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Accueil > Publications > 2012

Towards an understanding of light activation processes in titanium oxide based inverted organic solar cells

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The light activation phenomenon in inverted P3HT:PCBM bulk heterojunction organic solar cells
based on titanium oxide sublayer (TiOx) is characterized by fast acquisition of current-voltage
(J-V) curves under light bias as function of time. TiOx layers were thermally treated under inert
atmosphere at different temperatures prior active layer deposition and for every device an
activation time was extracted. It is shown that the higher the TiOx annealing temperature, the faster
the activation. The improvement of the overall device performances is also observed for devices
with TiOx layers baked above 100 -C. The evolution of the characteristic of the organic
semiconductors (OSC) device, from dielectric to diode, is attributed to the increase of TiOx
conductivity by three orders of magnitude upon white light illumination. Additionally, devices
based on baked TiOx present higher conductivity than those based on unbaked TiOx which would
explain the gain in performances and the short activation time of the OSC. In order to understand
the origin of the phenomenon, deactivation experiments were also performed under different
conditions on OSC. The deactivation process was shown to be thermally dependent and fully
reversible under inert atmosphere, which suggest that deep traps are responsible for the activation
phenomenon. An optimal annealing temperature was found at 120 -C and gives a reasonable short
activation time of approximately 1min and photo conversion efficiency up to 4%.