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The structure of bridged NWs effectively blocks the Joule heat dissipation/conduction from the (tip) bridged NWs to the (bottom) substrate and offers high utilization efficiency of Joule heat compared with film NWs device, resulting in low power use.

Metastable β-W films play an essential role in the low-temperature (400 °C) thermal oxidation growth of W18O49 nanowire arrays.

Discriminating structurally similar volatile organic compounds (VOCs) molecules, such as benzene, toluene, and three xylene isomers (BTX), remains a significant challenge, especially, for metal oxide semiconductor (MOS) sensors, in which selectivity is a long-standing challenge. Recent progress indicates that temperature modulation of a single MOS sensor offers a powerful route in extracting the features of adsorbed gas analytes than conventional isothermal operation. Herein, a rectangular heating waveform is applied on NiO-, WO3-, and SnO2-based sensors to gradually activate the specific gas/oxide interfacial redox reaction and generate rich (electrical) features of adsorbed BTX molecules. Upon several signal preprocessing steps, the intrinsic feature of BTX molecules can be extracted by the linear discrimination analysis (LDA) or convolutional neural network (CNN) analysis. The combination of three distinct MOS sensors noticeably benefits the recognition accuracy (with a reduced number of training iterations). Finally, a prototype of a smart BTX recognition system (including sensing electronics, sensors, Wi-Fi module, UI, PC, etc.) based on temperature modulation has been explored, which enables a prompt, accurate, and stable identification of xylene isomers in the ambient air background and raises the hope of innovating the future advanced machine olfactory system.

Insufficient limit of detection (LoD) toward volatile organic compounds (VOCs) hinders the promising applications of metal oxide chemiresistors in emerging air quality monitoring and/or breath analysis. There is an inherent limitation of widely adopted strategies of creating sensitive chemiresistors then operating at the optimized temperature via a continuous heating (CH) mode. Herein, a strategy combining Pt single atoms anchoring (chemical sensitization) with pulsed temperature modulation (PTM, physical sensitization) is proposed. Apart from generating abundant surface asymmetric oxygen vacancy (Pt-V

Recent advances in heterogeneous catalysts indicate that single atoms (SAs), anchored/stabilized on metal oxide nanostructures, exhibit not only high catalyst atom efficiency but also intriguing reactivity and selectivity. Herein, isolated Pt SA-anchored CuCrO

In this work, p-type Co \begin{document}$_3$\end{document} O \begin{document}$_4$\end{document} decorated n-type ZnO (Co \begin{document}$_3$\end{document} O \begin{document}$_4$\end{document} /ZnO) nanocomposite was designed with the assistance of bacterial cellulose template. Phase composition, morphology and element distribution were investigated by XRD, SEM, HRTEM, EDS mapping and XPS. Volatile organic compounds (VOCs) sensing measurements indicated a noticeable improvement of response and decrease of working temperature for Co \begin{document}$_3$\end{document} O \begin{document}$_4$\end{document} /ZnO sensor, in comparison with pure ZnO, i.e., the response towards 100 ppm acetone was 63.7 (at a low working temperature of 180 ℃), which was 26 times higher than pure ZnO (response of 2.3 at 240 ℃). Excellent VOCs response characteristics could be ascribed to increased surface oxygen vacancy concentration (revealed by defect characterizations), catalytic activity of Co \begin{document}$_3$\end{document} O \begin{document}$_4$\end{document} and the special p-n heterojunction structure, and bacterial cellulose provides a facile template for designing diverse functional heterojunctions for VOCs detection and other applications.

As one of the bottleneck parameters for practical applications of metal oxide semiconductor-based gas sensors, sensitivity enhancement has attracted significant attention in the past few decades. In this work, alternative to conventional strategies for designing sensitive surfaces via morphology/defect/heterojunction control (then operating at an optimized isothermal temperature with a maximal response), a facile enhancement approach by decoupling surface charge exchange and resistance reading process (possessing different temperature-dependent behaviors) through pulsed temperature modulation (PTM) is reported. Substantially magnifying electrical responses of a generic metal oxide (e.g., WO3) micro-electromechanical systems sensor toward diverse analyte molecules are demonstrated. Under the optimal PTM condition, the response toward 10 ppm NO2 can be boosted from (isothermal) 99.7 to 842.7, and the response toward 100 ppm acetone is increased from (isothermal) 2.7 to 425, which are comparable to or even better than most of the state-of-the-art WO3-based sensors. In comparison to conventional (isothermal) operation, PTM allows to sequentially manipulate the physisorption/chemisorption of analyte molecules, generation of surface reactive oxygen species, and sensor resistance reading and thus provides additional opportunities in boosting the electrical response of oxide sensors for advanced health and/or environment monitoring in future.

