Synthesis and Photovoltaic Properties of New Low Bandgap Isoindigo-Based Conjugated Polymers

A series of new isoindigo-based low banbap polymers, containing thiophene, thieno[3,2-b]thiophene and benzo[1,2-b:4,5-b′]dithiophene as donors, have been synthesized by Stille cross-coupling reaction. Their photophysical, electrochemical and photovoltaic properties have been investigated. These new polymers exhibit broad and strong absorption between 400 and 800 nm with absorption maxima around 700 nm. The HOMO energy levels of polymers vary between −5.20 and −5.49 eV and the LUMO energy levels range from −3.66 to −3.91 eV. The optical bandgaps of the polymers are optimized for solar cell applications and they are at about 1.5 eV. Polymer solar cells (PSC) based on these new polymers were fabricated with device structures of ITO/PEDOT:PSS/polymers: PC71BM (1:2, w/w)/LiF/Al. The photovoltaic properties of the polymers have been evaluated under AM 1.5G illumination at 100 mW/cm2 with a solar simulator. The combination of broad absorption, optimal bandgap and well matched energy levels with those of PCBMs makes these isoindigo-based low bandbap polymers promising materials for photovoltaic applications

Phosphonate-Functionalized Donor Polymer as an Underlying Interlayer To Improve Active Layer Morphology in Polymer Solar Cells

A novel polymer is developed and used as underlying interlayer to improve donor polymer/acceptor material blend morphology of active layer in polymer solar cells (PSCs). The polymer poly­{<i>N</i>-9-[1,17-bis­(diethylphosphonate)­heptadecanyl]-2,7-carbazole-<i>alt</i>-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)} (PCDTBT-Pho) is designed by attaching polar phosphonate moieties to the side chain of the donor polymer, poly­[<i>N</i>-9-heptadecanyl-2,7-carbazole-<i>alt</i>-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT). The pendant phosphonate moieties lead to different solubility and proper surface energy of PCDTBT-Pho. As a result, in PSC devices, the underlying PCDTBT-Pho layer facilitates the formation of biscontinuous network morphology in the active layer, makes the donor polymer enriched at the anode side, and induces the donor polymer to crystallize. These improvements contribute to improved charge separation and transport, leading to short-circuit current density enhancement by 12% and power conversion efficiency enhancement by 8% of the PSC devices. Thus, the design and application of PCDTBT-Pho indicate a novel approach to optimize active layer morphology and improve photovoltaic efficiency of PSCs

Gait dynamics of participants during the five walking conditions (NC = no cue; AC = auditory cue; VC = visual cue; TC = tactile cue; 3C = three cues).

<p>(a) gait speed; (b) mean stride intervals; (c) stride interval variability; and (d) scaling exponents. Error bars denote standard deviation in each case.</p

Examination of stepping response, i.e., how well each cue was followed in terms of mean residuals for the four cued conditions (AC = auditory cue; VC = visual cue; TC = tactile cue; 3C = three cues).

<p>(a) mean residuals (ms); (b) median residuals (ms); and (c) standard error (ms). A negative value means that participants walked ahead of the metronomic beat. Error bars denote standard deviation in each case.</p

Long and short Lyapunov exponents for the five walking conditions (NC = no cue; AC = auditory cue; VC = visual cue; TC = tactile cue; 3C = three cues).

<p>(a) in the AP direction; (b) in the ML direction; (c) in the VT direction; (d) in the AP direction; (e) in the ML direction; and (f) in the VT direction. Error bars denote standard deviation in each case.</p

Performance Enhancement of Polymer Light-Emitting Diodes by Using Ultrathin Fluorinated Polyimide Modifying the Surface of Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)

Herein, an insulating fluorinated polyimide (F−PI) is utilized as an ultrathin buffer layer of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in polymer light-emitting diodes to enhance the device performance. The selective solubility of F−PI in common solvents avoids typical intermixing interfacial problems during the sequential multilayer spin-coating process. Compared to the control device, the F−PI modification causes the luminous and power efficiencies of the devices to be increased by a factor of 1.1 and 4.7, respectively, along with almost 3-fold device lifetime enhancement. Photovoltaic measurement, single-hole devices, and X-ray photoelectron spectroscopy are utilized to investigate the underlying mechanisms, and it is found that the hole injection barrier is lowered owing to the interactions between the PEDOT:PSS and F−PI. The F−PI modified PEDOT:PSS layer demonstrates step-up ionization potential profiles from the intrinsic bulk PEDOT:PSS side toward the F−PI-modified PEDOT:PSS surface, which facilitate the hole injection. Moreover, the insulating F−PI layer at the PEDOT:PSS surface is also favorable for the hole injection by blocking the electrons and strengthening the local electric field at the interface

