AZO/Ag/AZO multilayer films prepared by DC magnetron sputtering for dye-sensitized solar cell application

Ag films were deposited on Al-doped ZnO (AZO) films and coated with AZO to fabricate AZO/Ag/AZO multilayer films by DC magnetron sputtering on glass substrates without heating of glass substrates. The best multilayer films have low sheet resistance of 19.8 Ω/Sq and average transmittance values of 61% in visible region. It was found that the highest figure of merit (F_TC) is 6.9 × 10⁻⁴ Ω⁻¹. For the dye-sensitized solar cell (DSSC) application, the multilayer films were used as transparent conductive electrode (multilayer films/ZnO + Eosin-Y/LiI + I₂/Pt/FTO). The best DSSC based on the multilayer films showed that open circuit voltage (V_oc) of 0.47 V, short circuit current density (J_sc) of 2.24 mA/cm², fill factor (FF) of 0.58 and incident photon-to-current conversion efficiency (η) of 0.61%. It was shown that the AZO/Ag/AZO multilayer films have potential for application in DSSC.     

使用PTB7作为阳极修饰层提高有机发光二极管的性能

采用poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b’]dithiophene-2,6-diyl][3-?uoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]](PTB7)作为有机发光二极管器件的阳极修饰层,制备了结构为indium tin oxide(ITO)/PTB7(不同浓度)/N,N’-Bis(naphthalen-1-yl)-N,N’-bis(phenyl)benzidine(NPB,40 nm)/8-hydroxyquinoline(Alq3,60 nm)/LiF(1 nm)/Al的系列器件,同时研究了不同浓度的PTB7对器件性能的影响.PTB7的最佳浓度为0.25 mg/mL,器件性能得到明显的改善,起亮电压为4.3 V.当驱动电压为14.6 V时,最大亮度为45800 cd/m2,最大电流效率为9.1 cd/A.与没有PTB7修饰的器件相比,其起亮电压降低了1.9 V,最高亮度提升了78.5%.器件性能提高归因于PTB7的插入使得空穴注入和传输能力大大改善.     

A study of electrical enhancement of polycrystalline MgZnO/ZnO bi-layer thin film transistors dependence on the thickness of ZnO layer

A polycrystalline MgZnO/ZnO bi-layer was deposited by using a RF co-magnetron sputtering method and the MgZnO/ZnO bi-layer TFTs were fabricated on the thermally oxidized silicon substrate. The performances with varying the thickness of ZnO layer were investigated. In this result, the MgZnO/ZnO bi-layer TFTs which the content of Mg is about 2.5 at % have shown the enhancement characteristics of high mobility (6.77–7.56 cm² V⁻¹ s⁻¹) and low sub-threshold swing (0.57–0.69 V decade⁻¹) compare of the ZnO single layer TFT (μ_FE = 5.38 cm² V⁻¹ s⁻¹; S.S. = 0.86 V decade⁻¹). Moreover, in the results of the positive bias stress, the ΔV_on shift (4.8 V) of MgZnO/ZnO bi-layer is the 2 V lower than ZnO single layer TFT (ΔV_on = 6.1 V). It reveals that the stability of the MgZnO/ZnO bi-layer TFT enhanced compared to that of the ZnO single layer TFT.     

Low-voltage-drive and high output current ZnO thin-film transistors with sputtering SiO2 as gate insulator

Low-voltage-drive ZnO thin-film transistors (TFTs) with room-temperature radio frequency magnetron sputtering SiO₂ as the gate insulator were fabricated successfully on the glass substrate. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 4.2 V, a field effect mobility of 11.2 cm²/V s, an on/off ratio of 3.1 × 10⁶ and a subthreshold swing of 0.61 V/dec. The drain current can reach to 1 mA while the gate voltage is only of 12 V and drain voltage of 8 V. The C–V characteristics of a MOS capacitor with the structure of ITO/SiO₂/ZnO/Al was investigated. The carrier concentration N_D in the ZnO active layer was determined, the calculated N_D is 1.81 × 10¹⁶ cm⁻³, which is the typical value of undoped ZnO film used as the channel layer for ZnO-TFT devices. The experiment results show that SiO₂ film is a promising insulator for the low voltage and high drive capability oxide TFTs.     

