Abstract

We report a study of long-lived photo-excited states in single crystals of functionalized forms of pentacene: 6,13-bis (triisopropylsilylethynyl) pentacene, 6,13-bis (triethylsilylethynyl) pentacene, and 6,13-bis (triethylgermylethynyl) pentacene, organic semiconductors with band gaps ≈1 eV. The relaxation rates are thermally activated, as determined from time and temperature-dependent measurements of the photo-conductivity after illumination. These states can be produced in a stable population at temperatures below 150 K. Hence, after low temperature illumination, thermally stimulated current (TSC) is observed as temperature increases. Trap energies associated with these states can be estimated by analysis of the TSC signal.

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