Photo-Response of Low Voltage Flexible TIPS-Pentacene Organic Field-Effect Transistors
Photo-response of solution processed flexible TIPS-pentacene organic field-effect transistors is evaluated under illumination with visible light of red, green, and blue colors having minimum wavelengths of 620, 520, and 460 nm. For −10 V operation, pristine photo-OFETs exhibited average field-effect mobility of 0.11 cm<inline-formula> <tex-math notation="LaTeX">$^{2}\text{V}^{-1}\text{s}^{-1}$ </tex-math></inline-formula>, near zero threshold voltage, and current ON–OFF ratio of ~10<sup>5</sup>. These photo-OFETs exhibited prevalent photovoltaic characteristics with shift in the threshold voltage upon illumination, which was found to increase with rising intensity, illumination time, and gate bias during illumination. For low-voltage operation at −5 V, maximum current modulation of <inline-formula> <tex-math notation="LaTeX">$4\times 10^{4}$ </tex-math></inline-formula> and 10<sup>2</sup>, and photo-responsivity of 17 mA/W and 35 mA/W, respectively, were achieved for blue (intensity of 1.7 mW/cm<sup>2</sup>) and green (intensity of 0.4 mW/cm<sup>2</sup>) light illuminations. However, these photo-OFETs did not show significant response to red light. A fast dynamic response to periodic pulses of illumination was also observed. For a gate bias of +10 V and illumination time of 500 s, maximum current modulation of 10<sup>5</sup> was achieved for blue light illumination.