Organic Solar Cells with Slot-Die Coated PM6:Y6 Layer

An organic solar cell (OSC) is a form of PV that uses organic electronics, a field of electronics that uses conductive biopolymers or tiny organic compounds to generate light absorption and electrostatic interactions to generate energy through the photoelectric cell. OSCs make up the majority of natural solar cells, as stated in Chem Rxiv magazine.

To learn: Environmentally friendly and roller-processed flexible organic solar cells based on PM6: Y6. Image Source: Thongsuk7824 / Shutterstock.com

Organic solar cells (OSCs) achieve continuously higher efficiencies thanks to non-fullerene receivers that enable precise control of the amount of energy and the absorption capacity with different donor substances.

Photovoltaics with organic materials, combined with the adaptability of organic molecules, can be inexpensive for solar applications. Since organic compounds have high optical absorption efficiency, a large light intensity can be collected with a small number of materials. Compared to other (PV) innovations, OSCs offer attractive properties such as low price, mechanical stability, low weight and the ability to be semi-transparent.

(left) Representation of the inverted OSC used for this study.  (right) Absorption of photoactive materials in O-XY (16 mg / mL) with slot nozzle coating at 100 ° C.

(Left) Representation of the inverted OSC used for this study. (to the right) Absorption of photoactive materials in O-XY (16 mg / mL) with slot nozzle coating at 100 ° C. Image source: Castro, M., et al., Chem Rxiv

All of this makes OSCs one of the most attractive photovoltaic devices and attracts a lot of research interest to bring them to market. In addition, there is a potential difference in productivity between solar cells made using laboratory-scale processes and those made using industry-compatible technologies.

Why slot die coating with PM6: Y6?

Designed to be compatible with roll-to-roll manufacturing, slot nozzle coating, blade coating, or even aerosol coating are by far the most reliable adaptable manufacturing processes for OSCs. The slot-die coating, on the other hand, is preferred because it enables a one-dimensional arrangement in the form of one or even several strips with a very well-defined width and almost without wasting resources. Therefore, slot-die coating should be the preferred method for high-efficiency devices in order to close the “lab-to-fab gap”.

Statistical representation of the measured PV parameters of PM6: Y6 devices manufactured at different temperatures: a) Power conversion efficiency (PCE) and b) Fill factor (FF)

Statistical representation of the measured PV parameters of PM6: Y6 devices manufactured at different temperatures: a) Power Conversion Efficiency (PCE) and b) Fill Factor (FF). Image source: Castro, M., et al., Chem Rxiv

Dozens of new new donors and acceptors, particularly PM6 donors with Y6 acceptor materials, have appeared recently. When using green solvents, the researchers showed remarkable efficiency of over 15% on rigid materials.

The absorbed PM6 reflects exactly the largest spectroscopic irradiation point in the solar spectrum, while Y6 complements this absorption in the red region of the spectrum. This makes the mixture of substances PM6: Y6 an excellent choice for bridging efficiency differences between different production processes.

Manufacturing methods

The transfer of PM6: Y6 electronics to roller production on various substrates using scalable production processes such as slot nozzle lamination is still required. However, because PM6 exhibits temperature-dependent aggregation (TDA), it must be preheated during the slot die coating technique in order to remain fluid. In this situation the substrates, tubes, syringes and slot nozzle heads are heated during the entire coating process.

PM6: Y6 slot nozzle coated at a) 100 ° C and b) 120 ° C.  c) Influence of the AL thickness on the transparency of the ITO / ZnO / AL stack in relation to a window light.

PM6: Y6 wide slot nozzle coated with a) 100 ° C and B) 120 ° C. C) Influence of the AL thickness on the transparency of the ITO / ZnO / AL stack in relation to a window light. Image source: Castro, M., et al., Chem Rxiv

The possibility of the slot die coating of PM6: Y6 in the outdoor area on composite materials based on a green solution without additives has been proven. The improvement in the coating variables is illustrated. Now that significant efficiencies have been achieved using laboratory-scale procedures, the results can easily be transferred to a roll-to-roll platform; This is critical to increasing the profitability of this innovation.

Recently it has been shown that the use of PM6: Y6 as active materials and a heated slot nozzle coating over an ITO coated sample at the same temperature as the solvent gives an efficiency of over 15%. These efficiencies were achieved without adding 16 mg / ml in the green solvents O-XY or trimethylbenzene (TMB).

The short-circuit current is increased at higher temperatures. If the temperature rose above 100 ° C, the solvents dried more quickly and there was agglomeration of substances at both corners of the AL, horizontal to the direction of the coating.

The above effect causes inhomogeneities and streaks, which has a direct impact on the efficiency of the end product. Charge transport recombination is important in determining the resulting PV properties because recombination means that the electrons are lost before they reach the electrodes. The light intensity dependence of current and open circuit voltage can be used to analyze the degree and dominant type of recombination.

Researchers predict the recombination process at open circuit voltages in order to obtain different and complementary information about recombination processes that occur in the OSCs coated at different temperatures. Increasing the AL thickness also affects the efficiency of the device.

A thick AL increases light absorption and also makes the final product more durable, which is crucial when using roll to roll as the process involves printing, folding and stretching. Thinner AL layers enable semi-transparent components, which are attractive for a large number of applications, as well as the reduction of charge carrier paths, whereby the probability of a recombination up to absorption in the component electrodes is reduced.

The researchers applied the hot slot nozzle coating with a solution based on the temperature-aggregated behavior of the mixture and found that by synchronizing the flexible heating rate with the hot slot nozzle head at 100 ° C, they were able to achieve the desired results.

Note: This paper is a pre-printed form.

References

Castro, M., et al. (2021). Environmentally friendly and roll-processed flexible organic solar cells based on PM6: Y6. Chem. Rxiv. 11/25/2021 Version 3.https: //chemrxiv.org/engage/chemrxiv/article-details/619f5d1b784805839a9a5940

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