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Lab scale fabrication

Organic solar cell fabrication in a lab scale is generally considered as small scale manufacturing. The size of the produced solar cells are small, with the sizes ranging between $1 mm^2$ to $4 cm^2$DOI:10.1016/j.solmat.2013.05.034.

The most commonly used technique for producing cells is spin coating, as described in the spin coating section, where a substrate is spun at a high speed distributing the applied ink, however, an inherint issue with spin coating is the limited scalability with regards to processing.

In contrast to spin coating, linear coating techniques such as blade coating and slot die coating is seeing increasing use, since these have a better potential to be transfered to large scale manufacturing, however they have not yet shown solar cell efficiencies quite as high as what have been achieved using spin coating.

Spin coating on Glass ITO substrates

The typical organic solar cell is produced on a similar substrate to the one shown in Figure 1, with a single pre-patterned glass-ITO substrate. The substrate has 6 separate cells defined with a size of 2 mm by 2 mm.

Figure 1. Example of a ITO glass substrate with 6 individual cells. The bare substrate (left) has a ITO pattern with 2 by 3 stripes pre-patterned. (center) After spin coating a thin PEDOT:PSS layer. (right) Illustration of the cells; blue is the pre-pattterned ITO, gray is the metallic top electrode and orange indicated the 6 individual cells.

The cell would be manufactured using spin coating for a hole blocking PEDOT:PSS layer, a donor:acceptor active layer and evaporation for a top electrode layer.DOI:10.1002/adma.200802559

Slot-die coating on PET

In the following an example of solar cells produced using primarily slot-die coating is presented. The manufacturing is completed on a lab scale roll coaterDOI:10.1016/j.solmat.2011.08.027DOI:10.1016/j.solmat.2012.09.008 using the same methods as on larger roll-2-roll coating machinery. The principle of the machine is to use a heated drum on which a PET foil substrate is mounted. The materials can then be coated using a slot-die coating head on the mounted foil. The heated drum dries out the solvents from the applied solutions, enabling coating of several layers directly on the film, without removing the substrate from the drum. Several examples of coated materials are shown in Figure 2, with both active material layers and conductive layers presented. The stripes shown are 13 mm wide

Figure 2. Examples of slot die coated films on a lab scale roll coater. Images shows (left) the coating of a yellow active layer, with a dried film and a wet film. (middle) a orange active layer material with three dried film and the fourth being coated. (right) coating of a conductive PEDOT:PSS stripe ontop of the active layer. All of the stripes above are coated on a PET foil with ITO electrodes and in 13 mm width.

General methods for making the top electrodes tends to be by evaporation of metal, screen printing or slot-die coating of conductive inks. An example of a set of 10 screen printed 1 cm2 organic solar cells are shown in Figure 3, where a commercial silver paste is used.

Figure 3. Example of screenprinting of slot-die coated solar cells with a 1 cm2 electrode pattern.
DOI:10.1016/j.solmat.2008.10.004

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