Search

International audience; We have identified modifications of material distributions in inverted organic solar cell structures during accelerated aging processes that are potentially linked to the loss of the mechanical integrity of the devices. Non-encapsulated devices were treated with ISOS-D-3 ageing (the so called damp heat exposure at 85 °C/85% room humidity in the dark). After performing pull-off tests, the exposed surfaces were analyzed by X-ray photoemission spectroscopy and atomic force microscopy. For fresh devices, the results revealed that mechanical failure occurs close to the PEDOT:PSS/P3HT:PCBM interface, in agreement with the literature. However, after a short exposure to damp heat, XPS investigations indicate an enrichment of PCBM at the PEDOT:PSS/P3HT:PCBM interface and a change in the 2 PEDOT:PSS surface composition. Both phenomena may explain the rapid drop in device performances and the increased tendency towards delamination.

International audience; This work demonstrates for the first time that it is possible to prep. alternating oligomers, contg. both dyes and fullerenes in repeating structures, that act as electron acceptors in bulk heterojunction devices. A sterically controlled azomethine ylide cycloaddn. polymn. is employed with either C60 or phenyl-C61-butyric acid Me ester (PCBM) and the dye diketopyrrolopyrrole (DPP). The former results in low mol. wts. of around 5600 g mol-1, whereas the latter, PCBM, enables the formation of more sol. chains with higher mol. wts. of ca 11 200 g mol-1. Remarkably, cyclic voltammetry shows that the incorporation of PCBM into the main-chain raises the LUMO by ca 380 meV due to the in-chain bis-addns. The observation of the complete quenching of DPP fluorescence by the fullerene moiety, combined with computer modeling studies, indicates both electron and energy transfers between intra-chain moieties. Proof-of-concept devices show low efficiencies most likely due to as-yet-unoptimized prepn. and structures, but hint at the possibilities of these novel bi-functionalized, in-chain fullerenes due to their high Voc of 0.89 V with an example low-bandgap polymer, KP115, and reasonable charge mobilities of ca 1 × 10-4 cm2 V-1/s, making this new class of materials of strong interest for applications. Furthermore, their good thermal stability to above 300° and their stabilization of photovoltaic devices against thermal degrdn. confirm that this new pathway to a wide range of dye/fullerene structures is extremely promising.