Low temperature microscopy of organic optoelectronic materials

We present a report on a new capability for low temperature microscopy of organic optoelectronic semiconductor materials. We may now perform photoluminescence (PL) and conductivity measurements as a function of temperature on a microscopic level. Testing confirmed the setup's ability to support microscopic measurements at pressures of 10^-6 Torr and temperatures down to 78K. Preliminary results on high performance ADT-TES-F composite materials have been obtained including PL, of single crystals as well as donor-acceptor (D/A) spincast films, and images of microscopic D/A domains under 60-100X magnification. An increase in PL was observed with decreasing temperature in single crystals of ADT-TES-F due to a decrease in thermally activated non-radiative recombination. Microscopic images of spincast D/A composites have yielded evidence of exciplex formation at the grain boundaries, indicative of the presence of charge transfer states in these regions

Enhanced Charge Photogeneration Promoted by Crystallinity in Small-Molecule Donor-Acceptor Bulk Heterojunctions

We examined sub-nanosecond time-scale charge carrier dynamics in crystalline films of a functionalized anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene acceptor added at 7–10 wt. % concentrations, whereas a gradual decrease in peak photocurrent amplitude with acceptor concentration was observed with functionalized pentacene and indenofluorene acceptors. The results were directly correlated with the ADT-tri(ethylsilyl)ethynyl-F donor crystallinity. In the best-performing blends, the presence of crystalline acceptor domains was also established

Enhanced charge photogeneration promoted by crystallinity in small-molecule donor-acceptor bulk heterojunctions

We examined sub-nanosecond time-scale charge carrier dynamics in crystalline films of a functionalized anthradithiophene (ADT) donor (D) with three different acceptor (A) molecules. A four-fold enhancement in ultrafast charge carrier separation efficiency was observed in D/A blends with a fullerene acceptor added at 7–10 wt. % concentrations, whereas a gradual decrease in peak photocurrent amplitude with acceptor concentration was observed with functionalized pentacene and indenofluorene acceptors. The results were directly correlated with the ADT-tri(ethylsilyl)ethynyl-F donor crystallinity. In the best-performing blends, the presence of crystalline acceptor domains was also established