Thin as a wafer: the quest for the world’s most powerful, ultrathin and bendable silicon solar cell

New research led by a team of Chinese scientists has achieved the thinnest silicon solar cells ever – a flexible, paper-like material that converts light into electricity without sacrificing efficiency.

Silicon solar cells are the backbone of the world’s solar-generated electricity, accounting for about 95 per cent of the solar cells in the photovoltaic market. As manufacturing and power generation costs have declined, solar cells have gained wider use in ground-mounted solar farms and distributed photovoltaics.

State-run Science and Technology Daily quoted Li Yang, a professor at Jiangsu University of Science and Technology (JUST), on Monday as saying that crystalline silicon solar cells, which are made from silicon wafers, were the most mature and widely used photovoltaic power generation technology, “but they face two major technological bottlenecks”.

One drawback is that the power conversion efficiency of large-area silicon cells remains limited to 26 per cent; the other hindrance is cell thickness – typically 150 to 180 micrometres (0.15mm to 0.18mm), making it difficult for use in applications that require a more flexible and lightweight material, such as curved roofs, satellites and space stations.

Aircraft, for instance, have extremely stringent weight requirements and have used thin-film solar cells, another broad category of solar cells. However, according to Li, they are expensive, have a short lifespan, and are not well suited to commercial requirements.

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The flexible silicon solar cells developed by Li and his collaborators are much thinner and lighter than their conventional counterparts, and boast high power efficiency.

“We have developed crystalline silicon cells that are as thin as 50 micrometres – thinner than an A4 sheet of paper – that can be bent into a roll, and are much more efficient than conventional ones,” he said.

The research, published in the journal Nature on January 31, was a joint effort by scientists from JUST, Xian-based company LONGi Green Energy Technology, and Australia’s Curtin University.

Crystalline silicon solar cells are known as a “sandwich” structure, meaning their wafer substrate – the middle layer – accounts for more than 99 per cent of the cell’s thickness.

Scientists around the world have been using various approaches to develop solar cells that are lighter, more flexible, highly efficient and commercially viable.

In May last year, a group of scientists from the Shanghai Institute of Microsystem and Information Technology, Changsha University of Science and Technology, and the computer, electrical and mathematical science and engineering division at King Abdullah University of Science and Technology, reported that they had developed silicon solar cells that were just 60 micrometres thick, which could be folded like a sheet of paper.

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But the Chinese-led team has taken thinness even further. “Wafer thinning not only reduces the weight and cost [of solar cells], but also facilitates charge migration and separation,” the Nature paper said.

Still, achieving ever thinner wafers has typically come at the cost of efficiency – thinner silicon solar cells have typically been less efficient at converting sunlight into electricity than thicker ones.

In a briefing article published in the same issue, the authors said that previous thin crystalline silicon cells – less than 150 micrometres thick, produced using conventional techniques – had power conversion efficiencies (PCE) that ranged from 23.27 to 24.7 per cent.

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In this study, however, the scientists produced five types of thin cells ranging from 55 to 130 micrometres in thickness that all had a PCE greater than 26 per cent.

These ultrathin solar cells are also bendable. “While it cannot be folded in half, it can be bent into any curvature,” Li said, adding that the feature would greatly expand the range of applications for crystalline silicon cells.

Solar cells that are flexible have far more application possibilities, including uses in aerospace, blimps, drones and wearable smart devices.

Li said the researchers were working to develop more flexible and efficient crystalline silicon cells that could one day be as portable as a roll of film.

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