Improving performance of polymer photovoltaic devices using an annealing-free approach via construction of ordered aggregates in solution

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Abstract
Low crystalline order has been proved to be one of the main hindrances for achieving high performance devices based on thin films composed of crystallizable polymer. In this work, we use a facile method to substantially improve crystallinity of poly(3-hexylthiophene) (P3HT) in its pure or composite film via the construction of ordered precursors in the solution used for thin film deposition. These improvements have been confirmed by bright-field transmission electron micrography, electron diffraction, UV-Vis absorption and wide-angle X-ray diffraction. The electrical conductivity of thus obtained P3HT films is increased by almost two orders of magnitude. Polymer solar cells based on P3HT:PCBM ([6,6]-phenyl C61 butyric acid methyl ester) composite fabricated using this method achieve power conversion efficiencies (PCEs) as high as 3.9%, which is almost four times that of pristine devices and also higher than thermally-annealed devices under the same measurement conditions. This simple method paves the way for the fabrication of high performance devices with an “annealing-free” approach, and enriches the ways to improve crystalline order in thin films comprising crystallizable polymers.

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