Electrical properties of the interfaces in bulk heterojunction organic solar cells investigated by electrochemical impedance spectroscopy

Enhanced solar-driven photoelectrochemical water splitting using nanoflower Au/CuO/GaN hybrid photoanodes

Harnessing solar energy for large-scale hydrogen fuel (H2) production shows promise in addressing the energy crisis and ecological degradation. This study focuses on the development of GaN-based photoelectrodes for efficient photoelectrochemical (PEC) water splitting, enabling environmentally friendly H2 production. Herein, a novel nanoflower Au/CuO/GaN hybrid structure was successfully synthesized using a combination of methods including successive ionic layer adsorption and reaction (SILAR), RF/DC sputtering, and metal-organic chemical vapour deposition (MOCVD) techniques. Structural, morphological, and optical characteristics and elemental composition of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, and energy-dispersive X-ray (EDX) spectroscopy, respectively. PEC and electrochemical impedance measurements were performed for all samples. The nanoflower Au/CuO/GaN hybrid structure exhibited the highest photocurrent density of ∼4 mA cm-2 at 1.5 V vs. RHE in a Na2SO4 electrolyte with recorded moles of H2 of about 3246 μmol h-1 cm-2. By combining these three materials in a unique structure, we achieved improved performance in the conversion of solar energy into chemical energy. The nanoflower structure provides a large surface area and promotes light absorption while the Au, CuO, and GaN components contribute to efficient charge separation and transfer. This study presents a promising strategy for advancing sustainable H2 production via efficient solar-driven water splitting.

A Novel Poly(3-hexylthiophene) Engineered Interface for Electrochemical Monitoring of Ascorbic Acid During the Occurrence of Glutamate-Induced Brain Cytotoxic Edemas

Although neuroelectrochemical sensing technology offers unique benefits for neuroscience research, its application is limited by substantial interference in complex brain environments while ensuring biosafety requirements. In this study, we introduced poly(3-hexylthiophene) (P3HT) and nitrogen-doped multiwalled carbon nanotubes (N-MWCNTs) to construct a composite membrane-modified carbon fiber microelectrode (CFME/P3HT-N-MWCNTs) for ascorbic acid (AA) detection. The microelectrode presented good linearity, selectivity, stability, antifouling, and biocompatibility and exhibited great performance for application in neuroelectrochemical sensing. Subsequently, we applied CFME/P3HT-N-MWCNTs to monitor AA release from in vitro nerve cells, ex vivo brain slices, and in vivo living rat brains and determined that glutamate can induce cell edema and AA release. We also found that glutamate activated the N-methyl-d-aspartic acid receptor, which enhanced Na⁺ and Cl^- inflow to induce osmotic stress, resulting in cytotoxic edema and ultimately AA release. This study is the first to observe the process of glutamate-induced brain cytotoxic edema with AA release and to reveal the mechanism. Our work can benefit the application of P3HT in in vivo implant microelectrode construction to monitor neurochemicals, understand the molecular basis of nervous system diseases, and discover certain biomarkers of brain diseases.

Co-La-Based Hole-Transporting Layers for Binary Organic Solar Cells with 18.82 % Efficiency

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transporting layer (HTL) in organic solar cells (OSCs), but its acidity severely reduces the stability of devices. Until now, very few HTLs were developed to replace PEDOT:PSS toward stable and high-performance OSCs. Herein, a new cobalt-lanthanum (Co-La) inorganic system was reported as HTL to show a high conversion efficiency (PCE) of 18.82 %, which is among the top PCEs in binary OSCs. Since electron-rich outer shell of La atom can interact with Co atom to form charge transfer complex, the work function and conductivity of the Co-La system could be simultaneously enhanced compared to Co or La-based HTLs. This Co-La system could also be applied into other OSCs to show high performance. All these results demonstrate that binary Co-La systems as HTL can efficiently tackle the issue in hole transporting and show powerful application in OSCs to replace PEDOT:PSS.

Anion-Doped Thickness-Insensitive Electron Transport Layer for Efficient Organic Solar Cell

In organic solar cells, interfacial materials play essential roles in charge extraction, transportation, and collection. Currently, highly efficient and thickness-insensitive interfacial materials are urgently needed in printable large area module devices. Herein, water/alcohol-soluble conjugated polyelectrolyte PFNBT-Br, with medium bandgap based on benzothiadiazole, are doped by two alkali metal sodium salts, NaH₂ PO₂ , Na₂ C₂ O₄ with different counter anions, to pursue high efficiency and thickness-insensitive electron-transport layers. Results show that the doping of electron-transport material can effectively promote the performance of the devices. Moreover, electron-transport layers doped by these salts with different counter anions show different behaviors in performances. Among which, the salt with oxalate anion C₂ O₄ ^2- (also named Ox^2- ) shows much better device performance than the salt with hypophosphite anion (H₂ PO₂ ^- ), especially under the thick film condition (e.g., 50 nm). The greatly enhanced performances of interfacial material doped by Ox^2- are due to reduced R_s between the active layer material and the electrode, reduced dark-current, improved charge transport and extraction efficiency, and decreased charge recombination for the devices at thick-film condition. These results demonstrated that n-doping could be a great potential strategy for making thickness-insensitive interfacial layers, besides, the performances can be further improved by carefully selecting salts. This article is protected by copyright. All rights reserved.

