EFFECT OF BLEND SOLVENTS ON THE STABILITY OF PTB7:PCBM-BASED SOLAR CELLS

Laura Ciammaruchi 1 Gloria Zanotti 2 Francesca Brunetti 3 Eugene A. Katz 1 Iris Visoly-Fisher 1
1Department of Solar Energy and Environmental Physics, Ben-Gurion University of the Negev, Sede Boqer Campus
2Monterotondo Scalo, CNR–ISM, Rome
3Department of Electronics Engineering, Università di Tor Vergata, Rome

Low-band-gap organic photovoltaic(OPV) reached significant photo-conversion efficiencies(PCEs) and the current research faces two fundamental challenges:combining adequate lifetime with low manufacturing impact on the environment.8.7%PCE was reported for an inverted OPV cell based on PTB7:PCBM blended in o-xylene(XY),eliminating the polluting chlorine in chlorobenzene(CB) commonly used as the blend solvent[1].Since the solvent choice determines the photo-active layer morphology hence charge carrier mobility,it may also affect the degradation patterns [2].We studied solvent-related degradation in inverted PTB7:PCBM-based cell blended in CB or XY.Optical, morphological and electrical investigations point to a solvent-driven vertical stratification in the photoactive layer,affecting the degradation mechanisms.PTB7-rich bottom layers were assumed in CB-cells,while PCBM-rich top layers were found inXY-cells.XY-cells showed superior stability compared to CB-cells during storage in the dark and exposure to natural sunlight.CB-cell degradation was demonstrated mostly by Voc decrease due to morphology coarsening,while XY-cell degradation was expressed in Jsc decrease, probably due to chemical degradation ofPTB7 at the interfaces.However,XY-cells were less stable under concentrated sunlight[3],due to the increased UV illumination intensity.The reduced stability is attributed to residual XY in the photoactive layer,which is UV-sensitive,and is enhanced by the top Ag contact which acts as a photocatalyst.We conclude that the improved morphology stability,combined with a more efficient solvent evaporation process and appropriate UV filtering,vote in favor of the use of more environmentally friendly,non-chlorinated solvents such as XY.

  1. Susanna, G., et al.,Solar Energy Materials and Solar Cells, 2015, 134: 194-198
  2. Takayuki, K., et al., Japanese Journal of Applied Physics, 2014, 53.2S: 02BE06.
  3. 3. I. Visoly-Fisher, et al., Sol. Ener. Mater. & Sol. Cells 2015, 134: 99–107








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