Overcoming the thickness paradox: Systematical optimization of inverted polymer solar cells

Inverted structure comes out to be a promising alternative for making polymer solar cells (PSC) with high efficiency and long-term stability. Vertically stacked functional layers with planar shapes often suffer contradictions in holding high optical absorption and excellent charge transfer/hindrance capability to construct well performed inverted PSC devices. Here, we give an example of rational control of the thickness of electron transport layer (ETL), hole transport layer (HTL) and organic active layer (OAL) to achieve a synergistic effect on promoting the overall photovoltaic behaviors. With in-depth exploration of the interaction between device performance and layer thickness, we obtain the optimized device ITO/ZnO Ncs (45 nm)/P3HT:PCBM (70 nm)/MoO₃ (1 nm)/Ag (70 nm) exhibiting an V_oc of 0.63 V, J_sc of 12.52 mA/cm², FF of 54% and PCE of 4.26%.     

Cu2S nanocrystals incorporated highly efficient non-fullerene ternary organic solar cells

Here, we report Cu₂S nanocrystals based non-fullerene ternary polymer solar cells by incorporating Cu₂S in conjugated polymer (PBDB-T: poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl) benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione))]) and small molecule non-fullerene compound (ITIC:3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene). The devices were fabricated in inverted configuration i.e. ITO/ZnO/PBDB-T: Cu₂S NCs: ITIC/MoO₃/Ag. Effect of concentration of Cu₂S nanocrystals on the performance parameters of PBDB-T: ITIC based organic solar cells is studied. An enhancement in the power conversion efficiency from 8.24% to 9.53% is achieved for the optimum concentration of Cu₂S nanocrystals in the organic photoactive blend. The cause of improvement in the performance parameters of the device is investigated by means of the light intensity dependent electrochemical impedance spectroscopy and atomic force microscopy. It is found that the devices with Cu₂S nanocrystals have less trap-assisted recombination.     

2,7-Carbazole and thieno[3,4-c]pyrrole-4,6-dione based copolymers with deep highest occupied molecular orbital for photovoltaic cells

Three kinds of donor–acceptor (D–A) type photovoltaic polymers were synthesized based on 2,7-carbazole and thieno[3,4-c]pyrrole-4,6-dione (TPD). The conjugation of weakly electron (e)-donating 2,7-carbazole and strongly e-accepting TPD moieties yielded a deep highest occupied molecular orbital (HOMO) and its energy level was fine-controlled to be −5.72, −5.67 and −5.57 eV through the incorporation of thiophene (T), thieno[3,2-b]thiophene (TT) and bithiophene (BT) as a π-bridge. Polymer:[6,6]-phenyl-C₇₁ butyric acid methyl ester (PC₇₁BM) based bulk heterojunction solar cells exhibited a high open-circuit voltage (V_OC) in the range, 0.86–0.94 V, suggesting good agreement with the measured HOMO levels. Despite the high V_OC, the thiophene (or thienothiophene)-containing PCTTPD (or PCTTTPD) showed poor power conversion efficiency (PCE, 1.14 and 1.25%) because of the very low short-circuit current density (J_SC). The voltage-dependent photocurrent and photoluminescence quenching measurements suggested that hole transfer from PC₇₁BM to polymer depends strongly on the HOMO level of the polymer. The PCTTPD and PCTTTPD devices suffered from electron–hole recombination at the polymer/PC₇₁BM interfaces because of the insufficient energy offset between the HOMOs of the polymer and PC₇₁BM. The PCBTTPD:PC₇₁BM device showed the best PCE of 3.42% with a V_OC and J_SC of 0.86 V and 7.79 mA cm⁻², respectively. These results show that photovoltaic polymers should be designed carefully to have a deep HOMO level for a high V_OC and sufficient energy offset for ensuring efficient hole transfer from PC₇₁BM to the polymer.     