MoS2/WSe2nanohybrids for flexible paper-based photodetectors

Flexible photodetectors functionalized by transition metal dichalcogenides have attracted great attention due to their excellent photo-harvesting efficiency. However, the field of optoelectronics still requires advancement in the production of large-area, broad band and flexible photodetectors. Here we report a flexible, stable, broad band and fast photodetector based on a MoS₂/WSe₂heterostructure on ordinary photocopy paper with pencil-drawn graphite electrodes. Ultrathin MoS₂/WSe₂nanohybrids have been synthesized by an ultrahigh yield liquid-phase exfoliation technique. The thin sheets of WSe₂, and MoS₂contain two to four layers with a highly c-oriented crystalline structure. Subsequently, the photodetector was exploited under ultra-broad spectral range from 400 to 780 nm. The photodetector exhibits excellent figure of merit such as on/off ratio of the order of 10³, photoresponsivity of 124 mA W^-1and external quantum efficiency of 23.1%. Encouragingly, rise/decay time of about 0.1/0.3 s was realized, which is better than in previous reports on paper-based devices.

Synthesis and Photovoltaics of Novel 2,3,4,5-Tetrathienylthiophene-co-poly(3-hexylthiophene-2,5-diyl) Donor Polymer for Organic Solar Cell

This report focuses on the synthesis of novel 2,3,4,5-tetrathienylthiophene-co-poly(3-hexylthiophene-2,5-diyl) (TTT-co-P3HT) as a donor material for organic solar cells (OSCs). The properties of the synthesized TTT-co-P3HT were compared with those of poly(3-hexylthiophene-2,5-diyl (P3HT). The structure of TTT-co-P3HT was studied using nuclear magnetic resonance spectroscopy (NMR) and Fourier-transform infrared spectroscopy (FTIR). It was seen that TTT-co-P3HT possessed a broader electrochemical and optical band-gap as compared to P3HT. Cyclic voltammetry (CV) was used to determine lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) energy gaps of TTT-co-P3HT and P3HT were found to be 2.19 and 1.97 eV, respectively. Photoluminescence revealed that TTT-co-P3HT:PC71BM have insufficient electron/hole separation and charge transfer when compared to P3HT:PC71BM. All devices were fabricated outside a glovebox. Power conversion efficiency (PCE) of 1.15% was obtained for P3HT:PC71BM device and 0.14% was obtained for TTT-co-P3HT:PC71BM device. Further studies were done on fabricated OSCs during this work using electrochemical methods. The studies revealed that the presence of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on the surface of indium tin oxide (ITO) causes a reduction in cyclic voltammogram oxidation/reduction peak current and increases the charge transfer resistance in comparison with a bare ITO. We also examined the ITO/PEDOT:PSS electrode coated with TTT-co-P3HT:PC71BM, TTT-co-P3HT:PC71BM/ZnO, P3HT:PC71BM and P3HT:PC71BM/ZnO. The study revealed that PEDOT:PSS does not completely block electrons from active layer to reach the ITO electrode.

Synergistic effect of CdSe quantum dots (QDs) and PC61BM on ambient-air processed ZnO QDs/PCDTBT: PC61BM:CdSe QDs/MoO3 based ternary organic solar cells

This paper reports the synergistic effect of colloidal CdSe quantum dots (QDs) and PC₆₁BM on the performance of ITO/ZnO QDs/PCDTBT:PC₆₁BM:CdSe QDs/MoO₃/Ag based ternary organic solar cells (OSCs). The MoO₃ and ZnO QDs (∼2.87 nm) layers work as the transparent hole transport layer (HTL) and electron transport layer (ETL), respectively. The CdSe QDs (∼4.58 nm) are blended with PC₆₁BM:PCDTBT binary solution to improve the optical properties and charge transportation. Significant photoluminescence (PL) quenching is observed when part of the PC₆₁BM is replaced by CdSe QDs with equivalent weight in the PCDTBT. The proposed ternary OSC gives an open-circuit voltage of 854 mV, a short circuit current density of 14 mA cm^-2, fill factor of 42% and power conversion efficiency (PCE) of 5.02%. The PCE of the ternary OSC is increased by more than 38% compared to the binary OSC. This significant improvement in the performance parameters is attributed to the enhanced absorption and higher transportation of photo-generated charge carriers, as well as the increased charge dissociation due to the synergistic effect of CdSe QDs and PC₆₁BM. The external quantum efficiency is also enhanced significantly in the ternary OSC due to the better conversion of solar energy into electrical energy.

