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The effect of atomic substitution on the optoelectronic properties of a coplanar donor-acceptor (D-A) semiconducting polymer (SPs), prepared using cyclopentadithiophene (CDT) and 2,1,3-benzothiadiazole (BT) moieties, is investigated. By substituting a carbon atom in the BT unit with CF or C-Cl, two random D-A SPs are prepared, and their optoelectronic properties are thoroughly investigated. Density functional theory calculations demonstrate that the fluorinated polymer has a slightly smaller dihedral angle (ϴ = 0.6°) than the pristine polymer (ϴ = 1.9°) in its lowest-energy conformation, implying efficient charge transport through the coplanar backbone of the fluorinated polymer. However, the chlorinated polymer shows the lowest energy at a relatively larger dihedral angle (ϴ = 139°) due to the steric hindrance induced by bulky chlorine atoms in the backbone, thereby leading to thin-film morphology, which is unfavorable for charge transport. Consequently, the fluorinated polymer yields the highest field-effect mobility (μ) of 0.57 cm2 V-1 s-1 , slightly higher than that of the pristine polymer (μ = 0.33 cm2 V-1 s-1 ), and the extended device lifetime of organic field-effect transistors over 12 d without any encapsulation layers. The results of this study provide design guidelines for air-stable D-A SPs.

The determination of the band structure along k parallel to the chain direction demonstrates significant electronic delocalization. The small effective mass [m* = 0.106mo ] is consistent with the high measured mobility.

Small-bandgap polymer solar cells (PSCs) with a thick bulk heterojunction film of 340 nm exhibit high power conversion efficiencies of 9.40% resulting from high short-circuit current density (JSC ) of 20.07 mA cm(-2) and fill factor of 0.70. This remarkable efficiency is attributed to maximized light absorption by the thick active layer and minimized recombination by the optimized lateral and vertical morphology through the processing additive.

To achieve the broad utilization of the full functionality of graphene (GR) in devices, a transfer method should be developed that can simplify the process without leaving residue of the insulating supporting layer on the surface of GR. Furthermore, stable GR doping without the use of an insulating polymer is required. Here, a new GR transfer method that uses a popular conducting polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), is reported as a new supporting layer for the transfer of GR films that are synthesized by chemical vapor deposition. The GR/PEDOT:PSS bilayer can be directly utilized without the removal process. Therefore, this transfer method simplifies the transfer process and solves the residue problem of conventional transfer methods. The stable doping of GR films is simultaneously achieved by using the PEDOT:PSS layer. The new GR/PEDOT:PSS hybrid electrodes are fully functional in polymer solar cells and polymer light-emitting diodes, outperforming the conventionally transferred GR electrodes and indium tin oxide electrodes.

Despite the excellent work function adjustability of conjugated polyelectrolytes (CPEs), which induce a vacuum level shift via the formation of permanent dipoles at the CPE/metal electrode interface, the exact mechanism of electron injection through the CPE electron transport layer (ETL) remains unclear. In particular, understanding the ionic motion within the CPE ETLs when overcoming the sizable injection barrier is a significant challenge. Because the ionic functionality of CPEs is a key component for such functions, a rigorous analysis using highly controlled ion density (ID) in CPEs is crucial for understanding the underlying mechanism. Here, by introducing a new series of CPEs with various numbers of ionic functionalities, energy level tuning at such an interface can be determined directly by adjusting the ID in the CPEs. More importantly, these series CPEs indicate that two different mechanisms must be invoked according to the CPE thickness. The formation of permanent interfacial dipoles is critical with respect to electron injection through CPE ETL (≤ 10 nm, quantum mechanical tunneling limit), whereas electron injection through thick CPE ETL (20–30 nm) is dominated by the reorientation of the ionic side chains under a given electric field.

