High-Efficiency Poly(<i>p</i>-phenylenevinylene)-Based Copolymers Containing an Oxadiazole Pendant Group for Light-Emitting Diodes

A new series of high brightness and luminance efficient poly(p-phenylenevinylene) (PPV)-based electroluminescent (EL) polymers, poly[2-{4-[5-(4-(3,7-dimethyloctyloxy)phenyl)-1,3,4-oxadiazole-2-yl]phenyloxy}-1,4-phenylenevinylene] (Oxa-PPV), poly[2-{2-((3,7-dimethyloctyl)oxy)phenoxy}-1,4-phenylenevinylene] (DMOP-PPV), and their corresponding random copolymers, poly{[2-{4-[5-(4-(3,7-dimethyloctyloxy)phenyl)-1,3,4-oxadiazole-2-yl]phenyloxy}-1,4-phenylenevinylene]-co-[2-{2-((3,7-dimethyloctyl)oxy) phenoxy}-1,4-phenylenevinylene]} (Oxa-PPV-co-DMOP-PPV), with an electron-deficient 1,3,4-oxadiazole unit on the side groups, were synthesized through the Gilch polymerization method. The newly designed and synthesized asymmetric molecular structures of Oxa-PPV, DMOP-PPV, and Oxa-PPV-co-DMOP-PPV were completely soluble in common organic solvents, and defect-free optical thin film was easily spin-coated onto the indium tin oxide (ITO) substrate. Oxa-PPV shows a high glass transition temperature (Tg), which might be an advantage for long time operation of polymer light-emitting diodes (PLEDs). Double-layer LEDs with an ITO/PEDOT/polymer/Al configuration were fabricated by using those polymers. Electrooptical properties and device performance could be adjusted by introducing the Oxa-PPV content in the copolymers. The emission colors could be tuned from green to yellowish-orange via intramolecular energy transfer. The improved device performance of Oxa-PPV over DMOP-PPV and Oxa-PPV-co-DMOP-PPV may be due to better electron injection and charge balance between holes and electrons and also efficient intramolecular energy transfer from 1,3,4-oxadiazole units to PPV backbones. The maximum brightness and the luminance efficiency of Oxa-PPV were up to 19395 cd/m2 at 14 V and 21.1 cd/A at 5930 cd/m2. The maximum luminance efficiency of Oxa-PPV is ranked the highest value among the PPV derivatives to date

Facile Approach for Diblock Codendrimers by Fusion between Fréchet Dendrons and PAMAM Dendrons

For the first time, a simple and facile approach for the synthesis of diblock codendrimers by fusion between the azide focal point functionalized Fréchet-type polyether and the propargyl focal point functionalized Tomalia-type PAMAM dendrons has been described based on click chemistry, i.e., the copper-catalyzed cycloaddition reaction between alkyne and azide

Control of Threshold Voltage for Top-Gated Ambipolar Field-Effect Transistor by Gate Buffer Layer

The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (−4.1 eV) was modified by cesium carbonate and vanadium oxide to −2.1 and −5.1 eV, respectively, which could control the flat-band voltage, leading to a remarkable shift of transfer curves in both negative and positive gate voltage directions without any side effects. One important feature is that the mobility of transistors is not very sensitive to the gate buffer layer. This method is simple but useful for electronic devices where the threshold voltage should be precisely controlled, such as ambipolar circuits, memory devices, and light-emitting device applications

Convergent Synthesis of Symmetrical and Unsymmetrical PAMAM Dendrimers

Convergent Synthesis of Symmetrical and Unsymmetrical PAMAM Dendrimer

Synthesis, Characterization, and Photovoltaic Properties of 4,8-Dithienylbenzo[1,2‑<i>b</i>:4,5‑<i>b</i>′]dithiophene-Based Donor–Acceptor Polymers with New Polymerization and 2D Conjugation Extension Pathways: A Potential Donor Building Block for High Performance and Stable Inverted Organic Solar Cells