Poor selectivity of metal oxide semiconductor (MOS) gas sensors (toward volatile organic compounds, VOCs) poses a significant challenge for their applications in the emerging areas of personal health and air quality monitoring. Extensive efforts have been devoted to improving the selectivity of gas sensors via extracting features from their electrical response signals. Alternative to the conventional strategy of enlarging the number of sensor arrays, analyzing the transient signal of a temperature modulated gas sensor provides an efficient approach to extract molecule features. Despite p-type MOS outperforms n-type counterpart in terms of (photo)catalytic properties, further exploration on thermal modulation of p-type MOS sensor has been scarcely reported. In this work, p-type NiO nanoparticles with grain size of 17.4 ± 4.0 nm have been synthesized with the assistance of bacterial cellulose (BC) scaffold. Transient response characteristics of NiO sensor (modulated by a staircase waveform) toward 5 kinds of VOCs have been investigated. The removals of irrelevant electrical signals, particularly induced by large temperature coefficient of resistance (TCR) of p-NiO, allows us to extract the intrinsic features of tested VOCs molecules by discrete wavelet transform (DWT). Successful classification and recognition of tested VOCs molecules, including three kinds of benzene series (benzene, toluene and chlorobenzene), have been achieved by typically non-selective p-type NiO sensor with a low sensitivity. Our work highlights that eliminating the irrelevant thermally modulated electric signals is essential for expanding the recognition capability of a single MOS sensor (toward VOCs molecules), and sheds light on the exploring future smart gas molecule recognition chips.

Metal oxide semiconductor (MOS) gas sensors operated at room temperature (RT) hold great promise for environmental monitoring in the emerging smart society. An in-depth understanding of the gas/MOS interfacial charge exchange under the ambient moist atmosphere is essential for subsequent molecule recognition. Herein, delafossite p-CuScO2 with a unique oxygen intercalation property was utilized. Eight orders of resistance tuning could be rationally achieved via controlling oxygen intercalation realized by air annealing (without altering the size and morphological properties), which allows extraction of both the intrinsic (gas/MOS interaction, p-type response) and extrinsic (gas/H2O/MOS interaction, pseudo-n-type response) sensing mechanisms upon exposure to ammonia molecules. This work could provide an insight into the underlying sensing mechanism of RT sensors working in an ambient moist atmosphere, and the unique n- to p-type switching contains rich molecule related features that could be potentially explored for molecule recognition.

Exploring novel ammonia sensors operated at room temperature holds great promise for various applications. Herein, we synthesized p-type delafossite AgAlO2 nanoparticles via hydrothermal method. The nanoparticles show a single Ag-deficient 3R delafossite phase with particle size between 200 and 500 nm. The sensor based on AgAlO2 nanoparticles exhibits high sensitivity, fast response-recovery and good selectivity to 100 ppm ammonia at 293 K 20–70 %RH. More interestingly, the sensor shows a pseudo n-type response to ammonia at 293 K 35 %RH, but a p-type sensing behavior at elevated temperature of 573 K. The temperature-dependent pseudo n-type response to ammonia gas is ascribed to the competition of extrinsic and intrinsic sensing behaviors, which resulted from the reaction of ammonia gas with surface adsorbed water molecules and adsorbed oxygen ions, respectively. The former can regulate the conduction of the adsorbed water layer, which contributes to the total conductivity as an external part, while the latter can modulate the intrinsic conductivity of the sensor by changing the hole concentration of AgAlO2. This work might provide a new idea to design low temperature gas sensors.

Ar&H2 plasma treatment was proposed to enhance the response of a p-CuAlO2 sensor toward volatile organic compounds. Comprehensive defect characterization studies indicate a substantial increase of surface unsaturated oxygen vacancy (VO) defects via plasma treatment, which could provide active sites for molecule adsorption and the subsequent interfacial redox reaction.

