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Roll-to-roll processing

In the field of electronic devices, roll-to-roll processing, also known as web processing,^[1] reel-to-reel processing or R2R,^[2] is the process of creating electronic devices on a roll of flexible plastic, metal foil, or flexible glass.^[3] In other fields predating this use, it can refer to any process of applying coating, printing, or performing other processes starting with a roll of a flexible material and re-reeling after the process to create an output roll. These processes, and others such as sheeting, can be grouped together under the general term converting. When the rolls of material have been coated, laminated or printed they can be subsequently slit to their finished size on a slitter rewinder.
Large circuits made with thin-film transistors and other devices can be patterned onto these large substrates, which can be up to a few metres wide and 50 km (31 mi) long.^{[citation needed]} Some of the devices can be patterned directly, much like an inkjet printer deposits ink. For most semiconductors, however, the devices must be patterned using photolithography techniques.
Roll-to-roll processing of large-area electronic devices reduces manufacturing cost.^[4][2] Most notable would be solar cells, which are still prohibitively expensive for most markets due to the high cost per unit area of traditional bulk (mono- or polycrystalline) silicon manufacturing. Other applications could arise which take advantage of the flexible nature of the substrates, such as electronics embedded into clothing, large-area flexible displays, and roll-up portable displays.
A crucial issue for a roll-to-roll thin-film cell production system is the deposition rate of the microcrystalline layer, and this can be tackled using four approaches:^[5]
The roll-to-roll processing has been used in the manufacture of electrochemical devices such as batteries,^[6] supercapacitors,^[7] fuel cells,^[8][9] and water electrolyzers.^[10] Here, the roll-to-roll processing is utilized for electrode manufacturing and is the key to reducing manufacturing cost^[11] through stable production of electrodes on various film substrates such as metal foils, membranes, diffusion media, and separators.

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