Search Results (8)

Hybrid organic–inorganic perovskite solar cells (PSCs) are receiving huge attention owing to their marvelous advantages, such as low cost, high efficiency, and superior optoelectronics characteristics. Despite their promising potential, charge-carrier dynamics at the interfaces are still ambiguous, causing carrier recombination and hindering carrier transport, thus lowering the open-circuit voltages (V_oc) of PSCs. To unveil this ambiguous phenomenon, we intensively performed various optoelectronic measurements to investigate the impact of interfacial charge-carrier dynamics of PSCs under various light intensities. This is because the charge density can exhibit different mobility and charge transport properties depending on the characteristics of the charge transport layers. We explored the influence of the hole transport layer (HTL) by investigating charge transport properties using photoluminescence (PL) and time-resolved (TRPL) to unveil interfacial recombination phenomena and optoelectronic characteristics. We specifically investigated the impact of various thicknesses of HTLs, such as 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD), and poly(triaryl)amine (PTAA), on FA_0.83MA_0.17Pb(Br_0.05I_0.95)₃ perovskite films. The HTLs are coated on perovskite film by altering the HTL’s concentration and using F4-TCNQ and 4-tert-butylpyridine (tBP) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSi) as dopants both for spiro-OMeTAD and PTAA. These HTLs diversified the charge concentration gradients in the absorption layer, thus leading to different recombination rates based on the employed laser intensities. At the same time, the generated charge carriers are rapidly transferred to the interface of the HTL/absorption layer and accumulate holes at the interface because of inefficient capacitance and mobility differences caused by differently doped HTL thicknesses. Notably, the charge concentration gradient is low at lower light intensities and did not accumulate holes at the HTL/absorption layer interface, even though they have high charge mobility. Therefore, this study highlights the importance of interfacial charge recombination and charge transport phenomena to achieve highly efficient and stable PSCs. Full article

Ionic liquid (IL) as a green solvent is entirely composed of ions; thus, it may be more than a simple solvent for ionic polymerization. Here, the cationic polymerization of p-methylstyrene (p-MeSt) initiated by 1-chloro-1-(4-methylphenyl)-ethane (p-MeStCl)/tin tetrachloride (SnCl₄) was systematically studied in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim][NTf₂]) IL at −25 °C. The results show that IL did not participate in cationic polymerization, but its ionic environment and high polarity were favorable for the polarization of initiator and monomer and facilitate the controllability. The gel permeation chromatography (GPC) trace of the poly(p-methylstyrene) (poly(p-MeSt)) changes from bimodal in dichloromethane (CH₂Cl₂) to unimodal in IL, and polydispersities M_w/M_n of the polymer in IL showed narrower (1.40–1.59). The reaction rate and heat release rate were milder in IL. The effects of the initiating system, Lewis acid concentration, and 2,6-di-tert-butylpyridine (DTBP) concentration on the polymerization were investigated. The controlled cationic polymerization initiated by p-MeStCl/SnCl₄ was obtained. The polymerization mechanism of p-MeSt in [Bmim][NTf₂] was also proposed. Full article

Methyl cellulose and its derivatives are widely used in the food industry, cosmetics, and as construction materials. The properties of methyl celluloses (MC) strongly depend on their degrees and positions of substitution. In order to generate MCs with uncommon blocky substitution, we apply fully protected O-benzyl-O-methyl celluloses (BnMC). Such complex polysaccharide derivatives could not be deprotected completely and without shift of the composition by methods usually applied to mono- and oligosaccharides. Therefore, a facile debenzylation method was developed based on photo-initiated free-radical bromination in the presence of hydrobromic acid scavengers followed by alkaline treatment. The reaction proceeds under homogeneous conditions and without the aid of any catalyst. There is no need for expensive equipment, materials, anhydrous reagents, or running the reaction under anhydrous conditions. Reaction parameters were investigated and optimized for successful debenzylation of completely protected BnMC with degrees of methyl substitution (DS_Me) around 1.9 (and DS_Bn around 1.1). Side-product-free and almost complete debenzylation was achieved when 1,2-epoxybutane (0.5 eq./eq. N-bromosuccinimide) and 2,6-di-tert-butylpyridine (0.5 eq./eq. N-bromosuccinimide) were used in the reaction. Furthermore, ATR-IR and ¹H NMR spectroscopy confirmed the successful removal of benzyl ether groups. The method was developed to monitor the transglycosylation reaction of the BnMC with permethylated cellulose, for which the deprotection of many small samples in parallel is required. This comprises the determination of the methyl pattern in the glucosyl units by gas-liquid chromatography (GLC), as well as oligosaccharide analysis by liquid chromatography mass spectrometry (LC-MS) after perdeuteromethylation and partial hydrolysis to determine the methyl pattern in the chains. The unavoidable partial chain degradation during debenzylation does not interfere with this analytical application, but, most importantly, the DS and the methyl pattern were almost congruent for the debenzylated product and the original MC, indicating the full success of this approach The presented method provides an unprecedented opportunity for high throughput and parallel debenzylation of complicated glucans, such as BnMC (as a model compound), for analytical purposes. For comparison, debenzylation using Na/NH₃ was applied to BnMC and resulted in a completely debenzylated product with a remarkably high recovery yield of 99 mol% and is, thus, the method of choice for synthetic applications, e.g., for the transglycosylation product prepared under the selected conditions in a preparative scale. Full article

