Anthracene Based Conjugated Polymers: Correlation between π-π-Stacking Ability, Photophysical Properties, Charge Carrier Mobility, and Photovoltaic Performance

This article reports on the synthesis, characterization and properties of a series of anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene)s (PPE-PPV) copolymers with general constitutional unit (Ph-C equivalent to Canthr-C equivalent to C-Ph-CH=CH-Ph-CH=CH)(n) denoted AnE-PV. Solely linear (AnE-PVaa, -ad, ae) and solely branched (AnE-PVbb) as well as mixed linear and branched (AnE-PVab, -ac, -ba, -cc) alkoxy side chains were grafted to the backbone in order to tune the pi-pi-stacking ability of the materials. It has been possible to establish a correlation between pi-pi-stacking ability, absorptive behavior, charge carrier mobility, solar cell active layer nanoscale morphology and resulting photovoltaic performance. Solar cells energy conversion efficiencies between 0.34% and 3.14% were achieved. The best performance was achieved from AnD-PVab showing both stacking ability and highest pi-pi-stacking distance of 0.386 nm as compared to 0.380 nm for the others. Poorer performance resulted from polymers with no inclination to stack. AnE-PVba, -bb, although they exhibited the higher charge carrier mobilities. Hole mobilities range from 1.5 x 10(-5) cm(2)/V.s (AnE-PVad) tp 4.5 x 10(-4) cm(2)/V.s (AnE-PVba). An increase of the open circuit voltage from similar to 650 mV to similar to 900 mV is observed with decreasing side chain density. In case of the AnE-PVcc:PCBM (1:1) blend a 2-fold increase in solar cell efficiency (from 1% to 2%) was obtained when the active layer was spin cast from a 1:1 mixture of chlorofom:chlorobenzene instead of using chlorobenzene.