David Savastano, Editor11.07.14
There are many methods to producing printed electronics systems, and researchers and manufacturers alike are trying to design methods to improve their products. Some of the most interesting work in occurring in the labs at research institutes.
In a major development, scientists from Solliance, a thin-film solar cell research alliance, reported that they produced the world’s first organic photovoltaics (OPVs) to be made exclusively with inkjet printing processes.
Solliance added that the processes offer complete flexibility of cell shape, substrate and structure, and are ideal for rapid product development and prototyping as well as up-scaling to volume manufacturing of cost-effective products. According to Solliance, the all-inkjet-printed OPVs were created with standard, affordable materials and are free of indium tin oxide (ITO), further reducing production costs and the use of scarce raw materials such as indium.
Ronn Andriessen, program manager OPV at Solliance, said that for all the required electro-active layers needed to create OPV devices, cells and modules, dedicated inks needed to be developed.
“The inks we developed are quite complex from composition as all parameters need to be in place at once (stability, active ingredient concentration, surface tension, viscosity, wetting, pinning, leveling, adhesion and performance),” Andriessen said. “Hence, in all inks, additional components and solvents were added in order to enable this.
“The most difficult one was the ink formulation of the photo-active layer,” Andriessen added. “This typically consists of a blend of two organic compounds (mostly used is a blend of an absorbing p-type polymer and a fullerene molecule as n-type semi-conductor).
Andriessen said that the ink should be:
Andriessen said that the tests were run on sheet-to-sheet (S2S) systems, but Solliance is developing roll-to-roll (R2R) capabilities.
“Our experiments were run on S2S inkjet printers, but we are setting up R2R inkjet infrastructure at this very moment,” he added.
“The number of nozzles/head give a good indication of the average width that can be printed during one single printing step. For 1024 nozzles/head, this is about 7 cm, hence for e.g. a 30 cm wide web (for R2R printing), this would mean that (only) five stitched printheads would be needed. Our average printing speed (for a single OPV device, we print six layers) is currently 5 to 10 m/min.
“As the used inks are still in development, there is definitely room for improvement in terms of printing speed by further optimizing the ink properties,” he added. “In graphics applications, printing speeds of 20 to 30 m/min are nowadays common. Hence, we believe that inkjet print technology, with full flexibility of shape (printing on demand) is a very attractive and versatile production technology for OPV’s future applications. Basically, any form and shape can be designed and directly printed, without material losses.”
Andriessen said that inkjet printing has improved in the last few decades, making this type of project more feasible.
“Of course in general, the developments in inkjet head technologies the last five to 10 years widened further the operational window of inkjet printing, which put a little less stress on the ink formulation and made it finally possible to realize in a much shorter time as had been the case 20 years ago,” Andriessen said.
As all functional OPV layers are inkjet printed and the maximum processing temperature stays always below 130°C, any substrate with a Tg around 110°C or higher can be used,” Andriessen noted. “This includes low cost PET, but also PEN and other substrates like metal (foil), glass and paper. There are no vacuum steps and everything can be executed under ambient conditions (expect temperature during drying/annealing).
“The efficiencies we obtain so far by inkjet printing six functional OPV layers are ≥ 75% of the spin coated lab samples,” Andriessen added. “The efficiency is related to the photo-active blend that is used. Today, several blends are available that yield over 9% to 10% efficiency. For higher efficiencies, additional junctions are needed, but due to our approach, for each additional junction, only three additional layers need to be printed of which only one is a new one: a complementary absorbing photo-active layer. The ZnO and PEDOT can be re-used and re-printed. Our process yield is currently ≥ 85%, with still room for further improvements, of course.”
Andriessen noted that Solliance will not commercialize this, but as this development was partially executed within a partnership with DisaSolar of France, some of the developed processes will definitely be implemented in the OPV production at DisaSolar in about two years.
