Nano-pathways: Bridging the divide between water-processable nanoparticulate and bulk heterojunction organic photovoltaics

• Published in: Nano energy 2015-11, Vol.19
• Main Authors: Holmes, Natalie P., Marks, Melissa, Kumar, Pankaj, Kroon, Renee, Barr, Matthew G., Nicolaidis, Nicolas, Feron, Krishna, Pivrikas, Almantas, Fahy, Adam, Mendaza, Amaia Diaz de Zerio, Kilcoyne, A. L. David, Müller, Christian, Zhou, Xiaojing, Andersson, Mats R., Dastoor, Paul C., Belcher, Warwick J.
• Format: Article
• Language: English
• Subjects: Blend morphology; Glass transition temperature; Nanoparticle; Organic photovoltaic; Scanning transmission X-ray microscopy; SOLAR ENERGY; Water processable solar cells
• ISSN: 2211-2855

In this paper, we report the application of a conjugated copolymer based on thiophene and quinoxaline units, namely poly[2,3-bis-(3-octyloxyphenyl)quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1), to nanoparticle organic photovoltaics (NP-OPVs). TQ1 exhibits more desirable material properties for NP-OPV fabrication and operation, particularly a high glass transition temperature (Tg) and amorphous nature, compared to the commonly applied semicrystalline polymer poly(3-hexylthiophene) (P3HT). This study reports the optimisation of TQ1:PC71BM (phenyl C71 butyric acid methyl ester) NP-OPV device performance by the application of mild thermal annealing treatments in the range of the Tg (sub-Tg and post-Tg), both in the active layer drying stage and post-cathode deposition annealing stage of device fabrication, and an in-depth study of the effect of these treatments on nanoparticle film morphology. Finally and in addition, we report a type of morphological evolution in nanoparticle films for OPV active layers that has not previously been observed, that of PC71BM nano-pathway formation between dispersed PC71BM-rich nanoparticle cores, which have the benefit of making the bulk film more conducive to charge percolation and extraction.