Effects of seed layer on the structure and property of zinc oxide thin films electrochemically deposited on ITO-coated glass

ZnO films with different morphologies were deposited on the ITO-coated glass substrate from zinc nitrate aqueous solution at 65 °C by a seed-layer assisted electrochemical deposition route. The seed layers were pre-deposited galvanostatically at different current densities (i_sl) ranging from −1.30 to −3.0 mA/cm², and the subsequent ZnO films had been done using the potentiostatic technique at the cathode potential of −1.0 V. Densities of nucleation centers in the seed layers varied with increasing the current density, and the ZnO films on them showed variable morphologies and optical properties. The uniform and compact nanocrystalline ZnO film with (0 0 2) preferential orientation was obtained on seed layer that was deposited under the current density (i_sl) of −1.68 mA/cm², which exhibited good optical performances.     

Effects of compositions on properties of PEO–KI–I2 salts polymer electrolytes for DSSC

The effects of compositions on properties of PEO/KI/I₂ salts polymer electrolytes were investigated to optimize the photovoltaic performance of solid state DSSCs. XRD pattern for the mole ratio 12:1 of [EO:KI] was showed the formation of complete amorphous complex. DSC results also confirmed the amorphous nature of the polymer electrolyte. The highest value of ionic conductivity is 8.36 × 10^− 5 S/cm at 303 K (ambient temperature) and 2.32 × 10^− 4 S/cm at 333 K (moderate temperature) for the mole ratio 12:1 of EO:KI complex. The effect of contribution of [I⁻] and [I₃⁻] concentration with conductivity were also evaluated. FTIR spectrum reveals that the alkali metal cations were co-ordinated to ether oxygen of PEO. The formation of polyiodide ions, such as symmetric I₃⁻ (114 cm^− 1) and I₅⁻ (145 cm^− 1) caused by the addition of iodine was confirmed by FT Raman spectroscopic measurements. The optimum composition of PEO–KI–I₂ polymer electrolyte system for higher conductivity at ambient and moderate temperatures was reported. A linear Arrhenius type behaviour was observed for all the PEO–KI polymer complexes. Transport number measurements were carried out for several polymer electrolyte compositions. Dye-sensitized solar cells were fabricated by using higher conductivity polymer electrolyte compositions and its photoelectrochemical performance was investigated. The fill factor, short-circuit current, photovoltage and energy conversion efficiency of the DSSC assembled with optimized electrolyte composition were calculated to be 0.563, 6.124 mA/cm², 593 mV and 2.044% respectively.     

ZnO/TiO2 core–shell heterojunction for CdS and PbS quantum dot-cosensitized solar cells

ZnO nanorods (NRs) with regular morphology were prepared through hydrothermal method, and the TiO₂ shell was assembled onto the surface of ZnO NRs by spin coating to the ZnO/TiO₂ core–shell heterojunction. CdS and PbS quantum dots (QDs) were used to cosensitize the ZnO/TiO₂ nanostructure by direct adsorption (DA) and successive ionic layer adsorption and reaction, respectively. SEM, TEM, and HRTEM images show that the samples possessed a rough surface and four lattice fringes indicating the successful synthesis of the ZnO/TiO₂/CdS/PbS composite structure. The ZnO/TiO₂(10T)/CdS/PbS sample showed a high absorption intensity at a broad range of wavelength to visible light region. The ZnO/TiO₂(10T)/CdS/PbS photoelectrode with QDSSCs showed the highest IPCE of 36.04% and photoelectric efficiency (η) of 1.59%; these values increased by approximately 550% and 150% compared with those of unsensitized ZnO (0.29%) and ZnO/TiO₂(10T) (1.04%) and about 146% and 120% compared with those of ZnO/TiO₂(10T)/CdS and ZnO/TiO₂(10T)/PbS, respectively. The fill factor was 0.36, and the photocurrent density (J_sc) and open circuit voltage (V_oc) reached the maximum values of 9.73 mA cm⁻² and 0.46 V, respectively.     

