makes them particularly useful for tandem architectures, where different semiconductor layers can be designed to absorb different portions of sunlight.

Coal India says the patented bifacial perovskite technology has a tunable bandgap and could therefore be useful in high-efficiency tandem solar cells.

The concept is important because a tandem device does not simply try to make one material perform better at everything. Instead, it attempts to make multiple materials work together, with each layer handling a different part of the solar spectrum.

Thin Films Could Change Where Solar Cells Can Be Used

Another potential advantage is the physical form of perovskite technology.

Unlike conventional crystalline silicon wafers, perovskite solar devices can be fabricated as thin films. IIT Bombay’s research programme notes the potential of perovskite materials for low-cost processing, while its research on thin-film devices includes flexible and other emerging photovoltaic applications.

Coal India describes the patented bifacial technology as lightweight and flexible, with thin-film manufacturing offering possibilities for versatile applications. It also identifies potentially lower-cost manufacturing through low-temperature and scalable processes.

That could eventually broaden the range of surfaces where photovoltaic technology can be integrated.

Instead of thinking only about rigid panels mounted on rooftops or large solar farms, thin-film photovoltaics can potentially be considered for lightweight structures, building-integrated applications and other surfaces where conventional modules are less convenient.

From Coal Research to New Energy Technologies

The project also reflects a broader transformation underway inside India’s energy research ecosystem.

Coal India remains one of the country’s major coal producers, but its R&D activities increasingly include technologies related to alternative energy and sustainability.

Its research portal currently lists more than 18 ongoing projects and more than 40 partner institutions. Among those projects are perovskite solar technologies, carbon-electrode-based low-cost perovskite cells and the bifacial perovskite module project with IIT Bombay.

Coal India’s annual reporting has also documented its collaboration with IIT Bombay on indigenous perovskite module manufacturing and bifacial perovskite technology.

The significance is therefore larger than a single patent. It represents an effort to use established industrial R&D infrastructure to support technologies that could become part of India’s future energy mix.

The Technology Still Has to Cross the Commercialization Gap

A patent is an important intellectual-property milestone, but it is not the same as a commercially deployed solar product.

Perovskite photovoltaics still face challenges involving long-term stability, environmental exposure, manufacturing consistency and large-area scaling.

IIT Bombay itself identifies stability as a major issue for some perovskite technologies. Its research has therefore focused not only on efficiency but also on protective layers, more stable materials and tandem configurations.

The Coal India project documents indicate that the bifacial module work was intended to reach prototype-level development, while the broader tandem objective involves further technical development.

That means the next important stage will be demonstrating that the technology can maintain its performance outside the laboratory and eventually be manufactured reliably at useful scale.

India Is Building Its Own Perovskite Technology Pipeline

IIT Bombay is already expanding its infrastructure around next-generation photovoltaics. In July 2026, its NCPRE team moved into a new 6,300-square-foot cleanroom facility at the IIT Bombay Research Park focused on perovskite-silicon solar-cell development.

The institute has also reported laboratory-scale perovskite-silicon tandem achievements and collaborations with industry to strengthen equipment and characterization capabilities.

Together, these developments point toward an emerging domestic ecosystem covering materials research, device fabrication, testing, tandem architectures and eventual technology transfer.

The new bifacial perovskite patent adds another piece to that effort.

If researchers can combine dual-sided light harvesting with tunable perovskite bandgaps, thin-film manufacturing and silicon tandem architectures, the technology could offer a new pathway toward higher-output photovoltaic systems using less conventional material architecture.

For now, the patent marks a research and intellectual-property milestone rather than a finished commercial solar panel. But it demonstrates how Indian institutions are attempting to develop the underlying technologies that could define the next generation of solar power.