Exploring novel sensing materials enabling selective discrimination of trace ambient H

Though UV illumination has been widely adopted to activate the room temperature response of metal oxide based chemiresistors, photoexcited abundant carriers (low base resistance) induced low response, and UV induced hydrophilicity caused degradation or even poisoning in ambient humid air atmosphere, pose a challenge for real applications. Herein, 15 mol% (optimized ratio) ZnO nanoparticles have been coupled into hydrophobic (Sr0.6Bi0.305)2Bi2O7 (SBO) matrix, hydrophobic ZnO/SBO chemiresistor has been proposed. Visible 455 nm light could not only trigger the gas/oxide interfacial charge exchange, but also substantially reduce the carrier concentration of chemiresistor in comparison with UV 365 nm light, and therefore noticeably boosts trimethylamine (TMA) response at room temperature, including an enlarged sensitivity, extremely low limit of detection (LoD) (10 ppb), good selectivity, reproducibility and long-term stability. More importantly, present hydrophobic ZnO/SBO chemiresistor could be operated under high relative humidity (RH 90%) with a slight decline (17%) of response with respect to dry air background, opening an opportunity for the practical applications of oxide chemiresistors in ambient humid atmosphere.

p-type ternary oxides can be extensively explored as alternative sensing channels to binary oxides with diverse structural and compositional versatilities. Seeking a novel approach to magnify their sensitivities toward gas molecules, e.g., volatile organic compounds (VOCs), will definitely expand their applications in the frontier area of healthcare and air-quality monitoring. In this work, delafossite CuCrO2 (CCO) nanoparticles with different grain sizes have been utilized as p-type ternary oxide sensors. It was found that singly ionized oxygen vacancies (Vo•) defects, compared with the grain size of CCO nanoparticles, play an important role in enhancing the charge exchange at the VOCs molecules/CCO interface. In addition to suppressing the hole concentration of the sensor channel, the unpaired electron trapped in Vo• provides an active site for chemisorptions of environmental oxygen and VOCs molecules. The synergetic effect is responsible for the observed increase of sensitivity. Furthermore, the sensit...

Owing to the unique merits of high sensitivity and large range detection, long-period grating (LPG) optical fiber sensor modified with functional coatings has attracted significant attention recently. As a refractive index sensor, the appropriate choice of the coating properties is critical for exploring the high-performance LPG sensor. In this study, p-type delafossite AgAlO2 (AAO) nanoparticles were proposed as a novel sensitive coating material for the cladding modification of LPG develop a high-sensitivity fiber-optic ammonia sensor. As the resistance/dielectric constant of AAO cladding layer is sensitive to concentration variation of ammonia vapor even at room temperature. Sensing performances of the LPG optical fiber sensor could be substantially enhanced with the presence of AAO cladding layer. A linear sensitivity of 2.07 pm/ppm to ammonia from 25 ppm to 400 ppm was achieved at room temperature. Moreover, the LPG sensor exhibits short response (38 s) and recovery time (50 s), and high selectivity to ammonia compared to several possible interfering vapors.

Exploring novel sensing materials enabling selective discrimination of trace ambient H2S at lower temperature is of utmost importance for diverse practical applications. Herein, heterostructural (Sr0.6Bi0.305)2Bi2O7/ZnO (SBO/ZnO) nanomaterials were proposed. Synergetic effect of promoting analyte adsorption (via multiplying oxygen vacancy defects) and reversible sulfuration-desulfuration reaction induced unique band alignment among SBO/ZnO/ZnS, contributes to the sensitive and selective response toward H2S molecules. Novel SBO/ZnO (10%) sensor possesses excellent sensing H2S performances, including a high response (107.6 for 10 ppm), low limit of detection of 20 ppb, good selectivity and long-term stability. Together with the merits of low operation temperature of 75 °C and weak humidity dependence (endowed by the hydrophobic SBO), present heterostructural SBO/ZnO sensor paves the way for the practical monitoring of trace H2S pollutants in diverse workplaces including petroleum and natural gas industries.