Nanostructural analysis of ZnO:Al thin films for carrier-transport mechanisms

The carrier mobility of sputter-deposited Al-doped ZnO transparent-conducting (ZnO:Al) thin films was controlled between 22 and 48 cm²/Vs by varying the ZnO:Al seed layer. The statistical distribution of the [001] grain misorientation was characterized from the X-ray diffraction rocking curve in the range from 0.043 (2.5°) to 0.179 rad (10.2°). The grain-boundary energy barriers (E_b) from Seto's model [1] clearly exhibit linear dependence on the grain-boundary misorientation angle (ω) according to the equation E_b = 78 ± 4 + 173 ± 32 ω meV.     

The transparence comparison of Ga- and Al-doped ZnO thin films

The Ga-doped ZnO (GZO) and Al-doped ZnO (AZO) thin films were grown on quartz glass substrates by pulsed laser deposition under different oxygen partial pressures (PO₂). The transparent performances of films versus properties of structure and conductivity were discussed. With the increase of PO₂, the transmittance of both GZO films and AZO films increased to maximum and then decreased which were in according with the change of crystallization quality. The transmittance of GZO films was higher than that of AZO films, which were not dominated by the impurity ions induced by doping. AFM images and surface roughness mean square coefficients showed that the surfaces of GZO films were smoother than that of AZO films, which were due to the dopant Ga acting as the surfactant and smoothed the GZO films surface.     

Raman scattering investigations on Co-doped ZnO epitaxial films: Local vibration modes and defect associated ferromagnetism

Raman scattering spectroscopy has been performed on high quality Co-doped ZnO epitaxial films, which were grown on Al₂O₃ (0001) by oxygen-plasma assisted molecular beam epitaxy. Raman measurements revealed two local vibration modes (LVMs) at 723 and 699 cm⁻¹ due to the substitution of Co²⁺ in wurtzite ZnO lattice. The LVM at 723 cm⁻¹ is found to be an elemental sensitive vibration mode for Co substitution. The LVM at 699 cm⁻¹ can be attributed to enrichment of Co²⁺ bound with oxygen vacancy, the cobalt–oxygen vacancy–cobalt complexes, in Zn_1−xCo_xO films associated with ferromagnetism. The intensity of LVM at 699 cm⁻¹, as well as saturated magnetization, enhanced after the vacuum annealing and depressed after oxygen annealing.     

Bulk and surface properties of ionic salt CsH5(PO4)2

We report a comparative study of transport and thermodynamic properties of single-crystal and polycrystalline samples of the ionic salt CsH₅(PO₄)₂ possessing a peculiar three-dimensional hydrogen-bond network. The observed potential of electrolyte decomposition ≈ 1.3 V indicates that the main charge carriers in this salt are protons. However, in spite of the high proton concentration, the conductivity appears to be rather low with a high apparent activation energy E_a ≈ 2 eV, implying that protons are strongly bound. The transport anisotropy though is not large, correlates with the crystal structure: the highest conductivity is found in the [001] direction (σ_130 °C ∼ 5.6 × 10^− 6 S cm^− 1) while the minimal conductivity is in the [100] direction (σ_130 °C ∼ 10 ⁻⁶ S cm^− 1). The conductivity of polycrystalline samples appears to exceed the bulk one by 1–3 orders of magnitude with a concomitant decrease of the activation energy (E_a ≈ 1.05 eV), which indicates that a pseudo-liquid layer with a high proton mobility is formed at the surface of grains. Infrared and Raman spectroscopy used to study the dynamics of the hydrogen-bond system in single-crystal and polycrystalline samples have confirmed the formation of such a modified surface layer in the latter. However, no bulk phase transition into the superionic disordered phase is observed in CsH₅(PO₄)₂ up to the melting point T_melt ∼ 151.6 °C, in contrast to its closest relative compound CsH₂PO₄.     

