(Invited) Polymer Nanopatterned Layers for Organic Solar Cell Applications

Recent advances in polymer-based organic solar cells have been possible due to different approaches such as design of new devices and synthesis of new materials with low band-gaps, control of the nanoscale morphology with additives, variation of the ratio of the donor/acceptor in the bulk heterojunction, application of thermal or solvent annealing process, the use of polymer nanostructures (nanogratings, nanopillars, nanorods and nanodots), etc. [1-5]. Nanoporous anodic alumina templates (NAAT) have been used to obtain polymer nanopatterned layers [6]. Template synthesis has been demonstrated to be an excellent technique to transfer the nanoporous shape to polymer and it is a cost-effective technique.

In an organic bulk heterojunction solar cell is very important to improve the exciton dissociation, charge transport and to reduce the recombination. Polymer nanopatterned structures allow that the excitons can reach until the donor/acceptor interface to be dissociated into electrons and holes and the free charge carriers can travel along the uninterrupted pathway until they reach their respective electrodes. Interdigitated polymer nanostructures allow the domains in the p-type donor material (polymer) and the n-type acceptor material (fullerene) to be aligned normal to the electrode surfaces, thus increasing their crystallinity and charge carrier mobility and reducing recombination rates inside the device [7].

In this scenario, herein, we present the manufacture of the NAAT and interdigitated morphology to obtain the nanopatterned organic solar cell. Figure 1a and 1b show the environment scanning electron microscopy (ESEM) images of NAAT and P3HT-nanopatterned structure. Fig. 1c shows the nanopatterned device with the stack ITO / PEDOT:PSS / poly (3-hexylthiophene) P3HT-nanopatterned / [6,6]-phenyl-C₇₁-butyric acid methyl (PC₇₀BM)  / Ca / Ag. Furthermore, we characterized and analysed the current-voltage characteristic of this solar cell measured under light and dark conditions. Finally, we discuss the future and potential applications of the NAAT to be used in nanopatterned layers manufactured with other semiconductor materials.

References

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[7] Yang Y., Mielczarek K., Aryal M., Zakhidov A., Hu W., ACS Nano, 2012, 6,  2877.

Acknowledgements

This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant No. TEC2012-34397 and AGAUR 2014 SGR 1344.