ArH2 plasma treatment was proposed to enhance the response of a p-CuAlO2 sensor toward volatile organic compounds. Comprehensive defect characterization studies indicate a substantial increase of surface unsaturated oxygen vacancy (VO) defects via plasma treatment, which could provide active sites for molecule adsorption and the subsequent interfacial redox reaction.

Metal oxide semiconductor (MOS) gas sensors operated at room temperature (RT) hold great promise for environmental monitoring in the emerging smart society. An in-depth understanding of the gas/MOS interfacial charge exchange under the ambient moist atmosphere is essential for subsequent molecule recognition. Herein, delafossite p-CuScO

Seeking a facile approach to directly assemble bridged metal oxide nanowires on substrates with predefined electrodes without the need for complex postsynthesis alignment and/or device procedures will bridge the gap between fundamental research and practical applications for diverse biochemical sensing, electronic, optoelectronic, and energy storage devices. Herein, regularly bridged CuO microhemisphere nanowire arrays (RB-MNAs) are rationally designed on indium tin oxide electrodes via thermal oxidation of ordered Cu microhemisphere arrays obtained by solid-state dewetting of patterned Ag/Cu/Ag films. Both the position and spacing of CuO microhemisphere nanowires can be well controlled by as-used shadow mask and the thickness of Cu film, which allows homogeneous manipulation of the bridging of adjacent nanowires grown from neighboring CuO hemispheres, and thus benefits highly sensitive trimethylamine (TMA) sensors and broad band (UV-visible to infrared) photodetectors. The electrical response of 3.62 toward 100 ppm TMA is comparable to that of state-of-the-art CuO-based sensors. Together with the feasibility of in situ assembly of RB-MNAs device arrays via common lithographic technologies, this work promises commercial device applications of CuO nanowires.

Alkali metal bis(trifluoromethanesulfonyl)imide (TFSI) modification of TiO2 electron transport layer (ETL) has been widely adopted to improve the performance of perovskite solar cells (PSCs), however, only a handful of investigations have proposed some corresponding mechanisms, and more in-depth investigations are urgent. In this investigation, Li-TFSI and K-TFSI were adopted to modify mesoporous TiO2 (me-TiO2) ETL of PSCs, electrochemical impedance spectroscopy, photoluminescence spectrum, space-charge limited current, and X-ray photoelectron spectroscopy measurements were performed to investigate the modification mechanisms. Alkali metal-TFSI modification could passivate the oxygen vacancies in me-TiO2 ETL and suppress the charge recombination effectively, improve the contact between me-TiO2 ETL and perovskite layer and increase the conductivity of me-TiO2 ETL which lead to rapid charge extraction and transfer at ETL/perovskite interface and balance the electron flux and hole flux in devices. Moreover, sulfates induced by alkali metal-TFSI act as nucleation sites in the crystallization process of perovskite which could increase the grain size and improve the uniformity of CH3NH3PbI3 films obviously, and it is a positive factor for suppressing charge recombination and improving the cell performance. As a result, the power conversion efficiencies of the champion devices for Li-TFSI and K-TFSI modified PSCs have reached 20.02% and 19.64%, respectively.

Though p-type NiO possesses excellent catalytic oxidation property toward volatile organic compounds (VOCs), intrinsic low sensitivity of NiO (arising from the hole accumulation layer configuration in ambient air atmosphere sensor) restricts its promising applications in VOCs detection. In this study, Sc and Li were proposed to modulate the (surface) properties of NiO nanosheet-flowers based sensors. At the optimal 2 at.% Sc and 5 at.% Li doping ratio (Ni0.93Sc0.02Li0.05O), the sensitivity to 100 ppm ethanol is 118.4 (105 times higher than that of pure NiO), which is comparable to or even higher than most of reported NiO based sensors. Moreover, Ni0.93Sc0.02Li0.05O sensor exhibits a low detection limit of 10 ppb, excellent repeatability and long-term stability (∼30 % decline of response after 7 months). Apart from regulating the carrier concentration, defect characterizations indicate a noticeable increase of stabilized surface oxygen vacancy (OV) defects and Ni3+ cations by Sc3+ and Li+ co-doping, which greatly facilitate the adsorption of VOCs molecule (revealed by density functional theory calculation) as well as the subsequent VOCs/NiO interfacial charge interaction, thus contribute to the superior sensing performances. This work demonstrates that co-doping offers an effective avenue for boosting the performances of (p-type) oxide sensors.

