Polymer solar cells with enhanced lifetime by improved electrode stability and sealing

Charge carrier extracting electrodes are shown to control the long term stability of state-of-the-art polymer solar cells. Especially low work function metals like aluminum as electron extracting contact and their interface to the photoactive material are identified to be very unstable due to oxidation and delamination, even under superior sealing conditions. In this study we deliberately employed a solution processible titanium oxide interlayer between the photoactive layer and the electron transporting metal contact to study the impact of this layer, in combination with a variation of metal back electrodes and different sealing conditions on overall device long term stability. An automated lifetime testing setup for in-situ IV-characterization and different imaging techniques, namely lock-in thermography and luminescence imaging, were used for investigation of time dependent photovoltaic behavior and laterally resolved degradation features. A titanium oxide/aluminum bilayer as electron extracting contact revealed to be very stable, exhibiting similar to 100 h of lifetime without any sealing and approximately 18,000 h extrapolated operation time with superior glass-glass sealing, reaching commercially usable dimensions of device stability. (C) 2013 Elsevier B.V. All rights reserved.