Transition-Metal-Free Synthesis of Aryl Trifluoromethyl Thioethers through Indirect Trifluoromethylthiolation of Sodium Arylsulfinate with TMSCF₃

Herein, we report an indirect trifluoromethylthiolation of sodium arylsulfinates. This transition-metal-free reaction significantly provides an environmentally friendly and practical synthetic method for aryl trifluoromethyl thioethers using commercial Ruppert–Prakash reagent TMSCF3. This approach is also a potential alternative to the current industrial production method owing to facile substrates, excellent functional group compatibility, and operational simplicity

Image_1_Insight Into the Role of PC71BM on Enhancing the Photovoltaic Performance of Ternary Organic Solar Cells.PDF

<p>The development of non-fullerene acceptor molecules have remarkably boosted power conversion efficiency (PCE) of polymer solar cells (PSCs) due to the improved spectral coverage and reduced energy loss. An introduction of fullerene molecules into the non-fullerene acceptor-based blend may further improve the photovoltaic performance of the resultant ternary PSCs. However, the underlying mechanism is still debatable. Herein, the ternary PSCs based on PBDB-T:ITIC:PC₇₁BM blend were fabricated and its PCE was increased to 10.2% compared to 9.2% for the binary PBDB-T:ITIC devices and 8.1% for the PBDB-T:PC₇₁BM PSCs. Systematic investigation was carried out to disclose the effect of PC₇₁BM on the blend morphology and charge transport behavior. It is found that the PC₇₁BM tends to intermix with the PBDB-T donor compared to the ITIC counterpart. A small amount of PC₇₁BM in the ternary blend is helpful for ITIC to aggregate and form efficient electron-transport pathways. Accordingly, the electron mobility is increased and the density of electron traps is decreased in the ternary blend in comparison with the PBDB-T:ITIC blend. Finally, the suppressed bimolecular recombination and enhanced charge collection lead to high PCE for the ternary solar cells.</p

Table_1_Insight Into the Role of PC71BM on Enhancing the Photovoltaic Performance of Ternary Organic Solar Cells.PDF

<p>The development of non-fullerene acceptor molecules have remarkably boosted power conversion efficiency (PCE) of polymer solar cells (PSCs) due to the improved spectral coverage and reduced energy loss. An introduction of fullerene molecules into the non-fullerene acceptor-based blend may further improve the photovoltaic performance of the resultant ternary PSCs. However, the underlying mechanism is still debatable. Herein, the ternary PSCs based on PBDB-T:ITIC:PC₇₁BM blend were fabricated and its PCE was increased to 10.2% compared to 9.2% for the binary PBDB-T:ITIC devices and 8.1% for the PBDB-T:PC₇₁BM PSCs. Systematic investigation was carried out to disclose the effect of PC₇₁BM on the blend morphology and charge transport behavior. It is found that the PC₇₁BM tends to intermix with the PBDB-T donor compared to the ITIC counterpart. A small amount of PC₇₁BM in the ternary blend is helpful for ITIC to aggregate and form efficient electron-transport pathways. Accordingly, the electron mobility is increased and the density of electron traps is decreased in the ternary blend in comparison with the PBDB-T:ITIC blend. Finally, the suppressed bimolecular recombination and enhanced charge collection lead to high PCE for the ternary solar cells.</p

Table_2_Insight Into the Role of PC71BM on Enhancing the Photovoltaic Performance of Ternary Organic Solar Cells.PDF

<p>The development of non-fullerene acceptor molecules have remarkably boosted power conversion efficiency (PCE) of polymer solar cells (PSCs) due to the improved spectral coverage and reduced energy loss. An introduction of fullerene molecules into the non-fullerene acceptor-based blend may further improve the photovoltaic performance of the resultant ternary PSCs. However, the underlying mechanism is still debatable. Herein, the ternary PSCs based on PBDB-T:ITIC:PC₇₁BM blend were fabricated and its PCE was increased to 10.2% compared to 9.2% for the binary PBDB-T:ITIC devices and 8.1% for the PBDB-T:PC₇₁BM PSCs. Systematic investigation was carried out to disclose the effect of PC₇₁BM on the blend morphology and charge transport behavior. It is found that the PC₇₁BM tends to intermix with the PBDB-T donor compared to the ITIC counterpart. A small amount of PC₇₁BM in the ternary blend is helpful for ITIC to aggregate and form efficient electron-transport pathways. Accordingly, the electron mobility is increased and the density of electron traps is decreased in the ternary blend in comparison with the PBDB-T:ITIC blend. Finally, the suppressed bimolecular recombination and enhanced charge collection lead to high PCE for the ternary solar cells.</p