An ionic liquid, 1-methyl-3-propylimidazolium iodide (MPII), was solidified with an organic hole-transporting material, 4,4′,4″-tris[(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA), and the resulting solid-state redox mediator (RM) (m-MTDATA-solidified MPII) was employed in solar devices to realize solid-state dye-sensitized solar cells (sDSSCs). Solar devices with only MPII or m-MTDATA as an RM showed almost 0 mA/cm² of short-circuit current (J_sc) and thus 0% power conversion efficiency (PCE). However, an sDSSC with the m-MTDATA-solidified MPII exhibited 4.61 mA/cm² of J_sc and 1.80% PCE. It was found that the increased J_sc and PCE were due to the formation of I₃⁻, which resulted from a reaction between the iodie (I⁻) of MPII and m-MTDATA cation. Further enhancement in both J_sc (9.43 mA/cm²) and PCE (4.20%) was observed in an sDSSC with 4-tert butylpyridine (TBP) as well as with m-MTDATA-solidified MPII. We attributed the significant increase (about 230%) in PCE to the lowered diffusion resistance of I⁻/I₃⁻ ions in the solid-state RM composed of the m-MTDATA-solidified MPII and TBP, arising from TBP’s role as a plasticizer. Full article

Dimethyl ether (DME) is considered an alternative hydrogen carrier with potential use in fuel cells and automotive and domestic applications. Dimethyl ether hydrolysis to methanol is a thermodynamically limited reaction catalyzed by solid-acid catalysts, mainly Al₂O₃ and zeolites. Moreover, it is the rate-limiting step of the DME steam reforming reaction, which is employed for the production of hydrogen fuel for fuel cell feeding. In the present study, the performance of WO₃/Al₂O₃ catalysts (0–44% wt. WO₃) was tested in DME hydrolysis reaction. The catalysts were characterized by means of N₂-physisorption, XRD, Raman spectroscopy, XPS, NH₃-TPD and 2,6-di-tert-butylpyridine adsorption experiments. The reaction rate of DME hydrolysis exhibited a volcanic trend as a function of tungsten surface density, while the best-performing catalyst was 37WO₃/Al₂O₃, with a tungsten surface density of 7.4 W/nm², noting that the theoretical monolayer coverage for the specific system is 4–5 W/nm². Brønsted acidity was directly associated with the catalytic activity, following the same volcanic trend as a function of tungsten surface density. Blocking of Brønsted acid sites with 2,6-di-tert-butylpyridine led to a dramatic decrease in hydrolysis rates by 40 times, proving that Brønsted acid sites are primarily responsible for the catalytic activity. Thus, the type and strength rather than the concentration of acid sites are the key factors influencing the catalytic activity. Full article