“DisaSolar is a company already specialized in making customized flexible PV by adapting existing thin film PV modules according to their customers’ wishes,” Andriessen said. “Their current customers are not really interested in cost/Wp, but in added functionality for a given application with a predefined format and shape.
“By using inkjet printing of OPV, the ability to customize is embedded in the print technology itself: any form, any shape (and even color) of an OPV cell and/or module can be made, and this without material losses,” Andriessen concluded. “This is important due to the material-driven cost structure of OPV.
Of course, other existing companies or new companies can also have access to this technology via partnerships with Solliance.”
The UK-based Centre for Process Innovation (CPI) is working on a variety of projects. One of the most promising is the progress being made on the development of flexible displays and screens, with a novel process for fabricating bendable organic thin film transistor (OTFT) arrays.
CPI’s research allows these OTFT arrays to be bent to a radius of 1mm without a major reduction in device performance. According to CPI, this could allow the production of roll-up televisions or mobile phones, as well as paper-like documents like animated newspapers or magazines.
CPI reported that the first flexible plastic-based demonstrator display units using CPI’s OTFT technology will be completed during 2014, as a part of the Technology Strategy Board funded, CPI project ROBOLED.
CPI also recently announced that it has produced a range of flexible organic light emitting diode ( OLED ) demonstrators, manufactured on its OLED/OPV Prototyping Line.
Belgium-based imec reported it has developed fullerene-free organic photovoltaic (OPV) multi-layer stacks achieving a conversion efficiency of 8.4%. Imec reported its findings in a recent Nature Communication. Imec’s researchers added that this would allow OPV cells to become more competitive in the thin-film photovoltaics marketplace, as OPVs are ideal for flexible substrates.
These projects are all in the relatively early stages, yet they hold much promise for the possibilities for flexible and printed electronics in the future.
In a major development, scientists from Solliance, a thin-film solar cell research alliance, reported that they produced the world’s first organic photovoltaics (OPVs) to be made exclusively with inkjet printing processes.
Solliance added that the processes offer complete flexibility of cell shape, substrate and structure, and are ideal for rapid product development and prototyping as well as up-scaling to volume manufacturing of cost-effective products. According to Solliance, the all-inkjet-printed OPVs were created with standard, affordable materials and are free of indium tin oxide (ITO), further reducing production costs and the use of scarce raw materials such as indium.
Ronn Andriessen, program manager OPV at Solliance, said that for all the required electro-active layers needed to create OPV devices, cells and modules, dedicated inks needed to be developed.
“The inks we developed are quite complex from composition as all parameters need to be in place at once (stability, active ingredient concentration, surface tension, viscosity, wetting, pinning, leveling, adhesion and performance),” Andriessen said. “Hence, in all inks, additional components and solvents were added in order to enable this.
“The most difficult one was the ink formulation of the photo-active layer,” Andriessen added. “This typically consists of a blend of two organic compounds (mostly used is a blend of an absorbing p-type polymer and a fullerene molecule as n-type semi-conductor).
Andriessen said that the ink should be:
- Stable at room temperature at a given concentration (i.e. relates to the desired final dry layer thickness).
- Should not contain any chlorinated solvents due to environmental restrictions.
- Should show stable droplet formation when fired with the (industrial) printing head at decent firing frequencies (> 1 kHz).
- Should pin on the receiving substrate (can be both on an already deposited layer as well as on the substrate).
- Should wet and level sufficiently to form a closed and homogeneous layer.
- Should be able to yield high performance at the end, which is related to an ideal phase separation, which in turn is a result of the correct solvent system in combination with a correct drying and annealing trajectory.
Andriessen said that the tests were run on sheet-to-sheet (S2S) systems, but Solliance is developing roll-to-roll (R2R) capabilities.
“Our experiments were run on S2S inkjet printers, but we are setting up R2R inkjet infrastructure at this very moment,” he added.
