Effect of top channel thickness in near infrared organic phototransistors with conjugated polymer gate-sensing layers

Abstract

Here, we report the thickness effect of top channel layers (CLs) on the performance of near infrared (NIR)-detecting organic phototransistors (OPTRs) with conjugated polymer gate-sensing layers (GSLs). Poly(3-hexylthiophene) (P3HT) was employed as a top CL, while poly[{2,5-bis-(2octyldodecyl)-3,6-bis-(thien-2-yl)-pyrrolo[3,4-c]pyrrole-1,4-diyl}-co-{2,2′-(2,1,3-benzothiadiazole)5,5′-diyl}] (PODTPPD-BT) was used as a GSL. The thickness of P3HT CLs was varied from 10 to 70 nm. Three different wavelengths of NIR light (λ = 780, 905, and 1000 nm) were introduced and their light intensity was fixed to 0.27 mW cm−2. Results showed that all fabricated devices exhibited typical p-channel transistor behaviors and the highest drain current in the dark was obtained at the P3HT thickness (t) of 50 nm. The NIR illumination test revealed that the NIR photoresponsivity (RC) of GSL-OPTRs could be achieved at t = 50 nm irrespective of the NIR wavelength. The maximum RC of the optimized devices (t = 50 nm) reached ca. 61% at λ = 780 nm and ca. 47% at λ = 1000 nm compared to the theoretical maximum photoresponsivity.