RESUMEN
A new zwitterionic small molecule 4-(dimethyl(pyridin-2-yl)ammonio)butane-1-sulfonate (PAS), synthesized from 2-dimethylaminopyrindine (2-DMAP), was developed for the ITO cathode modifier. PAS and 2-DMAP dissolved in methanol can form a thin layer on ITO cathode by a simple spin-coating process. The heteroatom moieties in 2-DMAP (sp2 and sp3 nitrogen) and PAS (sp2 nitrogen and sulfonate ion) can coordinate to the ITO surface and decrease the ITO work function by the induced surface dipoles. The fullerene-based (PBDTT-FTTE:PC71BM) inverted OSCs using PAS and 2-DMAP interlayer can achieve PCEs of 8.95 and 8.26%, respectively, which are superior to the devices without a modifier (PCE = 3.25%) and comparable to the corresponding ZnO-based device (PCE = 8.57%). Nevertheless, 2-DMAP, like other nitrogen-containing polymer interlayer materials, turns out to be not applicable to inverted organic solar cells (I-OSCs) with IT-4F as the n-type electron acceptor because the amino group of 2-DMAP can act as a nucleophile to attack the end-group of IT-4F at the interface. The decomposition of IT-4F by 2-DMAP was carefully proved to be via retro-aldol condensation. As a result, the device (PBDBT-F:IT-4F) modified with 2-DMAP displayed a low PCE of 7.34%. The zwitterionic PAS with reduced nucleophilicity and basicity can modify the ITO surface without decomposing IT-4F. The PBDBT-F:IT-4F-based device modified with PAS maintained a high PCE of 11.41%. Most importantly, the PAS-based device using the well-known Y6 acceptor (PBDBT-F:Y6) can achieve a PCE of 13.82%. This new interfacial material can be universally applied to I-OSCs employing various A-D-A-type acceptors installed with the electrophilic 1,1-dicyanamethylene-5,6-difluoro-3-indanone (FIC) end-group.
RESUMEN
Three unsymmetrical diiodobichalcogenophenes SSeI2, STeI2, and SeTeI2 and a diiodoterchalcogenophene SSeTeI2 were prepared. Grignard metathesis of SSeI2, STeI2, SeTeI2, and SSeTeI2 occurred regioselectively at the lighter chalcogenophene site because of its relatively lower electron density and less steric bulk. Nickel-catalyzed Kumada catalyst-transfer polycondensation of these Mg species provided a new class of side-chain regioregular and main-chain AB-type alternating poly(bichalcogenophene)s-PSSe, PSTe, and PSeTe-through a chain-growth mechanism. The ring-walking of the Ni catalyst from the lighter to the heavier chalcogenophene facilitated subsequent oxidative addition, thereby suppressing the possibility of chain-transfer or chain-termination. More significantly, the Ni catalyst could walk over the distance of three rings (ca. 1 nm)-from a thiophene unit via a selenophene unit to a tellurophene unit-to form PSSeTe, the first ABC-type regioregular and periodic poly(terchalcogenophene) comprising three different types of 3-hexylchalcogenophenes.
RESUMEN
In this research, we developed six new selenophene-incorporated naphthobisthiadiazole-based donor-acceptor polymers PNT2Th2Se-OD, PNT2Se2Th-OD, PNT4Se-OD, PNT2Th2Se-DT, PNT2Se2Th-DT, and PNT4Se-DT. The structure-property relationships have been systematically established through the comparison of their structural variations: (1) isomeric biselenophene/bithiophene arrangement between PNT2Th2Se and PNT2Se2Th polymers, (2) biselenophene/bithiophene and quarterselenophene donor units between PNT2Th2Se/PNT2Se2Th and PNT4Se polymers, and (3) side-chain modification between the 2-octyldodecylthiophene (OD)- and 2-decyltetradecyl (DT)-series polymers. The incorporation of selenophene units in the copolymers induces stronger charge transfer to improve the light-harvesting capability while maintaining the strong intermolecular interactions to preserve the intrinsic crystallinity for high carrier mobility. The organic field-effect transistor device using PNT2Th2Se-OD achieved a high hole mobility of 0.36 cm2 V-1 s-1 with an on/off ratio of 1.9 × 105. The solar cells with PNT2Th2Se-OD:PC71BM exhibited a power conversion efficiency of 9.47% with a Voc of 0.68 V, an fill factor of 67%, and an impressive Jsc of 20.69 mA cm-2.