Electrochemical Formation of Ionic Porous Organic Polymers Based on Viologen for Electrochromic Applications

The systematic study of two ionic porous organic polymers (iPOPs) based on viologens and their first applications in the electrochromic field are reported. The viologen-based iPOPs are synthesized by electrochemical polymerization with cyano groups, providing a simple and controllable method for iPOPs that solves the film preparation problems common to viologens. After the characterization of these iPOPs, a detailed study of their electrochromic properties is conducted. The iPOP films based on viologens structure exhibit excellent electrochromic properties. In addition, the resulting iPOP films show high sensitivity to electrolyte ions of different sizes in the redox process. Electrochemical and electrochromic data of the iPOPs explain this phenomenon in detail. These results demonstrate that iPOPs of this type are ideal candidates as electrochromic materials due to their inherent porous structures and ion-rich properties.

The effect of PbS quantum dots on molecular dynamics and conductivity of PTB7:PC71BM bulk heterojunction as revealed by dielectric spectroscopy

A ternary photovoltaic blend containing the PTB7 donor component, the PC71BM acceptor component, and colloidal quantum dots of lead sulfide (PbS QDs) was investigated using broadband dielectric spectroscopy. In the dielectric loss spectrum of PTB7:PC71BM:PbS QDs, γ- and β-relaxation processes in PTB7 were recognized and analyzed in terms of Arrhenius-type equations. To elucidate the effect of PbS QDs on molecular dynamics of PTB7, the activation energies of both processes were evaluated and compared with those obtained for the binary PTB7:PC71BM blend. Using the CELIV method, the charge carrier mobility was estimated. The PbS QD incorporation into the binary blend was shown to decrease both electron and hole mobility in the ternary PTB7:PC71BM:PbS QD blend. For evaluating the charge carrier lifetime in the ternary blend, the Cole-Cole diagrams derived from the dc conductivity data were plotted. The charge carrier lifetime was found to be much less than the hole extraction time, thus providing effective accumulation of charge carries at the electrodes in the ternary blend under investigation.

Colorless to Multicolored, Fast Switching, and Highly Stable Electrochromic Devices Based on Thermally Cross-Linking Copolymer

Transparent-to-colored electrochromic devices exhibit promising application prospects and have gained popularity. Herein, two triphenylamine derivatives TPA-OCH₃ and TPA-CN with styryl moieties and different donor or acceptor units were designed and synthesized to further prepare solvent-resistant thermally cross-linking polymer P(TPA-OCH₃) and P(TPA-CN) without any additional initiator. P(TPA-OCH₃) and P(TPA-CN) possess two pairs of redox peaks, and P(TPA-OCH₃) shows a lower onset oxidation potential compared to P(TPA-CN) because of the pendent donor unit. Correspondingly, both polymers exhibit multicolored changes from the neutral colorless state to noticeable oxidized colors under different potentials. Furthermore, the thermally cross-linking copolymer P(TPA-OCH₃-co-TPA-CN) was obtained by TPA-OCH₃ and TPA-CN (the molar ratio is 2:1) and presents outstanding electrochromism with four color changes (colorless-orange-blue-purple) due to the multistep redox process of TPA-OCH₃ and TPA-CN units. It is more intriguing that the electrochromic device based on the copolymer films possesses a high optical contrast of 57.8% at 680 nm, fast switching time (0.52 and 0.66 s), and robust cyclic stability over 30 000 cycles with very little decay. Therefore, the thermally cross-linking copolymer is a promising candidate material for high-performance transmittive electrochromic devices, such as smart windows, sunglasses, and E-papers.