“The number of nozzles/head give a good indication of the average width that can be printed during one single printing step. For 1024 nozzles/head, this is about 7 cm, hence for e.g. a 30 cm wide web (for R2R printing), this would mean that (only) five stitched printheads would be needed. Our average printing speed (for a single OPV device, we print six layers) is currently 5 to 10 m/min.
“As the used inks are still in development, there is definitely room for improvement in terms of printing speed by further optimizing the ink properties,” he added. “In graphics applications, printing speeds of 20 to 30 m/min are nowadays common. Hence, we believe that inkjet print technology, with full flexibility of shape (printing on demand) is a very attractive and versatile production technology for OPV’s future applications. Basically, any form and shape can be designed and directly printed, without material losses.”
Andriessen said that inkjet printing has improved in the last few decades, making this type of project more feasible.
“Of course in general, the developments in inkjet head technologies the last five to 10 years widened further the operational window of inkjet printing, which put a little less stress on the ink formulation and made it finally possible to realize in a much shorter time as had been the case 20 years ago,” Andriessen said.
As all functional OPV layers are inkjet printed and the maximum processing temperature stays always below 130°C, any substrate with a Tg around 110°C or higher can be used,” Andriessen noted. “This includes low cost PET, but also PEN and other substrates like metal (foil), glass and paper. There are no vacuum steps and everything can be executed under ambient conditions (expect temperature during drying/annealing).
“The efficiencies we obtain so far by inkjet printing six functional OPV layers are ≥ 75% of the spin coated lab samples,” Andriessen added. “The efficiency is related to the photo-active blend that is used. Today, several blends are available that yield over 9% to 10% efficiency. For higher efficiencies, additional junctions are needed, but due to our approach, for each additional junction, only three additional layers need to be printed of which only one is a new one: a complementary absorbing photo-active layer. The ZnO and PEDOT can be re-used and re-printed. Our process yield is currently ≥ 85%, with still room for further improvements, of course.”
Andriessen noted that Solliance will not commercialize this, but as this development was partially executed within a partnership with DisaSolar of France, some of the developed processes will definitely be implemented in the OPV production at DisaSolar in about two years.
“DisaSolar is a company already specialized in making customized flexible PV by adapting existing thin film PV modules according to their customers’ wishes,” Andriessen said. “Their current customers are not really interested in cost/Wp, but in added functionality for a given application with a predefined format and shape.
“By using inkjet printing of OPV, the ability to customize is embedded in the print technology itself: any form, any shape (and even color) of an OPV cell and/or module can be made, and this without material losses,” Andriessen concluded. “This is important due to the material-driven cost structure of OPV.
Of course, other existing companies or new companies can also have access to this technology via partnerships with Solliance.”
The UK-based Centre for Process Innovation (CPI) is working on a variety of projects. One of the most promising is the progress being made on the development of flexible displays and screens, with a novel process for fabricating bendable organic thin film transistor (OTFT) arrays.
CPI’s research allows these OTFT arrays to be bent to a radius of 1mm without a major reduction in device performance. According to CPI, this could allow the production of roll-up televisions or mobile phones, as well as paper-like documents like animated newspapers or magazines.
CPI reported that the first flexible plastic-based demonstrator display units using CPI’s OTFT technology will be completed during 2014, as a part of the Technology Strategy Board funded, CPI project ROBOLED.
CPI also recently announced that it has produced a range of flexible organic light emitting diode ( OLED ) demonstrators, manufactured on its OLED/OPV Prototyping Line.
Belgium-based imec reported it has developed fullerene-free organic photovoltaic (OPV) multi-layer stacks achieving a conversion efficiency of 8.4%. Imec reported its findings in a recent Nature Communication. Imec’s researchers added that this would allow OPV cells to become more competitive in the thin-film photovoltaics marketplace, as OPVs are ideal for flexible substrates.
These projects are all in the relatively early stages, yet they hold much promise for the possibilities for flexible and printed electronics in the future.
