Nanotech 2010

Volume Grain Analysis in Organic Thin Film Semiconductors

D. Bergman, K.P. Gentry, T. Gredig
California State University Long Beach, US

Keywords: organic semiconductor, thin film, grain distribution, phthalocyanine, atomic force microscopy


The grain structure of organic thin films is quantitatively studied and includes the precise grain area and volume distributions. The grain morphology affects the device performance of gas sensors and organic solar cells due to trap states at grain boundaries. Phthalocyanine thin films are deposited onto sapphire substrates. It was found that the average grain size can be controlled from 30-200 nm in phthalocyanine films deposited between room temperature and 260 oC. The grain distributions of minor and major axis are different and can be described with either a normal or log-normal distribution. For comparison with experimental data, analytical models for grain growth exist, but these models are based on three-dimensional grains. A quantitative analysis of the three-dimensional grain size in phthalocyanine thin films is presented. Comparison of areal and volume grain distributions show that the volume distribution is more narrow and does not show rare events of large grains, which are predicted by a random nucleation and growth process. Rather, the asymmetry of the small molecule seems to play a role in the distribution. This research is supported by a NSF CAREER DMR- 0847552 grant.
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