Effect of printing parameters and annealing on organic photovoltaics performance
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In this paper, ink-jet printing was used to deposit poly(3-hexylthiophene):phenyl-C61-butyric acid methyl ester blend as active layer and a comparison study of three printing methods [multiarray (MA), single layer array, and multilayer array] was performed. For organic photovoltaics (OPVs) fabricated using MA or multilayer arrays, the efficiency was less than 1% independent of printing parameters. When single layer print pattern was used, the device performance improved significantly and an efficiency of 1.29% was obtained, indicating that the thin films fabricated using a single layer are more suitable for OPVs than films obtained by overlapping of multiple layers. The influence of annealing parameters on electrical and optical thin film properties was also investigated. The study found that the optimum annealing condition for the printed OPVs is solvent annealing at 60 °C, yielding an efficiency of 1.99%.
I. INTRODUCTION
In the last two decades, concerns about rising energy demands have resulted in a concentrated search for costeffective alternative renewable sources of energy. Organic photovoltaics (OPVs) based on conjugated polymers and fullerene derivatives have gained considerable interest, as they seem to be potentially well suited to address the above-mentioned needs.1–3 There has been over the last decade a misnomer that OPVs would not require some of the clean room conditions required by their thin film counterparts. However, this is not the case, and equal care in cleanliness and a number of different deposition steps are required. Nevertheless, in simple quantity of materials, OPVs have significant advantages, which include less physical semiconductor materials required for a similar photonic response in generating excitons, devices produced require fewer industrial steps, and of course, one of the biggest benefits is that they are lightweight and can be deposited in many ways.4 The processability of organic semiconductors at room temperatures allows us to use simple deposition techniques such as spin-coating, doctorblading, or ink-jet printing. Ink-jet printing as a solution-dispensing tool has many attractive features due to its precise and versatile deposition technique.5–7 Its noncontact deposition technique makes it substrate and application independent allowing printing on flexible and nonflat substrates of different sizes. It allows the dimensional controlled deposition of inks on targeted locations up to micron-scale accuracy. a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2012.217 J. Mater. Res., Vol. 27, No. 16, Aug 28, 2012
The two-dimensional (2D) patterning ability negates the need of masks and thus, an extra fabrication step. This tight control also helps in keeping the wastage of materials to a minimum. As such, the technique is favorably disposed toward integration in industrial scale production, providing cost reduction of existing components as well as provides opportunities for pioneering new strategies. In addition, high mechanical flexibility has be
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