Photoresponsivity of polymer thin-film transistors based on polyphenyleneethynylene derivative with improved hole injection

The photoresponse of polymer field-effect transistors (PFETs) based on the 2,5-bis(dibutylaminostyryl)-1,4-phenylene-b-alkyne-b-1,4-bis(2-ethylhexyl)benzene terpolymer (BAS-PPE) is investigated. BAS-PPE is a photoluminescent conducting polymer with a band gap of 2.25 eV. The BAS-PPE PFETs were fabricated using an open coplanar configuration and light is illuminated onto the top side of the PFETs with no shadowing present. A sweep of V-DS demonstrates that I-DS saturation is suppressed during illumination, which suggests that pinch-off cannot be reached since the injected photogenerated carriers continue unabated. Also, with incident light, the channel cannot be turned off, even at high positive gate biases, due to the accumulation of photogenerated carriers. A sweep of V-DS shows that BAS-PPE can act as a p-type polymer and favors hole injection and transport. A sweep of V-GS shows an increase in I-DS with different light intensities. The I-light/I-dark ratio reaches as high as about 6000 at an incident light intensity of 4 muW and a photoresponsivity of 5 mA/W is calculated. (C) 2004 American Institute of Physics.