In all the previously reported 4,8-dithienylbenzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene (DTBDT)-based π-conjugated polymers, the polymerization and two-dimensional (2D) conjugation extension pathways were through the thiophenes fused to the phenyl core of DTBDT and through the thiophenes linked to the benzene core of DTBDT, respectively (BDT-directed DTBDT). Herein, with the aim of discovering another potential way to introduce the DTBDT motif in the donor–acceptor alternating polymer structure, we first report the synthesis of three new π-conjugated polymers, <b>P1</b>, <b>P2</b>, and <b>P3</b>, with a modified DTBDT building block as a donor unit. This modification results in new polymerization and 2D conjugation extension pathways for the polymers through the thiophenes linked to the benzene core of DTBDT and through the thiophenes fused to the phenyl core of the DTBDT, respectively (dithienylbenzene-directed DTBDT). Although these modified polymerization pathways of DTBDT result in less delocalized conjugation along the dithienylbenzene direction, the optical and electrochemical properties reveal that the electron-donating property of dithienylbenzene-directed DTBDT was strong enough to generate strong intramolecular charge transfer (ICT) and maintain low-lying highest occupied molecular orbital (HOMO) energy levels (−5.21 to −5.28 eV) for high air stability. Inverted organic solar cells (IOSCs) were fabricated with the configuration of ITO/ZnO/polymer:PC₇₁BM/PEDOT:PSS/Ag. By systematic optimization of the performance of the IOSCs using polar solvent treatment, the IOSCs based on <b>P1</b>, <b>P2</b>, and <b>P3</b> displayed promising power conversion efficiencies (PCE) of 6.31, 5.65, and 7.10%, respectively, which compare well with the PCE of already reported BDT-directed DTBDT-based polymers. More importantly, the stability of the IOSCs was demonstrated by their retention of 83% PCE after ambient storage for 30 days. These study results revealed the promising potential of the proposed molecular design strategy for introducing new 2D conjugation extension and polymerization pathways for a DTBDT unit for high performance and stable IOSCs. This strategy can be applied to the judicious molecular design of new polymeric materials for achieving high PCE

Impact of Aryl End Group Engineering of Donor Polymers on the Morphology and Efficiency of Halogen-Free Solvent-Processed Nonfullerene Organic Solar Cells

End group engineering on the side chain of π-conjugated donor polymers is explored as an effective way to develop efficient photovoltaic devices. In this work, we designed and synthesized three new π-conjugated polymers (PBDT-BZ-1, PBDT-S-BZ, and PBDT-BZ-F) with terminal aryl end groups on the side chain of chlorine-substituted benzo­[1,2-b:4,5b′]­dithiophene (BDT). End group modifications showed notable changes in energy levels, dipole moments, exciton lifetimes, energy losses, and charge transport properties. Remarkably, the three new polymers paired with IT-4F (halogen-free solvent processed/toluene:DPE) displayed high power conversion efficiencies (PCEs) compared to a polymer (PBDT-Al-5) without a terminal end group (PCE of 7.32%). Interestingly, PBDT-S-BZ:IT-4F (PCE of 13.73%) showed a higher PCE than the benchmark PM7:IT-4F. The improved performance of PBDT-S-BZ well correlates with its improved charge mobility, well-interdigitated surface morphology, and high miscibility with a low Flory–Huggins interaction parameter (1.253). Thus, we successfully established a correlation between the end group engineering and bulk properties of the new polymers for realizing the high performance of halogen-free nonfullerene organic solar cells

Multifunctional Narrow Band Gap Terpolymer-Enabled High-Performance Dopant-Free Perovskite and Additive-Free Organic Solar Cells with Long-Term Stability

The optoelectronic devices endowing multifunctionality while utilizing a single low-cost material have always been challenging. For this purpose, we adopted a random ternary copolymerization strategy for designing two terpolymers, namely TP-0.8-EG and TP-0.8-TEG comprising a benzothiadiazole (BT)-benzo[1,2-b:4,5-b′]dithiophene-diketopyrrolo[3,4-c]pyrrole (A1-π-D-π-A2) backbone. The figure of merits of the narrow band gap TP-0.8-EG terpolymer include deepened frontier energy levels, high hole mobility, better film formability, enriched multifunctionality, and passivation capability. Accordingly, the suitable electronic properties of TP-0.8-EG revealed that it can function as a dopant-free hole-transporting material in perovskite solar cells (PSCs) as well as the third component in organic solar cells (OSCs). Remarkably, TP-0.8-EG outperforms by exhibiting a higher power conversion efficiency (PCE) of 20.9% over TP-0.8-TEG (PCE of 18.3%) and BT-UF (PCE of 14.6%) in dopant-free PSCs. Interestingly, TP-0.8-EG fabricated along with PM6:Y7 displayed a high PCE of 16.52% in ternary OSCs. Also, TP-0.8-EG established good device storage stabilities (85 and 83% of their initial PCEs for 1200 and 500 h) in dopant-free PSC as well as OSC devices. Notably, the devices with TP-0.8-EG showed excellent thermal and moisture stabilities. To the best of our knowledge, A1-π-D-π-A2 terpolymer performing both in PSCs and OSCs with decent efficiencies and good device stabilities is a rare scenario

Efficient Approach for Improving the Performance of Nonhalogenated Green Solvent-Processed Polymer Solar Cells via Ternary-Blend Strategy