Copper Iodide Interlayer for Improved Charge Extraction and Stability of Inverted Perovskite Solar Cells

Nickel oxide (NiO) is one of the most promising and high-performing Hole Transporting Layer (HTL) in inverted perovskite solar cells due to ideal band alignment with perovskite absorber, wide band gap, and high mobility of charges. At the same time, however, NiO does not provide good contact and trap-free junction for hole collection. In this paper, we examine this problem by developing a double hole transport configuration with a copper iodide (CuI) interlayer for efficient surface passivation. Transient photo-current (TPC) measurements showed that Perovskite/HTL interface with CuI interlayer has an improved hole injection; CuI passivation reduces the concentration of traps and the parasitic charge accumulation that limits the flow of charges. Moreover, we found that CuI protect the HTL/perovskite interface from degradation and consequently improve the stability of the cell. The presence of CuI interlayer induces an improvement of open-circuit voltage VOC (from 1.02 V to 1.07 V), an increase of the shunt resistance RSH (100%), a reduction of the series resistance RS (-30%), and finally a +10% improvement of the solar cell efficiency.

In situ preparation and determination of electrochemical and electrochromic properties of copper phthalocyanine-polyaniline nanocomposite films

Copper phthalocyanine (CuPc) films with different morphologies were electrodeposited on the surfaces of ITO electrodes. Then, in each case, a polyaniline (PANI) film was electrochemically polymerized in situ on the surface of the copper phthalocyanine film to form a CuPc-PANI composite film. The electrochemical properties of the CuPc-PANI composite film were observed to be much better than those of the film without CuPc. With the modification involving the CuPc nanowires, the composite film formed a finer particle surface and an increased interface area between the PANI and the electrolyte. Compared to the single-component PANI film, the CuPc-PANI composite film exhibited better performance with a higher optical contrast (58% at 730 nm), a faster response speed (coloring time of 1.02 s, discoloring time of 1.96 s), and better cycling stability (68.71% of the initial electrochemical activity after 500 cycles, in contrast to only about 48.02% for PANI). Moreover, the CuPc-PANI film shows a new feature that can be used as a supercapacitor (specifically a capacitance value of about 5.4 mF cm⁻² at typical currents). Our results demonstrate that the prepared CuPc-PANI composite film is one of the best candidates for multiple potential applications such as high-performance polymer electrochromic materials and supercapacitors.

A CuPc-PANI composite film with good electrochromic properties and obvious pseudocapacitance performance was successfully prepared using in situ electrochemical methods.

Fast Switching Properties and Ion Diffusion Behavior of Polytriphenylamine Derivative with Pendent Ionic Liquid Unit

A novel triphenylamine derivative-linked ionic liquid unit, 1-(6-((4-(bis(4-(thiophen-2-yl)phenyl)amino)benzoyl)oxy)hexyl)-3-methyl-imidazolium tetrafluoroborate (TTPAC₆IL-BF₄), was designed and synthesized successfully, and its corresponding polymer PTTPAC₆IL-BF₄ was obtained by the electropolymerization method. The highest occupied molecular orbital energy band of TTPAC₆IL-BF₄ is higher and the onset oxidative potential lower compared with that of 6-bromohexyl 4-(bis(4-(thiophen-2-yl)phenyl)amino) benzoate (TTPAC₆Br) without modifying the ionic liquid unit. Both PTTPAC₆IL-BF₄ and PTTPAC₆Br show similar color change and optical contrast under different redox states. However, PTTPAC₆IL-BF₄ presents a faster electrochromic switching time than PTTPAC₆Br owing to the improved ionic conductivity and ion diffusion coefficient with the introduction of a pendent ionic liquid unit. It is more intriguing that PTTPAC₆IL-BF₄ could show electrochromism under different potentials even without supplying any additional electrolyte. The particular behavior further proves that BF₄^- ions around imidazole cations at the side chain may participate in balancing the charge of the polymer backbone when redox reaction happens, resulting in faster movement of ions during the doping process. The results imply that introducing an ionic liquid unit to the side chain is an efficient method to improve the switching time of conjugated polymers and would be inspirational for the design and preparation of novel bifunctional electrochromic polymeric electrolytes.