The most effi cient class of polymer materials (as donors) follows a push-pull molecular design that utilizes internal charge transfer (ICT) from electron-rich units to electron-defi cient moieties within the fundamental repeating unit of π -conjugated polymers ( π -CPs). [ 4–6 ] However, when push-pull π -CP donors form composites with fullerene acceptors to create BHJ active layers, undesirable phase segregation between the two components is observed on the scale of a few hundred nanometers. Because large-scale phase segregation increases the probability of exciton (electron-hole pair) recombination in the BHJ active layer due to the relatively short diffusion length of the exciton in the polymers (approximately 20 nm), [ 7 ] the PCE is drastically reduced in BHJ solar cells with large-scale phase segregation. [ 8,9 ]

A new electron deficient unit, dimethyl-2H-benzimidazole (MBI), and dihydroindeno[2,1-a]indene (ININE) moiety as electron-rich unit were coupled to synthesize the conjugated polymers containing electron donor–acceptor pair for organic photovoltaics. ININE, MBI, and thiophene (or bithiophene) units were incorporated using Stille and Suzuki polymerization to generate poly(2,7-(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydro- indeno[2,1-a]indene)-alt-5,5-(4′,7′-di-2-thienyl-2,2-dimethyl-2H-benzimidazole)) (PININEDTMBIs) (or PININEBBTMBIs). In MBI, the sulfur at 2-position of 2,1,3-benzothiadiazole (BT) unit was replaced with dialkyl-substituted carbon, whereas keeping the 1,2-quinoid form, to improve the solubility of the polymers. The field-effect hole mobility of PININEBBTMBI was 3.2 × 10−4 cm2/Vs which was improved as compared to that of PININEDTMBI (2.7 × 10−5 cm2/Vs) caused by the introduction of bithiophene units. In case of the most efficient polymer, PININEBBTMBI, the device with the configuration of indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS)/polymer:PC71BM(1:4 w/w)/Al, annealed at 100 °C for 10 min demonstrated a open circuit voltage of 0.78 V, a short-circuit current density of 6.66 mA/cm2, and a fill factor of 0.41, leading to the power conversion efficiency of 2.11%, under white-light illumination (AM 1.5 G, 100 mW/cm2). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

A new fi lm-casting method for polymer electrodes is reported, in which thickness-controlled drop-casting (TCDC), using polyaniline doped with camphorsulfonic acid (PANI:CSA) is used. By combining the advantages of conventional spin-casting and drop-casting methods, and by rigorously controlling the fi lm formation parameters, fl exible polymer electrodes with high conductivity and excellent transmittance can be produced. The PANI:CSA electrodes cast by the TCDC method exhibited constant thickness-independent conductivities of ∼ 600 S cm − 1 down to a fi lm thickness of 0.2 μ m, and a high optical transmittance of about 85% at 550 nm. Furthermore, the new casting method signifi cantly reduced the sheet resistance ( ∼ 90 Ω /square) of the PANI:CSA electrodes compared with the conventional spin-cast fi lms, enhancing the performance of the devices deposited on plastic substrates. The fl exible polymer light-emitting diode produced a brightness of 6000 cd m − 2 , and the fl exible polymer solar cell exhibited a power conversion effi ciency of 2%, both of which were much higher than those of the devices fabricated by the conventional spin-casting method.

The distribution of so-called high performance work practices (HPWPs) in South Korean manufacturing is mapped showing their relative scarcity. Contextual and institutional factors associated with the 1997–98 financial crisis are advanced to explain these findings. Nevertheless, anticipating that HPWPs are likely to improve performance, we tested several hypotheses. Employment security, teams, training, job enrichment and information sharing have a positive effect on performance; however there is no evidence of synergy. Most HPWP practices are partially mediated by worker attachment to their workplace. Government workplace reform policy, firms' business and labour utilisation strategy, and the presence of professional management contribute to performance.

By coating conjugated polyelectrolytes (CPEs) on metals, the work function (WF) of metals can be tuned by electric dipoles formed through the self-assembly of cation–anion pairs on the side chains of CPEs. Recently, it has been reported that a pertinent oxidative doping of anionic CPEs results in a reversed direction in the net electric dipoles, thereby yielding opposite WF tunability compared with pristine CPEs. However, the fundamental mechanism of this reversed WF tunability is not clearly understood. Here, through a systematic study of the relationship between the chemical structure of anionic CPEs (n-type) and the corresponding oxidation-processed CPEs (p-type), it is clearly demonstrated that radical cations are generated on the π-conjugated backbone of the n-type CPEs and strongly paired with anions on the side chains of the n-type CPEs, thereby reversing the direction of the total net electric dipoles. Furthermore, it is found that the degree of radical cation–anion coupling in the CPEs is a key factor in determining their WF tunability. It is envisioned that the results will provide a fundamental understanding of CPEs for versatile interface engineering in organic electronics.