Alternating Copolymers Containing Bithiophene and Dialkoxynaphthalene for the Applications to Field Effect Transistor and Photovoltaic Cell: Performance and Stability

Abstract

Poly(5′,5′′-bithiophene-alt-2,6-[(1,5-didecyloxy)naphthalene]) (PBDN) was synthesized from 2,6-dibromo-l,5-didecyloxynaphthalene and 1,1′-[2,2′-bithiophene]-5,5′-diylbis[1,1,1-trimethylstannane] and was used as the active layer in organic thin-film transistors (OTFTs) and organic photovoltaic cells (OPVs). The obtained PBDN was soluble in organic solvents such as chloroform, chlorobenzene, and toluene and had a weight-averaged molecular weight of 9100, with a polydispersity index of 1.31. The photoluminescence (PL) maximum of the polymer was found at 500 and 530 nm in solution and at 567 nm in the film state, respectively. The highest occupied molecular orbital (HOMO) level of PBDN was low (−5.38 eV, ultraviolet photoemission spectroscopy and cyclic voltammetry), and the solution-processed thin-film transistors (TFTs) prepared using this polymer only showed a minimal change in their performance (<15%) after air exposure for three months, thereby retaining a field-effect-transistor (FET) mobility of 0.02 cm2/(V s). This excellent air stability is superior to those of other solution-processed polymer-based OTFTs. Analysis of the thin-film structure by in situ grazing-incidence X-ray diffraction, near-edge X-ray absorption fine structure spectroscopy, and atomic force microscopy showed that not only the low HOMO level of PBDN but also the presence of close-packed frustrated structures in the polymer film were responsible for the superior stability of the devices. Photovoltaic performances of PBDN were also presented with a high open circuit voltage of 0.83 V and power conversion efficiency of 1.3% when blended with [6,6]-phenyl-C61-butyric acid methyl ester.

Synthesis of triarylamine-based alternating copolymers for polymeric solar cell

“…Intriguingly, the copolymers exhibited low HOMO levels, which allow PSCs to have high V oc [63]. Compared with previous polymer systems composed of electron-rich triphenylamine and electron-deficient BT derivatives, such low HOMO levels of copolymers may be originated from the naphthalene unit introduced into the triarylamine [36,41,44,45].…”

“…1. Replacement of the phenyl rings of the triphenylamine with other aromatic rings such as naphthalene could be a quite efficient method to control the energy level of the copolymer, and Kwon group has reported incorporation of naphthyl groups lowers the HOMO energy level of the copolymers and increase V oc of the solar cell devices [35,44,45]. From this point of view, we introduced two (2-ethylhexyloxy)-naphthyl groups to the triarylamine moiety to render solubility of the copolymer and further control the HOMO energy level and V oc .…”

Dialkoxynaphthalene as an electron-rich unit for high-performance polymer solar cells with large open circuit voltages

“…Surprisingly, dialkoxylnaphthalene-based copolymers are seldom explored, and their photovoltaic performances are inferior to those of many D-A copolymers [21e24]. For example, the first alternating copolymer based on bithiophene and didecyloxynaphthalene was demonstrated to exhibit an open circuit voltage (V oc ) of 0.83 V and a power conversion efficiency (PCE) of 1.3% when blended with [6,6]-phenyl-C61-butyric acid methyl ester [21]. Later on, Kwon et al developed two alternating copolymers based on the didecyloxynaphthalene and 2,3-bis-(thiophene-2-yl)acrylronitrile.…”

Poly(1,4-bis((E)-2-(3-dodecylthiophen-2-yl)vinyl)benzene) for Solution Processable Organic Thin Film Transistor

“…[1][2][3][4][5][6][7][8][9][10][11][12] OTFTs based on solution-processable organic semiconductors have been increasingly investigated for use in low-cost memory devices, large-area display devices, and flexible electronic devices. [13][14][15][16] Especially, easy solution-processable polymeric semiconductors can be deposited using low-cost solution processing methods such as spin-coating, ink-jet printing, and gravure printing.…”

“…4 However, because P3HT have relatively low ionization potential (4.98 eV), 17 its TFT performances can be easily degraded by oxidative doping in air. 8 Recently, Ackermann et al reported oligothiophenes end-capped with styryl and divinylbenzene end-capped with oligothiophenes, which showed high fieldeffect mobility with high stability. 18,19 Our group also reported small fused acenes containing divinylbenzene which showed not only good mobilities but also good oxidation stability.…”