Alexander V. Akkuratov

Assessing the outdoor photochemical stability of conjugated polymers by EPR spectroscopy

We report the first outdoor study of the intrinsic photochemical stability of a series of conjugated polymers encapsulated in an inert atmosphere and exposed to natural sunlight illumination conditions in the Negev Desert. The photoinduced aging effects resulting in the modification of the chemical structures of the materials and the appearance of persistent radical species in the samples were revealed by EPR spectroscopy. Comparing the degradation profiles normalized to the total number of absorbed photons allowed us to establish some correlations between the chemical structures of polymers (and even particular building blocks) and their photostability. Our approach may be widely used for the facile screening of many existing conjugated polymers with respect to their intrinsic photostability under outdoor solar conditions as well as for the elaboration of guidelines for designing novel promising materials for stable and efficient organic photovoltaics.

ITO modification for efficient inverted organic solar cells

We demonstrate a facile approach to designing transparent electron-collecting electrodes by depositing thin layers of medium and low work function metals on top of transparent conductive metal oxides (TCOs) such as ITO and FTO. The modified electrodes were fairly stable for months under ambient conditions and maintained their electrical characteristics. XPS spectroscopy data strongly suggested integration of the deposited metal in the TCO structure resulting in additional doping of the conducting oxide at the interface. Kelvin probe microscopy measurements revealed a significant decrease in the ITO work function after modification. Organic solar cells based on three different conjugated polymers have demonstrated state of the art performances in inverted device geometry using Mg- or Yb-modified ITO as electron collecting electrode. The simplicity of the proposed approach and the excellent ambient stability of the modified ITO electrodes allows one to expect their wide utilization in research laboratories and electronic industry.