The ternary-blend approach has the potential to enhance the power conversion efficiencies (PCEs) of polymer solar cells (PSCs) by providing complementary absorption and efficient charge generation. Unfortunately, most PSCs are processed with toxic halogenated solvents, which are harmful to human health and the environment. Herein, we report the addition of a nonfullerene electron acceptor 3,9-bis­(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis­(4-hexylphenyl)-dithieno­[2,3-<i>d</i>:2′,3′-<i>d</i>′]-<i>s</i>-indaceno­[1,2-<i>b</i>:5,6-<i>b</i>′]­dithiophene (ITIC) to a binary blend (poly­[4,8-bis­(2-(4-(2-ethylhexyloxy)­3-fluorophenyl)-5-thienyl)­benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophene-<i>alt</i>-1,3-bis­(4-octylthien-2-yl)-5-(2-ethylhexyl)­thieno­[3,4-<i>c</i>]­pyrrole-4,6-dione] (P1):[6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM), PCE = 8.07%) to produce an efficient nonhalogenated green solvent-processed ternary PSC system with a high PCE of 10.11%. The estimated wetting coefficient value (0.086) for the ternary blend suggests that ITIC could be located at the P1:PC₇₁BM interface, resulting in efficient charge generation and charge transport. In addition, the improved current density, sustained open-circuit voltage and PCE of the optimized ternary PSCs were highly correlated with their better external quantum efficiency response and flat-band potential value obtained from the Mott–Schottky analysis. In addition, the ternary PSCs also showed excellent ambient stability over 720 h. Therefore, our results demonstrate the combination of fullerene and nonfullerene acceptors in ternary blend as an efficient approach to improve the performance of eco-friendly solvent-processed PSCs with long-term stability

π‑Conjugated Polymer with Pendant Side Chains as a Dopant-Free Hole Transport Material for High-Performance Perovskite Solar Cells

Dopant-free polymeric hole transport materials (HTMs) have attracted considerable attention in perovskite solar cells (PSCs) due to their high carrier mobilities and excellent hydrophobicity. They are considered promising candidates for HTMs to replace commercial Spiro-OMeTAD to achieve long-term stability and high efficiency in PSCs. In this study, we developed BDT-TA-BTASi, a conjugated donor−π–acceptor polymeric HTM. The donor benzo[1,2-b:4,5-b′]dithiophene (BDT) and acceptor benzotriazole (BTA) incorporated pendant siloxane, and alkyl side chains led to high hole mobility and solubility. In addition, BDT-TA-BTASi can effectively passivate the perovskite layer and markedly decrease the trap density. Based on these advantages, dopant-free BDT-TA-BTASi-based PSCs achieved an efficiency of over 21.5%. Furthermore, dopant-free BDT-TA-BTASi-based devices not only exhibited good stability in N2 (retaining 92% of the initial efficiency after 1000 h) but also showed good stability at high-temperature (60 °C) and -humidity conditions (80 ± 10%) (retaining 92 and 82% of the initial efficiency after 400 h). These results demonstrate that BDT-TA-BTASi is a promising HTM, and the study provides guidance on dopant-free polymeric HTMs to achieve high-performance PSCs

Highly Sensitive and Durable Organic Photodiodes Based on Long-Term Storable NiO_<i>x</i> Nanoparticles

Organic optoelectronic devices that can be fabricated at low cost have attracted considerable attention because they can absorb light over a wide frequency range and have high conversion efficiency, as well as being lightweight and flexible. Moreover, their performance can be significantly affected by the choice of the charge-selective interlayer material. Nonstoichiometric nickel oxide (NiOx) is an excellent material for the hole-transporting layer (HTL) of organic optoelectronic devices because of the good alignment of its valence band position with the highest occupied molecular orbital level of many p-type polymers. Herein, we report a simple low-temperature process for the synthesis of NiOx nanoparticles (NPs) that can be well dispersed in solution for long-term storage and easily used to form thin NiOx NP layers. NiOx NP-based organic photodiode (OPD) devices demonstrated high specific detectivity (D*) values of 1012–1013 jones under various light intensities and negative biases. The D* value of the NiOx NP-based OPD device was 4 times higher than that of a conventional poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS)-based device, an enhancement that originated mainly from the 16 times decreased leakage current. The NiOx NP-based OPD device demonstrated better reliability over a wide range of light intensities and operational biases in comparison to a device with a conventional sol–gel-processed NiOx film. More importantly, the NiOx NP-based OPD showed long-term device stability superior to those of the PEDOT:PSS and sol–gel-processed NiOx-based devices. We highlight that our low-temperature solution-processable NiOx NP-based HTL could become a crucial component in the fabrication of stable high-performance OPDs