Effect of regioregularity and alkyl chain length on the depletion layer width formed at the interface of Al and Poly (3- Alkylthiophene) Vipul Singh 1* , Shyam S. Pandey , Wataru Takashima and Keiichi Kaneto 1 2 1 1 Graduate School of LSSE, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu-shi, Fukuoka, Japan 808-0196. Email: * vipul.lsse@gmail.com 2 Research Center for advanced Eco-fitting technology, Kyushu Institute of Technology, 2-4 Hibikino, Wakamatsu-ku, Kitakyushu-shi, Fukuoka, Japan 808-0196. 1. Introduction In this work we present bias dependent Photoluminescence (PL) based study of depletion layer formed at the Al and Poly-alkylthiophene (PAT) interface. The effect of varying the alkyl chain length (R= 4, 6, 12) as well as the regioregularity of the PAT films on the depletion layer width will be discussed in detail. 2. Experimental Methods Glass samples (for Absorption and emission spectra) having an area of 3 cm 2 were cleaned in ultrasonic bath with acetone and iso propanol. The surface of these glass samples were then made hydrophobic by silanizing with 1,1,1,3,3,3- Hexamethyldisilazane (HMDS) for 90 minutes [1]. Later these samples were spin coated with chloroform solution of PAT @ [1500 (30s), 3000 (10s)] r.p.m. For the purpose of Bias dependence PL, ITO coated glass samples were etch patterned in HCl solution using Zn dust and then were subsequently spin coated from Chloroform solution of PAT as described above, further more a 30 nm thick Top Al electrode was coated using the Physical Vapor Deposition (PVD) technique. The active cell area was found to be 40 mm 2 . Keithley 6517A electrometer was used for the bias application. PL measurements were done under ambient air conditions using Hamamatsu photonic multi channel analyzer PMA 11. A 300 mW, class 3B, He-Cd laser, 442 nm by Kimmon Electric Company was used as an optical pumping source. Thicknesses of PAT films were measured using Dektak surface profiler. 3. Results and Discussions In this work we report a novel technique of estimating the depletion layer thickness by using bias dependent PL quenching ( ) [2-5], as in eq. (1). PL Q ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ − = ) 0 ( ) ( ) 0 ( PL PL PL PL I V I I Q (1) PL emission occurs from the bulk of the semiconductor, due to the radiative decay of intermediate species called excitons. In a sandwiched cell, viz. ITO/PAT/Al, we have demonstrated a direct relationship between PL quenching and the depletion layer width as given by eq. (2), [5]. In this report we try to analyze the effect of Regioregularity and the alkyl chain length on the depletion layer width. PL Q ) (v W B BQ B A A W V W PL 2 4 ) 2 ( ln 1 ) ( 2 0 + + + − + = α (2) Figure 1 shows the absorption spectra of PAT Films (R= 4, 6, 12). It was observed that the absorption peak was slightly red shifted for PAT 6 and PAT 12 films. Also the emergence of shoulder peaks with increasing alkyl chain length suggests formation of Extended Abstracts of the 2008 International Conference on Solid State Devices and Materials, Tsukuba, 2008, -810- I-6-1 pp. 810-811