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Record efficiencies of OPV devices nowadays reach well above 10%. However, their organic nature makes them strongly sensitive to oxygen, light, heat and humidity.
We report on long-term stabilization by ternary blending the active layers with small amounts of stabilizing compounds of different classes of antioxidants[1,3], radical scavengers[1] and light stabilizers[2]. Lifetime testing was conducted under ISOS3-degradation conditions on bulk-heterojunction cells containing a wide selection of stabilizers. Microscopic and spectroscopic methods were applied to monitor chemical degradation over time, and the observed differences are discussed in terms of energetic trap states formation within the HOMO/LUMO gap of the photoactive material, morphological and structural changes.
Both antioxidants and UV absorbers yielded an increase of the accumulated power generation by over a factor of 3 compared to the reference devices without additive. In both cases, stability improvement was caused by significant reduction of radicals within the photoactive layer, which in turn stabilizes the performance by decreasing exciton recombination. However, stabilization mechanisms of these two classes are quite different, as reflected in the burn-in. While antioxidant-stabilized cells manifested a simultaneous increase of the burn-in period and decrease of decay magnitude, UV-absorber-stabilized cells retained the same burn-in period as the reference.
[1] Turkovic V. et al, ACS Applied Materials & Interfaces 6, p 18525 (2014); http://dx.doi.org/10.1021/am5024989
[2] Turkovic V. et al, Journal of Physics D: Applied Physics 49, p 125604 (2016); http://dx.doi.org/10.1088/0022-3727/49/12/125604
[3] Turkovic V. et al, Applied Physics A 122:255 (2016); http://dx.doi.org/10.1007/s00339-016-9758-7
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