Identifying the defect type which closely correlates with gas/metal oxide semiconductor (MOS) interfacial charge exchange is of utmost importance for rationally designing high performance MOS gas sensors, which are essential for the emerging sensing electronics for assessing the personal health and environment pollution. Herein, we report the sensing performance of p-type NiO toward volatile organic compounds (VOCs) molecules could be drastically improved by Sc dopant. At an optimal doping ratio of 7.4 at.%, the sensor response to 100 ppm acetone was boosted from 8.2 (pure NiO) to 109.4, with a low detection limit of 10 ppb. Comprehensive defect characterizations indicate surface unsaturated oxygen vacancy (VO) defects act as active sites that facilitate the interfacial charge exchange at elevated temperatures. Our work highlights that abundant VO defects induced by aliovalent Sc dopant play an important role in boosting the sensitivity of p-type NiO toward VOCs, and provide valuable guidance in designing high performance p-type MOS sensors.

Pure phase CuFeO 2 powders with specific surface area of 6.5 m 2 g −1 were synthesized by a self-combustion glycine nitrate process. The powders show a coral-like network structure with a wall thickness of about 100 nm and pore sizes ranging from tens of nanometers to hundreds of nanometers in diameter. The CuFeO 2 powders were first applied as photocathodes for p-type dye-sensitized solar cells with coumarin 343 as sensitizer and iodide/triiodide (I − /I 3 − ) as redox mediator. The sintering process and thickness of the CuFeO 2 photocathode films were roughly optimized. The optimized CuFeO 2 based solar cell has achieved the best open circuit voltage of 365 mV under 1 Sun AM 1.5 illumination. This record is significantly high in comparison to p-DSSCs based on NiO or other delafossites tested in the similar LiI/I 2 electrolyte solutions. This is mainly due to the much deeper valence band (0.69 V vs . NHE) of CuFeO 2 than that of the commonly used NiO (0.54 V vs . NHE).

Transparent conducting amorphous p-type CuFeO2 (CFO) thin film was prepared by radio-frequency (RF) magnetron sputtering method at room temperature using polycrystalline CuFeO2 target. Amorphous structure of as-deposited film was confirmed by XRD. XPS analysis convinced that the chemical state of Cu+ and Fe3+ in the film, and the chemical composition of the thin films is close to the stoichiometry of CuFeO2. Surface morphology of the film was analysed by SEM studies. p-type nature and concentration of carriers was investigated by Hall effect measurement. The p–n heterojunction in the structure of Al/n-Si/p-CuFeO2/Al showed good rectifying behaviour with a forward and reverse currents ratio of 555 at 2 V. The turn-on voltage and reverse leakage current values were found to be 0.9 V and 4 μA at −2 V. Further, the conduction mechanism of forward bias voltage was controlled by thermionic emission (TE) and trap-space charge limited current (TCLC) mechanisms.

The role of remnant PbI2 in CH3NH3PbI3 films is still controversial, some investigations have revealed that the remnant PbI2 plays a passivation role, reduces the charge recombination in perovskite solar cells (PSCs), and improves the performance of PSCs, but the opposing views state that remnant PbI2 has no passivation effect and it would deteriorate the stability of the devices. In our investigation, the CH3NH3PbI3 films have been prepared by a two-step spin-coating method and the content of the remnant PbI2 in CH3NH3PbI3 films has been tuned by varying the preparation temperature. It has been found that increasing the heating temperature could increase the coverage of spin-coated PbI2 films, which has led to high coverage CH3NH3PbI3 films and more remnant PbI2 in CH3NH3PbI3 films, and as a result, the performance of PSCs was enhanced obviously and the maximum power conversion efficiency of 14.32 ± 0.28% was achieved by the PSCs prepared at 130/120 °C (PbI2 films were heated at 130 °C and CH3NH3PbI3 films were heated at 120 °C). Furthermore, the dark current, electrochemical impedance spectroscopy and time-resolved fluorescence emission decay measurements revealed that the charge recombination in PSCs has been gradually suppressed and the fluorescence emission lifetime has gradually increased with the content of remnant PbI2 increasing. Thus, the passivation effects of the unreacted and decomposed PbI2 in improving the performance of PSCs have been confirmed unquestionably.