Zwitterion Nondetergent Sulfobetaine-Modified SnO2 as an Efficient Electron Transport Layer for Inverted Organic Solar Cells

Tin oxide (SnO₂) has been widely accepted as an effective electron transport layer (ETL) for optoelectronic devices because of its outstanding electro-optical properties such as its suitable band energy levels, high electron mobility, and high transparency. Here, we report a simple but effective interfacial engineering strategy to achieve highly efficient and stable inverted organic solar cells (iOSCs) via a low-temperature solution process and an SnO₂ ETL modified by zwitterion nondetergent sulfobetaine 3-(4-tert-butyl-1-pyridinio)-1-propanesulfonate (NDSB-256-4T). We found that NDSB-256-4T helps reduce the work function of SnO₂, resulting in more efficient electron extraction and transport to the cathode of iOSCs. NDSB-256-4T also passivates the defects in SnO₂, which serves as recombination centers that greatly reduce the device performance of iOSCs. In addition, NDSB-256-4T provides the better interfacial contact between SnO₂ and the active layer. Thus, a higher power conversion efficiency (PCE) and longer device stability of iOSCs are expected for a combination of SnO₂ and NDSB-256-4T than for devices based on SnO₂ only. With these enhanced interfacial properties, P3HT:PC₆₀BM-based iOSCs using SnO₂/NDSB-256-4T (0.2 mg/mL) as an ETL showed both a higher average PCE of 3.72%, which is 33% higher than devices using SnO₂ only (2.79%) and excellent device stability (over 90% of the initial PCE remained after storing 5 weeks in ambient air without encapsulation). In an extended application of the PTB7-Th:PC₇₀BM systems, we achieved an impressive average PCE of 8.22% with SnO₂/NDSB-256-4T (0.2 mg/mL) as the ETL, while devices based on SnO₂ exhibited an average PCE of only 4.45%. Thus, the use of zwitterion to modify SnO₂ ETL is a promising way to obtain both highly efficient and stable iOSCs.

Improving Performance of Nonfullerene Organic Solar Cells over 13% by Employing Silver Nanowires-Doped PEDOT:PSS Composite Interface

Ag nanowires (NWs)/PEDOT:PSS composite was prepared by a facile solution-processing method and employed as anode interface in nonfullerene organic solar cells (OSCs). In the presence of a Ag NWs (5%, v/v%)/PEDOT:PSS interfacial layer, a high-power conversion efficiency up to 13.53% was achieved based on a PBDB-T-2Cl:IT-4F photoactive layer system, much higher than the efficiency of the controlled counterpart device with pristine PEDOT:PSS as anode modifier. Simultaneous enhancements in short-circuit current and fill factor were observed, in comparison to the case of the pristine PEDOT:PSS interface, due to the improved electrical conductivity of Ag NWs/PEDOT:PSS composites accompanied by the increased work function for a better matching with the indium tin oxide counter electrode, which facilitated increased charge transfer and reduced charge recombination at the anode/photoactive interface for improved device performance. The results clearly revealed that the Ag NWs/PEDOT:PSS composite interface is beneficial to improve the charge extraction and favor the realization of highly efficient nonfullerene OSCs.

Microscopic Investigations into the Effect of Surface Treatment of Cathode and Electron Transport Layer on the Performance of Inverted Organic Solar Cells

Surface treatments of various layers in organic solar cells play a vital role in determining device characteristics. In this manuscript, we report on the influence of surface treatment of indium tin oxide (ITO) electrode and electron transport layer (ETL), ZnO, on the photovoltaic performance of inverted organic solar cells (IOSC) and their correlation with the surface chemistry and surface potential as studied using X-ray photoelectron spectroscopy (XPS) and Kelvin probe force microscopy (KPFM), using the device structure glass/ITO/ZnO/P3HT: PCBM/MoO3/(Au or Ag) (P3HT, poly(3-hexylthiophene-2,5-diyl), and PCBM, phenyl-C61-butyric acid methyl ester). Our results show that although ozonization of ITO leads to an improvement in the device power conversion efficiency, the ozonization of a subsequent ZnO layer results in a decreased performance mainly because of a decrease in the fill factor (FF). However, subsequent methanol (CH3OH) treatment of ZnO layer on an ozonized ITO electrode shows substantial improvement with device efficiencies exceeding ∼4% along with superior reproducibility of the devices. Furthermore, a detailed analysis of the surface wettability, chemistry, and surface potential using contact angle measurements, XPS, and KPFM attribute the improvements to the elimination of surface defects and the changes in the surface potential. Finally, impedance analysis suggests that methanol treatment of the ZnO layers leads to the development of a favorable nanophase structure with higher conductivity, which is otherwise indiscernible using microscopic methods.