Supramolecular Hemicage Cobalt Mediators for Efficient and Stable Dye-Sensitized Solar Cells
Lisa A. Fredin, Marina Freitag, Wenxing Yang, Luca D' Amario, K. Martin Karlsson, Anders Hagfeldt, Gerrit Boschloo
A new class of DSCs using the hemicage cobalt based mediator [Co(ttb)] 2+/3+ using the hexadentate ligand 5,5'',5''''-((2,4,6- triethyl highly preorganized benzene-1,3,5-triyl)tris(ethane-2,1- diyl))tri-2,2'- bipyridine (ttb) were studied. Current-voltage (I-V)characteristics were measured, incident photon to current conversion efficiency (IPCE), photoinduced absorption (PIA), and transient absorption (TAS) spectra were recorded. A 120 hours light-soaking stability test exhibited exceptionally high stability for [Co(ttb)] 3+/2+, resulting in 110% performance (compared to initial performance), as compared to 60% performance of [Co(bpy) 3 ] 3+/2+ electrolyte based DSCs under the same conditions. Photovoltaic performances were comparable for [Co(ttb)] 3+/2+ (78% IPCE, LEG4) and [Co(bpy) 3 ] 3+/2+ (73% IPCE, LEG4). The performance of the DSCs for [Co(ttb)] 3+/2+ are comparable to the conventionally used [Co(bpy) 3 ] 3+/2+ , the advantage of the hemicage complexes is within the exceptional stability under thermal and light stress.