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Earth receives enough sunlight in one hour to satisfy all human needs in a year. Using solar energy will reduce harmful CO2 emissions and resolve the forthcoming energy deficit. The market for stable, mass-produced Organic Solar Cells is estimated at one billion Euros by 2016.

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ESTABLIS will train a team of 11 PhDs and 4 Postdocs to become the scientific leaders in industry and academia. ESTABLIS Fellows will excel.

Research on organic solar cells

Complementarity is at the heart of Establis. To develop Organic Solar Cells requires a concerted combination of physical, synthetic and modelling capabilities. Establis members are working together–across preconceived scientific boundaries–to accelerate the production of Organic Solar Cells.

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Our Industrial Partners and Associate Partners ensure that the training and technology is economically feasible.

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The EEC is constructively investing more than 3.9 M€ in Establis to train, research and collaborate at the highest international level and ensure our energy platform for the 21st century.

Scientific results

SSSI 2013 - Characterization of the degradation process of Si-PCPDTBT: PC70BM (1:2) blend layers deposited on ITO/glass substrate

 

 

M. SECK1, 2, A. ŠATKA1,2, A. VINCZE1,2, D. HAŠKO1, F. UHEREK1,2, A. TOURNEBISE3

1International Laser Centre, Ilkovičova 3, 841 04 Bratislava, Slovakia.

2Institute of Electronics and Photonics, Slovak University of Technology, Ilkovicova 3, 812 19 Bratislava, Slovakia.

3Eberhard Karls Universität Tübingen, Institut für Physikalische und Theoretische Chemie, Auf der Morgenstelle, 18 72076 Tübingen, Germany.

Corresponding author e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.



In order to understand the degradation processes of materials used in organic photovoltaic devices, Si-PCPDTBT: PC70BM blend layers were investigated using time of flight secondary ion mass spectrometry (ToF-SIMS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The layers were degraded using a solar simulator (AM1.5G Xenon lamp) at ambient air for various times. Monitoring of the UV absorption loss was used as a degradation indicator. The comparison of the ToF-SIMS depth profiles of the unexposed and degraded samples in Fig.1 reveals remarkable increase of the 16O and 18O ions fragment intensity with the degradation time due to the diffusion of the atmospheric oxygen during the UV photo-ageing. According to the composition of the layers, a progressive increase of the NO, NO2, SO, SO2 ions fragment intensity caused by a possible oxidation of the active polymer material (Si-PCPDTBT: PC70BM) is evident. By measuring the depth of the crater (not shown here) created during the ToF-SIMS depth profiling, a significant decrease of the photoactive layer thickness was observed. The thickness of the non-degraded (0% UV loss) Si-PCPDTBT: PC70BM layer is approximately 340 nm and it became decreased to 260 nm after the photo-ageing resulting in 77% UV loss (1457h).

 

0% UV loss (0h)                                                                           77% UV loss (0h)

 

Fig.1: ToF-SIMS depth profiles of Si-PCPDTBT: PC70BM/ITO/glass without (left) and after the degradation resulting in 77% of UV loss (right)

The AFM surface morphology in Fig. 2 reveal good crystallinity of the layers, preserved also after the photo-ageing resulting in 77% UV loss. This is reflected in negligible change of the RMS roughness values, where Sq = 4.4 nm for non-degraded layer and Sq = 4.3 nm for 77% UV loss degradation. Also visible are the “holes” on the surface of the layers, with periodicity not clearly expressed.

 

Fig. 2: AFM images of Si-PCPDTBT: PC70BM blend layers before 0% (left) and after the degradation resulting in 77% of UV loss (right)

SEM SE images in Fig. 3 reveal flat surface of the unexposed layer, with morphology features very similar to that observed in AFM images. Rarely, some clusters of the organic material were found on the surface (e.g. marked in Fig. 3), and these were attributed to the technological imperfections. However, nano-objects homogeneously dispersed over the layer surfaces were observed on degraded samples. On the most degraded layer, the objects (white in the SEM SE image) have a clear fibril form lying on the layer surface. SIMS depth profiles obtained during the initial nearly 200s etching time clearly reveals higher oxygen content in these nano-objects formed during photo ageing. The oxidation of the layer and formation of the nano-objects explains also layer thinning during the UV photo-ageing.

 

 

                      0% UV loss (0h)77%                                                          UV loss (1457h)


 

Fig.3: SEM SE images (10 µm) of Si-PCPDTBT: PC70BM blend layers before 0% (left) and after the degradation resulting in 77% of UV loss (right)

Acknowledgements

The work leading to this invention has received funding from the European Union Seventh Framework Programme (FP7/2011 under grant agreement ESTABLIS n° 290022) and the work was supported by the Slovak Research and Development Agency project APVV-0424-10 and projects VEGA 1/0907/13 and 1/0921/13.