Sticky Power – New Peel and Stick Solar Cells Could Give TFSCs a New Lease of Life
The solar panel has always been the undisputed icon of clean, limitless energy. However, though they have been around since the 1950s, their adoption has been hindered by technological and cost barriers.
Most solar panels you see on rooftops and solar power stations are made from crystalline silicon (c-Si), which is expensive to procure and work with.
They are also very rigid in construction, which limits their installation to flat surfaces only.
(Howwegettonext.com / Pinterest)
To get around this problem, researchers in the 1970s began experimenting with other substances which demonstrated photovoltaic properties -- amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) showed promise. Solar cells made from any of these can be adapted to stick to a variety of different flexible substrates allowing them to be transported, and installed with greater ease.
The first TFSCs or thin film solar cells thus rolled out, and their adoption has been steadily increasing. Today, thin film solar cell represents 10% of the global solar power market.
One of the bigger advantages TFSCs offer over conventional solar cells is that they are about 30% cheaper, mainly due to the ease with which they can be installed. By 2009, TFSCs had won a respectable 18% of the market and it looked like they were well on their way to seeing widespread usage.
However, this was before cheaper c-Si solar panels from manufacturers in China began making inroads into the solar power market. Despite their higher price tag, traditional silicon-based solar cells still offer efficiencies much superior to what TFSCs can (commercially) provide. As Chinese manufacturers ramped up production, the cost of solar panels declined rapidly, making them a very attractive option for commercial and residential usage alike.
By 2012, the share of TFSC had slumped to 11%, and many manufacturers ended up declaring bankruptcy. In fact, the global market share of TFSC is expected to fall to 7% by 2017.
Innovative new peel and stick TFSCs promise a brighter future
This situation might change if a new type of sticker like TFSC developed by a team of enterprising researchers at Stanford University, US and Hanyang University, China finds its way to the manufacturing lines.
Led by Xiaolin Zheng at Stanford, and Professor Dong Rip Kim at Hanyang, the teams announced they had developed a way to create TFSCs which could be stuck to virtually any flexible surface. These cells not only have the potential to bring down the cost of manufacturing and installation even further, but open up a whole new way of using solar cells.
Imagine solar cells stuck to a window in your home, which can be removed when they are needed elsewhere. Solar cells can also be strapped to the back of a cell phone to recharge them on the go. Apparel with flxible cells weaved into them could be designed to power wearable technology…sky’s the limit really! Speaking of skies, flexible solar cells can also be incorporated into the aerodynamic body of an airplane to power it.
Xiaolin’s original motivation to work on this new type of solar cell stems from a comment made by her father in her hometown of Anshan in northeastern China.
“One day my father mentioned how great it would be if a building’s entire surface could be used for solar power, not just the roof, but also walls and windows”, says Zheng.
A decade later in 2010, Zheng was further inspired to pursue the idea after she read about an experiment in which nanometer graphene was successfully grown on the top of a silicon wafer. When the wafer was submerged in water, the nickel and graphene separated from the surface.
“It sounded unbelievable, like a magic trick, but they had achieved very reliable results” she recalls. Zheng tried to emulate the process for developing thin, flexible solar cells and found immediate success.
Conventional solar cells, unconventional manufacturing method
Regular solar cells are made on glass or silicon wafers which are heavy and rigid, limiting their use. Other surfaces such as paper or plastic are far more flexible; however they cannot withstand the high temperatures required for creating solar cells. If this new method of manufacturing flexible TFSCs is successfully replicated on an industrial scale, then flexible materials can be used for distribution, bringing down the cost of installation incredibly.
Zheng and her team began by applying a 300 nanometer layer of nickel to a silicon/silicon dioxide wafer. TFSCs were then deposited on the nickel. Another layer of protective polymer was applied on top of the TFSCs, followed by a layer of thermal release tape over it.
Next, the sandwich was submerged in room temperature water. One edge of the tape was peeled back so that water could seep between the nickel and the silicon/silicon dioxide wafer. Once the nickel was completely separated from the wafer, the researchers were left with a bare silicon wafer and the tape to which the polymer, TFSC and nickel layering remain attached.
The thermal tape along with its content were then heated to 90ºC (194ºF) for a few seconds. An adhesive was applied to the nickel; when the thermal tape was peeled off, all that was left was the polymer covered TFSC which could be stuck to any surface like a decal.
This process resulted in a solar cell that is no more than a couple microns thick and is flexible enough to be attached to any surface. The researchers also stated that their bendable solar cells have the potential to provide more or less the same power efficiencies their rigid counterparts do.
Besides offering a great new way to harness solar power, this method of making solar cells will also yield significant savings as it allows the silicon or glass substrate to be reused. More savings can be expected as these flexible cells do not require a rigid base material which accounts for about 25% of the solar cell’s cost.
Significant challenges ahead
Of course, this does not mean there are no challenges to overcome. Right now, the researchers are trying to find out if the process can be replicated on solar cells with higher efficiencies. They also have to figure out a way to ensure the peeling process can be done mechanically on large scales, as opposed to by hand, as is being done in the lab.
Because of their poorer power conversion efficiency, TFSCs need nearly twice as much installation space compared to regular c-Si cells, and their flexibility really isn’t anything to write home about.
The sticker like TFSCs, on the other hand, presents an entirely new dimension to the solar power industry. Sure, the rooftops may belong to high efficiency c-Si cells for the foreseeable future, but that does not mean there is no light to be harnessed from the side of the buildings, windows, shingles etc. Even if their efficiency does not catch up with regular rigid first gen solar cells, the fact that they will be much easier to make, and can be installed on any surface will open up plenty of options in the future.
