It is well known that it can be very challenging to transform a process developed in the laboratory into a procedure that can be applied in large scale manufacturing. Where work in the laboratory is mainly focused on the actual “development of something new”, issues like scalability, materials cost, material consumption, safety, sustainability, etc. become equally important factors when facing actual manufacture.
A good example of this is the development of the organic solar cell, where motivation for research originated in the potential of flexible, low-cost devices prepared by fast Roll-to-Roll (R2R) manufacturing processes, ensuring a thin outline because the very low material consumption.
Research started out on glass substrates using ITO (indium tin oxide) as the transparent front electrode (a requirement for letting the sunlight pass), spin coating to deposit the multilayer stack and vacuum deposition to deposit the required back electrode to finalise the device.
For decades, this was the setup research on organic solar cells evolved around, and the main focus was quite naturally zoomed in on increasing the performance/efficiency of the organic solar cell. The cell size was most often kept to a minimum (down to a few mm2) in order overcome issues of sheet resistance, which had a negative effect on the performance when the solar cells increased in size.
The problem was that, when efficiencies started to reach a state that could be interesting for upscaling, basically nothing was aligned with a technology transfer – rigid substrates are not compatible with R2R processing, spin-coating is a non-additive manufacturing process with a huge materials waste, indium is a scarce metal which makes it a quite expensive part of a meant-to-be inexpensive solar cell and patterned vacuum deposition, although possible, is not a process associated with high speed manufacture.
Since then, much more effort has been put into finding processing solutions that are easily up-scalable, and in the MADRAS project we have strived to develop scalable solutions by using coating and printing techniques that have been used in the printing industry for decades/centuries like blade and slot-die coating, as well as screen and flexo printing.
Analogue approaches can be used towards other technologies using printed functional materials such as Perovskite solar cells, fuel cells, printed batteries, Li-ion electrodes, transistors, LEDs, sensors, etc.
Having the right laboratory equipment that can mimic the process of large-scale manufacturing is of course super important when developing and optimising processes and materials – especially when wanting to transfer from a development stage.
Below is a description of various small-scale setups that can be useful in a Lab-to-Fab process:
The flatbed laboratory coater is a very versatile coating machine as it allows for the use of both rigid and flexible substrates. The substrate is mounted on a base plate either to be held in place by taping it down or by use of a vacuum base plate which holds the substrate in place through suction. Scalable processing technics such as slot-die coating, knife coating, bar coating, pen coating and flexo printing can then easily be carried out along the substrate with a minimum material consumption.
Drying is typically performed through heating of the base plate. This drying process where the heat comes from below through contact is not typical in R2R processing, where hot air drying is more common. This can on rare occasions create differences in the dried films.
The drum coater is an example of the first step towards R2R processing using only flexible substrates. The processing is carried out over a heated drum and can be performed either as a simple experiment (3 feet of foil is attached to the surface of the drum) where an experiment is simply one turn of the drum. The experiment here mimics the results of the flatbed coater with heat coming from below (the backside of the foil). Alternatively, the drum coater can also be used in R2R mode.
In this case, experiments up to around 100 meters of foil can be conducted. The heating can is in this case be a combination of back side heating and/or heating from both sides when passing through an oven system. Such an oven can be based on hot air (or hot inert gas) and/or IR/UV drying and provides a drying process very similar to what can be expected in a large-scale process.
The laboratory R2R coater is basically a mini version of larger coating machines, which can be fitted with various ovens Hot air/inert gas, IR, UV… The major difference between this and a larger machine will typically be the processing speed, as the total oven length, and hence the drying capacity, will be lower and this limits the possible processing speed.
The huge advantage of the laboratory R2R coater is, among other things, the relatively low amount of material and time needed for conducting experiments and the optimisation of processes and materials. Also, the direct transfer of processing conditions to large scale R2R production is a major benefit when working in an industrial environment or with technologies that aims for large scale fabrication.
In MADRAS, we have used such small-scale setups to optimise the inks and device stacks developed within the project.
For more information about small scale setups that can be used for optimising processes for upscaling click here.
Roar Rønnow Søndergaard, PhD, Senior Developer at infinityPV
Has a background in synthetic organic chemistry and has worked with thin film and Roll-to-Roll processing of organic electronics since 2008 with a primary focus on organic solar cells.
Main focus area is currently within equipment development for processing and analysis of thin films.
infinityPV ApS is a leading Danish company focused on scaling printed solar cell technology and bringing it to market. On this path many techniques that were not in existence or not sufficient in pre-existing forms have been developed, re-developed and made available to the scientific community. As a tribute to the success of our activities, techniques such as LBIC, laboratory scale slot-die coating, cost efficient multichannel MPPT SMUs, solar simulators, roll-to-roll printing and coating technology, materials, solar cells and much more are available from us.