Roles of Al-doped ZnO (AZO) modification layer on improving electrochemical performance of LiNi<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>O<Subscript>2</Subscript> thin film cathode

Al-doped ZnO (AZO) was sputtered on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM) thin film electrode via radio frequency magnetron sputtering, which was demonstrated to be a useful approach to enhance electrochemical performance of thin film electrode. The structure and morphology of the prepared electrodes were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy techniques. The results clearly demonstrated that NCM thin film showed a strong (104) preferred orientation and AZO was uniformly covered on the surface of NCM electrode. After 200 cycles at 50 μA μm^?1 cm^?2, the NCM/AZO-60s electrode delivered highest discharge capacity (78.1 μAh μm^?1 cm^?2) compared with that of the NCM/AZO-120s electrode (62.4 μAh μm^?1 cm^?2) and the bare NCM electrode (22.3 μAh μm^?1 cm^?2). In addition, the rate capability of the NCM/AZO-60s electrode was superior to the NCM/AZO-120s and bare NCM electrodes. The improved electrochemical performance can be ascribed to the appropriate thickness of the AZO coating layer, which not only acted as HF scavenger to keep a stable electrode/electrolyte interface but also reduced the charge transfer resistance during cycling.     

2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-based donor-acceptor type copolymers for photovoltaic cells

Alternating donor-acceptor type copolymers, poly[{5,11-di(9′-heptadecanyl)indolo[3,2-b]carbazole}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5′-diyl}] (PIC-TZ) and poly[{6,6′,12,12′-tetraoctylindeno[1,2-b]fluorene}-alt-{2,5-di(thiophen-2-yl)thiazolo[5,4-d]thiazole-5,5′-diyl}] (PIF-TZ), were synthesized and examined for applications in polymeric photovoltaic cells. The polymers have a fused coplanar main backbone with good planarity for intermolecular packing and high charge mobility. The indolocarbazole and indenofluorene units contain two or four binding sites for alkyl substituents that have pronounced solution processiblity compared to the carbazole and fluorene moieties. The number-average molecular weights (M_n) of the synthesized polymers were determined to be 11,000 g/mol (PDI = 2.27) for PIC-TZ, and 17,000 g/mol (PDI = 1.77) for PIF-TZ. The optical band gap of PIC-TZ and PIF-TZ in film was determined to be 2.14 eV and 2.21 eV, respectively, and an electrochemical study confirmed the desirable HOMO/LUMO levels of the copolymers, which enabled efficient electron transfer and a high open circuit voltage (V_OC) when blending them with fullerene derivatives. The space charge limited current mobility measurements showed a hole mobility of 10⁻³ cm² V⁻¹ s⁻¹ for the copolymers. When the polymers were blended with [6,6]phenyl-C₆₁-butyric acid methyl ester (PCBM), PIC-TZ showed the best performance with V_OC, short-circuit current and power conversion efficiency of 0.86 V, 4.16 mA/cm² and 1.64%, respectively, under AM 1.5G illumination conditions (100 mW cm⁻²).     

Comparative study on Cu2ZnSn(S,Se)4 based thin film solar cell performances by adding various back surface field (BSF) layers

In this research work, SCAPS-1D (Solar Cell Capacitance Simulator in one Dimension) is used to simulate the CZTSSe (Cu2ZnSn(S,Se)4) solar cell with Al/ZnO:Al/ZnO(i)/CdS/CZTSSe/Mo structure. The simulation results have been compared and validated with real experimental results. After that, an effective receipt is proposed with the aim of improving the efficiency of the CZTSSe solar cell, in which a BSF layer is inserted using various materials (SnS, CZTSSe and CZTSe). The obtained results show that the efficiencies of CZTSSe solar cells are increased from 12.3% to 15.7%, 15.3% and 15% by the insertion of SnS, CZTSSe and CZTSe materials as BSF layers, respectively. This enhancement corresponds with a BSF layer thickness of 30 nm and doping concentration of 1E18 cm⁻³. Next, an optimization of BSF layers thickness has been conducted. The optimum value of thickness is considered at 40 nm with an enhancement ratio in efficiency of 36.70%, 26.21% and 21.53% for SnS, CZTSSe and CZTSe, respectively. Better performances have been noted for SnS material. The optimized CZTSSe solar cell with SnS as a BSF layer achieves an efficiency of 16.95% with J_SC = 36.34 mA/cm², V_OC = 0.69 V, and FF = 67% under Standard Test Conditions (AM1.5 G and cell temperature of 25 °C).     

