BIG LEAP: India took eight years to install 20GW solar generation capacity, but set up 100 GW in the next eight | Photo Credit: DHIRAJ SINGH

Vinay Rustagi, Chief Business Officer at Premier Energies Ltd, a solar cell and module manufacturer, believes that in just three to four years, the market will see solar cells with conversion efficiencies above 30 per cent, compared with about 25 per cent today. That would be a huge leap. The efficiency here indicates how much of the sunlight falling on the solar cell is converted into electrical energy.

High-efficiency cells are the next frontier of the solar industry. In India, the sector has come a long way since its beginnings in 2010, when the National Solar Mission was launched.

It took the industry eight years to set up 20 GW of manufacturing capacity; in the next eight, it added 100 GW. This was possible mainly because China hammered down module prices — modules account for 55–60 per cent of the cost of a solar plant. But cost efficiency arising from improvements in cell efficiency (cells are assembled into modules) also played a significant role.

Cell efficiency has increased from around 17 per cent to 25 per cent over the last decade. Rustagi expects a repeat of that trajectory. “There is rapid progress. I am pretty optimistic that by 2028 or 2029, there will be commercially available tandem solar cells with efficiencies above 30 per cent,” he told businessline.

A one percentage point increase in module efficiency can mean an additional 13,000–17,000 kWh of generation per MW of installed capacity annually. At a tariff of roughly ₹3 per kWh, this translates to ₹40–50 lakh worth of additional generation for a 100 MW plant. A five percentage point gain, therefore, works out to be ₹2–2.5 crore worth of extra generation.

Scientists broadly agree with Rustagi. Research literature is replete with reports of high-efficiency cell development. For instance, Prof Dinesh Kabra, who has founded the startup ART-PV India, has developed a tandem cell boasting 30.2 per cent efficiency. ART-PV is setting up two manufacturing plants in Mumbai, and Kabra expects the cells to reach the market within two years.

Bandgap engineering

Behind the improvements in cell efficiency lies a science called bandgap engineering.

Light consists of streaming photons of multiple frequencies (and corresponding wavelengths). Each colour of light occupies a different frequency band; even within a single colour, there are multiple frequencies.

Photons of different frequencies carry different amounts of energy — even though they all travel at the same speed. Think of it as two cars moving at the same speed, one carrying a single passenger and the other four.

In a semiconducting material such as a solar cell, a photon transfers its energy to an electron, allowing the electron to move from the valence band to the conduction band. The energy difference between these two bands is called the bandgap.

If the bandgap is too large, many photons do not have enough energy to excite electrons, resulting in lost sunlight energy. A single-junction solar cell has a fixed bandgap, and the well-known Shockley–Queisser limit states that its efficiency cannot exceed 33 per cent. Beyond a point, improving solar-cell efficiency becomes a material and device architecture problem.

A tandem cell addresses this by stacking two layers — like two slices of bread — each with a different bandgap. The top layer absorbs some photons, the bottom layer absorbs others, allowing more of the solar spectrum to be used to raise the overall efficiency.

Globally, scientists are working furiously on bandgap engineering. For example, Sarowr Basm Almahsen and Ghaleb Ali Al-Dahash of the College of Science for Women, University of Babylon, in Hilla (Iraq), have developed a tandem cell, combining two materials. In a paper published in Results in Optics, they write: “We suggest a solar cell made entirely without lead, using two layers: a top layer made of Cs₂AgBi₀.₇₅Sb₀.₂₅Br₆ [cesium silver bismuth-antimony bromide] with a wide bandgap of 1.8 eV, and a bottom layer made of FASnI₃ [formamidinium tin triiodide] with a narrow bandgap of 1.41 eV. This is a critical advancement, as most high-efficiency tandem cells still rely on toxic lead-based perovskites (e.g., MAPbI₃ [methylammonium lead iodide]).”

A bandgap difference of 0.39 eV is quite significant in semiconductor physics. The researchers claim a cell efficiency of 28.2 per cent.

In another paper, a team of scientists from various Indian universities report a tandem cell that places a perovskite layer on top of a conventional CIGS (copper indium gallium selenide) cell, creating a bandgap difference of 0.53 eV. The claimed efficiency is 32.56 per cent.

Switching to tandem

All this physics is fascinating — but how does a company that has invested millions of dollars in conventional cell manufacturing make the leap to tandem cells?

Rustagi says it is possible to retrofit an existing plant. Premier Energies is investing ₹5,000 crore to expand its cell and module capacities to 10.6 GW and 11.1 GW, respectively, by September 2026. Rustagi is not worried about the transition. “We are building a flexible design into our plants to make sure that we can retrofit them easily and make them compatible with these new technologies,” he says.

Kabra believes silicon–perovskite tandem cells will certainly enter the market before 2030. “If India does not move fast, once again the Indian market will be flooded with Chinese products,” he cautions.

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Published on January 12, 2026