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Electrooptical Spectroscopy of Uniaxially Aligned Polythiophene Films in Field-Effect Transistors
Lee, Mi Jung,Chen, Zhuoying,Pietro, Riccardo di,Heeney, Martin,Sirringhaus, Henning American Chemical Society 2013 Chemistry of materials Vol.25 No.10
<P>Charge carriers induced in field-effect transistors based on a uniaxially aligned polythiophene polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), are investigated by electrooptical charge modulation spectroscopy (CMS). We used a zone-casting deposition method for uniaxial alignment of the nanoribbon crystalline domains of the polymer and examined the optical anisotropy of neutral and charge induced absorptions in FETs. We find that the charge-induced optical absorptions of the polaronic carriers at the interface exhibit a similar degree of uniaxial anisotropy as the absorption spectrum of the neutral polymer bulk suggesting similar degree of polymer alignment at the interface compared with the bulk. We observe subtle differences in the spectral shape of the polaron absorption polarized along and perpendicular to the polymer chain direction. We also detect an additional charge-induced absorption peak appearing at high charge carrier concentrations, which is similar to the charge-induced absorption that is typical for chemically doped films. These observations provide important insight into the interplay between polaron transport and polymer microstructure.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2013/cmatex.2013.25.issue-10/cm400266h/production/images/medium/cm-2013-00266h_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm400266h'>ACS Electronic Supporting Info</A></P>
Polaron Localization at Interfaces in High-Mobility Microcrystalline Conjugated Polymers
Zhao, N.,Noh, Y.-Y.,Chang, J.-F.,Heeney, M.,McCulloch, I.,Sirringhaus, H. WILEY-VCH Verlag 2009 ADVANCED MATERIALS Vol.21 No.37
<B>Graphic Abstract</B> <P>The charge-induced optical absorptions of two-dimensional polarons in semicrystalline, high-mobility conjugated polymers are investigated as a function of distance from an interface with polymer gate dielectrics of different dielectric constants. For high-k dielectrics, polarons in the accumulation layer at the interface are found to be more localized than those in the bulk. <img src='wiley_img/09359648-2009-21-37-ADMA200900326-content.gif' alt='wiley_img/09359648-2009-21-37-ADMA200900326-content'> </P>
Patra, Dhananjaya,Lee, Jaehyuk,Lee, Jongbok,Sredojevic, Dusan N.,White, Andrew J. P.,Bazzi, Hassan S.,Brothers, Edward N.,Heeney, Martin,Fang, Lei,Yoon, Myung-Han,Al-Hashimi, Mohammed The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.9
<P>New low band gap copolymers P1-P4, based on thienylenevinylene (TV) and pyrrolo[3,2-d:4,5-d']bisthiazole (PBTz) units composed of different alkyl side chains, such as 2-octyldodecyl (OD), n-hexadecyl (HD), 2-ethylhexyl (EH), and 9-heptadecyl (HD) groups, respectively, have been synthesized and characterized. Electrochemical and optical studies of the copolymers indicated low energy band gaps in the range of 1.40-1.47 eV. Moreover, theoretical calculation with density functional theory (DFT) and time-dependent DFT calculations demonstrated that the energy band gaps, HOMO energy levels and maximum absorption values in the copolymers were in good agreement with the experimental results. The decomposition temperature of all copolymers was measured to be above 340 degrees C by thermogravimetric analysis (TGA), which indicates high thermal stability. Thermally annealed OTFT devices based on P1-P4 thin films demonstrated a range of hole mobilities; thus, the P2 based OTFT device exhibited the highest hole mobility of 0.062 cm(2) V-1 s(-1).</P>
Du, Tian,Xu, Weidong,Daboczi, Matyas,Kim, Jinhyun,Xu, Shengda,Lin, Chieh-Ting,Kang, Hongkyu,Lee, Kwanghee,Heeney, Martin J.,Kim, Ji-Seon,Durrant, James R.,McLachlan, Martyn A. The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.32
<P>Doping is a widely implemented strategy for enhancing the inherent electronic properties of charge transport layers in photovoltaic (PV) devices. Here, in direct contrast to existing understanding, we find that a reduction in p-doping of the organic hole transport layer (HTL) leads to substantial improvements in PV performance in planar p-i-n perovskite solar cells (PSCs), driven by improvements in open circuit voltage (<I>V</I>OC). Employing a range of transient and steady state characterisation tools, we find that the improvements of <I>V</I>OC correlate with reduced surface recombination losses in less p-doped HTLs. A simple device model including screening of bulk electric fields in the perovskite layer is used to explain this observation. In particular, photoluminescence (PL) emission of complete solar cells shows that efficient performance is correlated to a high PL intensity at open circuit and a low PL intensity at short circuit. We conclude that desirable transport layers for p-i-n PSCs should be charge selective contacts with low doping densities.</P>