Most solar panels you see on rooftops and solar power stations are made from crystalline silicon (c-Si), which is expensive to procure and work with.
They are also very rigid in construction, which limits their installation to flat surfaces only.
(Howwegettonext.com / Pinterest)
To get around this problem, researchers in the 1970s began experimenting with other substances which demonstrated photovoltaic properties -- amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS) showed promise. Solar cells made from any of these can be adapted to stick to a variety of different flexible substrates allowing them to be transported, and installed with greater ease.
The first TFSCs or thin film solar cells thus rolled out, and their adoption has been steadily increasing. Today, thin film solar cell represents 10% of the global solar power market.
One of the bigger advantages TFSCs offer over conventional solar cells is that they are about 30% cheaper, mainly due to the ease with which they can be installed. By 2009, TFSCs had won a respectable 18% of the market and it looked like they were well on their way to seeing widespread usage.
However, this was before cheaper c-Si solar panels from manufacturers in China began making inroads into the solar power market. Despite their higher price tag, traditional silicon-based solar cells still offer efficiencies much superior to what TFSCs can (commercially) provide. As Chinese manufacturers ramped up production, the cost of solar panels declined rapidly, making them a very attractive option for commercial and residential usage alike.
By 2012, the share of TFSC had slumped to 11%, and many manufacturers ended up declaring bankruptcy. In fact, the global market share of TFSC is expected to fall to 7% by 2017.
Innovative new peel and stick TFSCs promise a brighter future
This situation might change if a new type of sticker like TFSC developed by a team of enterprising researchers at Stanford University, US and Hanyang University, China finds its way to the manufacturing lines.
Led by Xiaolin Zheng at Stanford, and Professor Dong Rip Kim at Hanyang, the teams announced they had developed a way to create TFSCs which could be stuck to virtually any flexible surface. These cells not only have the potential to bring down the cost of manufacturing and installation even further, but open up a whole new way of using solar cells.
Imagine solar cells stuck to a window in your home, which can be removed when they are needed elsewhere. Solar cells can also be strapped to the back of a cell phone to recharge them on the go. Apparel with flxible cells weaved into them could be designed to power wearable technology…sky’s the limit really! Speaking of skies, flexible solar cells can also be incorporated into the aerodynamic body of an airplane to power it.
Xiaolin’s original motivation to work on this new type of solar cell stems from a comment made by her father in her hometown of Anshan in northeastern China.
“One day my father mentioned how great it would be if a building’s entire surface could be used for solar power, not just the roof, but also walls and windows”, says Zheng.
A decade later in 2010, Zheng was further inspired to pursue the idea after she read about an experiment in which nanometer graphene was successfully grown on the top of a silicon wafer. When the wafer was submerged in water, the nickel and graphene separated from the surface.
“It sounded unbelievable, like a magic trick, but they had achieved very reliable results” she recalls. Zheng tried to emulate the process for developing thin, flexible solar cells and found immediate success.
Conventional solar cells, unconventional manufacturing method
Regular solar cells are made on glass or silicon wafers which are heavy and rigid, limiting their use. Other surfaces such as paper or plastic are far more flexible; however they cannot withstand the high temperatures required for creating solar cells. If this new method of manufacturing flexible TFSCs is successfully replicated on an industrial scale, then flexible materials can be used for distribution, bringing down the cost of installation incredibly.
Zheng and her team began by applying a 300 nanometer layer of nickel to a silicon/silicon dioxide wafer. TFSCs were then deposited on the nickel. Another layer of protective polymer was applied on top of the TFSCs, followed by a layer of thermal release tape over it.
Next, the sandwich was submerged in room temperature water. One edge of the tape was peeled back so that water could seep between the nickel and the silicon/silicon dioxide wafer. Once the nickel was completely separated from the wafer, the researchers were left with a bare silicon wafer and the tape to which the polymer, TFSC and nickel layering remain attached.
The thermal tape along with its content were then heated to 90ºC (194ºF) for a few seconds. An adhesive was applied to the nickel; when the thermal tape was peeled off, all that was left was the polymer covered TFSC which could be stuck to any surface like a decal.
This process resulted in a solar cell that is no more than a couple microns thick and is flexible enough to be attached to any surface. The researchers also stated that their bendable solar cells have the potential to provide more or less the same power efficiencies their rigid counterparts do.
Besides offering a great new way to harness solar power, this method of making solar cells will also yield significant savings as it allows the silicon or glass substrate to be reused. More savings can be expected as these flexible cells do not require a rigid base material which accounts for about 25% of the solar cell’s cost.
Significant challenges ahead
Of course, this does not mean there are no challenges to overcome. Right now, the researchers are trying to find out if the process can be replicated on solar cells with higher efficiencies. They also have to figure out a way to ensure the peeling process can be done mechanically on large scales, as opposed to by hand, as is being done in the lab.
Because of their poorer power conversion efficiency, TFSCs need nearly twice as much installation space compared to regular c-Si cells, and their flexibility really isn’t anything to write home about.
The sticker like TFSCs, on the other hand, presents an entirely new dimension to the solar power industry. Sure, the rooftops may belong to high efficiency c-Si cells for the foreseeable future, but that does not mean there is no light to be harnessed from the side of the buildings, windows, shingles etc. Even if their efficiency does not catch up with regular rigid first gen solar cells, the fact that they will be much easier to make, and can be installed on any surface will open up plenty of options in the future.