The continuous junction (CJ) concept is a promising new design for all-polymer solar cells featuring a continuous transition from the electron donor to the acceptor material. Recent developments in the post-polymerization modification of functional polymers provide adequate chemical tools for the fabrication of CJ devices. [1][2] The current approach to the realization of CJ solar cells is to gradually invert the electronic properties of an electron-rich parent polymer using dimethyldioxirane (DMDO) as reagent during processing. Thioethers attached to the conjugated polymer backbone are selectively oxidized using DMDO. This conversion of electron-donating groups (+M effect) into electron-withdrawing sulfoxides and sulfones (-M effect) by post-polymerization modification enables an adjustment of the electronic properties depending on the added amount of the oxidation reagent. DMDO, which can be prepared on a large laboratory scale, perfectly fits the requirements for the realization of the continuous junction concept: the oxidation reaction was observed to proceed fast and selective and, most importantly, there is no reaction side-product except for volatile acetone. [3] These characteristics render a fabrication of CJ devices by the current approach particularly feasible.
[1] Glöcklhofer, F.; Lumpi, D.; Kohlstädt, M.; Yurchenko, O.; Würfel, U.; Fröhlich, J. React. Funct. Polym., 2015, 86, 16-26. [2] Glöcklhofer, F.; Lumpi, D.; Stöger, B.; Fröhlich, J. New J. Chem., 2014, 38, 2229-2232. [3] Mikula, H.; Svatunek, D.; Lumpi, D.; Glöcklhofer, F.; Hametner, C.; Fröhlich, J. Org. Process Res. Dev., 2013, 17, 313-316.