Highly sensitive thin film polymer phototransistors

Xuhua Wang; Kamol Wasapinyokul; Wei De Tan; Ruth Rawcliffe; Alasdair J. Campbell; Donal D. C. Bradley

doi:10.1117/12.735527

13 September 2007 Highly sensitive thin film polymer phototransistors

Xuhua Wang, Kamol Wasapinyokul, Wei De Tan, Ruth Rawcliffe, Alasdair J. Campbell, Donal D. C. Bradley

Proceedings Volume 6658, Organic Field-Effect Transistors VI; 66581C (2007) https://doi.org/10.1117/12.735527
Event: Photonic Devices + Applications, 2007, San Diego, California, United States

Abstract

We report solution processed highly photosensitive thin film transistors (TFTs) based on poly(9,9-dioctylfluorene-cobithiophene) (F8T2) as an active photoconducting material. Bottom gate contact coplanar device structure on Si wafer transistors was used. The photosensitivity of the drain photocurrent was investigated for different F8T2 annealing temperatures and illumination irradiances. Transistors annealed at 280^oC show the highest drain current, approximately 8 times higher than the as-spincoated device at room temperature with a gate voltage of -40V. However, the field effect mobilities in the saturation regime for all devices at different annealing temperatures are in the same order of ~10^-4 cm²/Vs. The field effect mobilities of the transistors were not affected by illumination, but the drain photocurrent of the transistor was significantly increased and the threshold voltage was shifted towards zero bias voltage when the polymer absorbs photons. The measured maximum responsivity was ~18.5 A/W for an LED light source with a peak wavelength of 465 nm and 19 nm bandwidth at 5 μW/cm² light intensity. This is so far the highest reported for F8T2 phototransistors. The characteristics of transistors dominated by the photoconductive effect (turn-off) as well as the photovoltaic effect (turn-on) against a wide range of illumination intensities are reported.

Citation Download Citation

Xuhua Wang, Kamol Wasapinyokul, Wei De Tan, Ruth Rawcliffe, Alasdair J. Campbell, and Donal D. C. Bradley "Highly sensitive thin film polymer phototransistors", Proc. SPIE 6658, Organic Field-Effect Transistors VI, 66581C (13 September 2007); https://doi.org/10.1117/12.735527

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