Water Based Inkjet Material Deposition of Donor-Acceptor Nanocomposites for Usage in Organic Photovoltaics

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Water Based Inkjet Material Deposition of Donor-Acceptor Nanocomposites for Usage in Organic Photovoltaics Anirudh R. Penmetcha1, Chenyu Zheng1 and Christopher J. Collison1,2,3 1 School of Chemistry and Materials Science, Rochester Institute of Technology, Rochester NY 14623 2 Nanopower Research Laboratory, Rochester Institute of Technology, Rochester NY 14623 3 Microsystems Engineering, Rochester Institute of Technology, Rochester NY 14623 ABSTRACT P3HT: PCBM nanoparticle based inks were fabricated using the miniemulsion technique [1]. The nanoparticles were characterized for their size using a quasi-elastic light scattering technique. The average diameter of P3HT:PCBM nanoparticles was found to be 52nm. The blending of the P3HT and the PCBM was tested using UV-Vis absorbance and fluorescence spectroscopy – it was found that the blend ratio of the nanoparticle can be controlled by varying the individual concentrations of the P3HT and PCBM in chloroform ("the oil phase") of the miniemulsions. Finally the P3HT:PCBM nanoparticle inks were inkjet printed onto PEDOT:PSS coated ITO substrates to form the active layer of the organic photovoltaic cell. Aluminum cathodes were evaporated onto the printed nanoparticle active layer film to form functioning OPVs. The best power conversion efficiency for one of these devices was 0.07%. INTRODUCTION Organic photovoltaics offer the promise of quick, inexpensive roll-to-roll solution processing of solar cells. However the majority of active-layer materials used to make OPVs are generally dissolved in either aromatic or chlorinated solvents [2] - this poses a major challenge for a scaling up process as aromatic solvents pose a threat of flammability and chlorinated solvents are carcinogenic and pose serious threats to the environment and human health. A logical solution to this would be to design active layer materials that are soluble in “non-toxic” solvents like water and ethanol, but this would require a paradigm shift in terms of OPV materials design. To counter this, active layer nanoparticles are made by using the miniemulsion method [1] and suspended in water, and then inkjet printed to fabricate a prototype OPV device using an ink created out of this suspension. Here, inkjet printing is used as the “roll-to-roll analogue” instead of conventional coating techniques such as slot-die coating and screen printing [2,11,12] . Inkjet printing is a non-contact method of printing; less material is wasted in inkjet printing because the printer is designed to “drop-on-demand” and requires only 2-3ml of formulated ink to print devices - this makes it very convenient to pattern the substrate. The present study describes two goals. Firstly, to synthesize and characterize a waterbased nanoparticle ink consisting of poly(3-hexylthiophene-2,5-diyl) as the donor (P3HT) and phenyl-C61-butyric acid methyl ester as the acceptor (PCBM). Blending of the PCBM within the P3HT nanoparticle was confirmed by UV-Vis absorbance and fluorescence spectroscopy – it is crucial that the PCBM is sufficiently b