Semipolar (11\bar 2\bar 2) ZnO thin films grown on LaAlO3‐buffered LSAT (112) single crystals by pulsed laser deposition

Semipolar (11\bar 2 \bar 2) ZnO was successfully grown on (112) LaAlO₃/(LaAlO₃)_0.29(Sr₂AlTaO₆)_0.35 substrate by pulsed laser deposition. The epitaxial relationship is [11\bar 23]_{\rm ZnO} // [11\bar 1]_{\rm LAO/LSAT} with the polar axis of [000\bar 1]_{\rm ZnO} pointing to the surface. For ZnO films with thickness of 1.6 μm, the threading dislocation density is ～1 × 10⁹ cm^–2, and the density of basal stacking faults is below 1 × 10⁴ cm^–1. The (11\bar 2 \bar 2) ZnO exhibits strong D⁰X emissions with a FWHM of 9 meV and very few green–yellow emissions in the low‐temperature (10 K) and room‐temperature photoluminescence spectra, respectively.

     

Ionic liquids based on the bis(trifluoromethylsulfonyl)imide anion for high‐pressure Raman spectroscopy measurements

Assembling a diamond anvil cell for high‐pressure measurements involves placing in a gasket hole the sample of interest, a pressure transmitting fluid, and a material for pressure calibration. In this communication, we propose the use of ionic liquids containing the bis(trifluoromethylsulfonyl)imide anion ([Tf₂N]^‐), [(CF₃SO₂)₂ N]^‐, as a simultaneous pressure transmitting and calibrant material for high‐pressure Raman spectroscopy measurements of solid samples that are not soluble in ionic liquids. The position of the characteristic Raman band of the [Tf₂N]^‐ anion at 740 cm⁻¹ exhibits linear frequency shift for pressures up to 2.5 GPa. High‐pressure Raman spectra of different ionic liquids containing the same anion indicate that the actual magnitude of the pressure‐induced frequency shift of the [Tf₂N]^‐ normal mode depends on the counterion, the typical shift being 4.2 cm⁻¹/GPa. Ionic liquids based on the [Tf₂N]^‐ anion are also good pressure transmitting mediums because hydrostatic condition is kept at high pressure, and no crystallization is observed up to 4.0 GPa. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural, optical and electronic properties of P doped p-type ZnO thin film

P doped ZnO films were grown on quartz by radio frequency-magnetron sputtering method using a ZnO target mixed with 1.5 at% P₂O₅ in the atmosphere of Ar and O₂ mixing gas. The as-grown P doped ZnO film showed n-type conductivity, which was converted to p-type after 800 °C annealing in Ar gas. The P doped ZnO has a resistivity of 20.5 Ω cm (p∼2.0×10¹⁷ cm⁻³) and a Hall mobility of 2.1 cm² V⁻¹ s⁻¹. XRD measurement indicated that both the as-grown and the annealed P doped ZnO films had a preferred (0 0 2) orientation. XPS study agreed with the model that the P_Zn-2V_Zn acceptor complex was responsible for the p-type conductivity as found in the annealed P-doped ZnO. Temperature-dependent photoluminescence (PL) spectrum showed that the dominant band is located at 3.312 eV, which was attributed to the free electronic radiative transition to neutral acceptor level (FA) in ZnO. The P_Zn-2V_Zn acceptor complex level was estimated to be at E_V=122 meV.