High-efficiency and stable hole transport materials (HTMs) play an essential role in high-performance planar perovskite solar cells (PSCs). 2,2,7,7-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobi-fluorene (Spiro-OMeTAD) is often used as HTMs in perovskite solar cells because of its excellent characteristics, such as energy level matching with perovskite, good film-forming ability, and high solubility. However, the accumulation and hydrolysis of the common additive Li-TFSI in Spiro-OMeTAD can cause voids/pinholes in the hole transport layer (HTL), which reduces the efficiency of the PSCs. In order to improve the functional characteristics of HTMs, in this work, we first used CsI as a dopant to modify the HTL and reduce the voids in the HTL. A small amount of CsI is introduced into Spiro-OMeTAD together with Li-TFSI and 4-tert-butylpyridine (TBP). It is found that CsI and TBP formed a complex, which prevented the rapid evaporation of TBP and eliminated some cracks in Spiro-OMeTAD. Moreover, the uniformly dispersed TBP inhibits the agglomeration of Li-TFSI in Spiro-OMeTAD, so that the effective oxidation reaction between Spiro-OMeTAD and air produces Spiro-OMeTAD⁺ in the oxidation state, thereby increasing the conductivity and adjusting the HTL energy. Correspondingly, the PCE of the planar PSC of the CsI-modified Spiro-OMeTAD is up to 13.31%. In contrast, the PSC without CsI modification showed a poor PCE of 10.01%. More importantly, the PSC of Spiro-OMeTAD treated with CsI has negligible hysteresis and excellent long-term stability. Our work provides a low-cost, simple, and effective method for improving the performance of hole transport materials and perovskite solar cells. Full article

Density functional theory-based molecular modeling (DFT/MM) validates that KI and I₂ undergo exothermic van der Waals (vdW) aggregation in acetonitrile (AN) or in the presence of 4-tert-butylpyridine (TBP), forming potassium triiodide (KI₃) and, further mutual vdW aggregation leads to the formation of (KI₃)₂ and AN, (KI₃)₂ and (AN)₂ and (KI₃)₂ and TBP in the AN-based Dye sensitized solar cells (DSSC) electrolytes. All KI₃ aggregates have a very low energy gap, 0.17 eV, 0.14 eV and 0.05 eV of lowest unoccupied molecular orbital (LUMO) + 1 and LUMO, respectively, verifying efficient electron diffusion in μm-thick DSSC electrolytes. Hydrogen-bonding aggregation of anatase TiO₂ model, Ti₉O₁₈H and OH, with N3 (proton) dye is also validated by DFT/MM, and the energy structure verifies unidirectional electron flow from highest occupied molecular orbital (HOMO) on thiocyanide (SCN) groups of N3 dye to LUMO on the TiO₂ model at the aggregates. Further, DFT/MM for the aggregation of K⁺I₃⁻ with N3 verifies the most exothermic formation of the aggregate of N3 (proton) and K⁺I₃⁻. The UV-Vis spectra of N3 (proton) and K⁺I₃⁻ is consistent with reported incident photocurrent efficiency (IPCE) action spectra (λ = 450–800 nm) of N3-sensitized DSSC, verifying that the N3 dye of N3 (proton) and K⁺I₃⁻ becomes an effective sensitizer in the anode / TiO₂ / N3 (proton) / KI/I₂ / acetonitrile (AN) / cathode structured DSSC. The energy structure of LUMO and LUMO + 1 of the aggregates, Ti₉O₁₈H and OH and N3 (proton), N3 and K⁺I₃⁻, (KI₃)₂ and AN and (KI₃)₂ and TBP verifies high IPCE photocurrent and effective electron diffusion via KI₃-aggregates in the DSSC of Ti₉O₁₈H and OH and N3 (proton) and K⁺I₃⁻. Full article

Organic materials have been found to be promising candidates for low-temperature thermoelectric applications. In particular, poly (3-hexylthiophene) (P3HT) has been attracting great interest due to its desirable intrinsic properties, such as excellent solution processability, chemical and thermal stability, and high field-effect mobility. However, its poor electrical conductivity has limited its application as a thermoelectric material. It is therefore important to improve the electrical conductivity of P3HT layers. In this work, we studied how molecular weight (MW) influences the thermoelectric properties of P3HT films. The films were doped with lithium bis(trifluoromethane sulfonyl) imide salt (LiTFSI) and 4-tert butylpyridine (TBP). Various P3HT layers with different MWs ranging from 21 to 94 kDa were investigated. UV–Vis spectroscopy and atomic force microscopy (AFM) analysis were performed to investigate the morphology and structure features of thin films with different MWs. The electrical conductivity initially increased when the MW increased and then decreased at the highest MW, whereas the Seebeck coefficient had a trend of reducing as the MW grew. The maximum thermoelectric power factor (1.87 μW/mK²) was obtained for MW of 77 kDa at 333 K. At this temperature, the electrical conductivity and Seebeck coefficient of this MW were 65.5 S/m and 169 μV/K, respectively. Full article