Exploring novel sensing materials with extraordinary specificity/selectivity is essential to construct artificial gas molecules recognition chips (sensor arrays) for future environment and health monitoring. Herein, we reported the excellent H2S sensing properties of a p-type delafossite CuAlO2 sensor. Without complex size, morphology or defect control procedures, irregularly shaped CuAlO2 particles (size ranging from tens of nm to several μm) synthesized by a simple sol-gel route, exhibit an ultrahigh response (4600) toward (10 ppm) H2S molecules at 160 °C. Tiny responses (

The laser-induced damage threshold of a calcium fluoride (CaF2) single crystal was obtained by a 193 nm ArF excimer laser. The damage morphology of the crystal was analyzed. The results showed that the surface of CaF2 single crystal broke along the natural cleavage plane under ArF excimer laser irradiation, some fragments fell off, and Newton’s rings were observed on the curved fragments. Laser-induced periodic stripe structures (LIPSS) appeared on the surface layer beneath the fragments that peeled off. The spacing of LIPSS was measured, and the formation mechanism of LIPSS was analyzed based on the interference model.

p-type ternary oxides can be extensively explored as alternative sensing channels to binary oxides with diverse structural and compositional versatilities. Seeking a novel approach to magnify their sensitivities toward gas molecules, e.g., volatile organic compounds (VOCs), will definitely expand their applications in the frontier area of healthcare and air-quality monitoring. In this work, delafossite CuCrO

CuCr 0.97 Mg 0.03 O 2 thin films were prepared by direct current magnetron sputtering under various percentage of oxygen flow rate (P O ) followed by post-annealed in N 2 atmosphere. The microstructures, optical and electrical properties of the films were investigated. The film deposited in pure Ar atmosphere showed pure CuCrO 2 phase, while the films deposited in O 2 and Ar mixture atmosphere showed CuO and CuCr 2 O 4 mixture phase. After post-annealed at 800 °C, the films deposited in O 2 and Ar mixture atmosphere turned into c-axis oriented single-phase CuCrO 2 which showed much better transparency and electrical conductivity than the film deposited in pure Ar. The film deposited in P O = 40% with thickness of 350 nm showed the lowest resistivity of 0.4 Ω cm and transmittance over 60% in visible light region.

Amorphous CuFeO 2 thin films were prepared on Al 2 O 3 (001) substrates by radio-frequency magnetron sputtering method at room temperature. Various oxygen partial pressures P O in the sputtering gas ambient (9.1%, 11.1% and 13.0%) were used in the deposition experiments. X-ray photoelectron spectroscopy analysis convinced the chemical state of Cu + and Fe 3 + in the films, and the chemical compositions of the thin films are close to the stoichiometry of CuFeO 2 . The content of oxygen composition increased systematically with increasing P O . From the optical transmission spectra, only one absorption edge could be observed during 200–1200 nm for all the films with a band gap around 3.25 eV. This result is different from the polycrystalline CuFeO 2 films which have 3 absorption edges in the range of 200–1200 nm. This interesting result indicates that amorphous CuFeO 2 thin films have much different electronic energy band with polycrystalline ones. The resistivity of the films first decreases and then increases with increasing P O . The minimum resistivity of 4.2 Ω cm with optical transmittance of 47% at 600 nm is obtained for the film deposited in P O = 11.1%.

Single phase CuFeO 2 thin films with c-axis orientation were prepared by RF sputtering method at room temperature under oxygen partial pressure P O from 5% to 15% and then post annealed at 900 °C for 4 h in flowing N 2 atmosphere. The grains of the films show layer-by-layer structure and are closely gathered and densely arranged. The E g at near-UV region shows a redshift with increment of P O which may due to the impurity levels induced by oxygen interstitials. The resistivity of the films first decreased and then increased with increasing P O . The minimum resistivity of 0.32 Ωcm at room temperature for the sample 10%-PA is nearly two-order magnitude smaller than that (18 Ωcm) for 5%-PA. Oxygen interstitial doping can effectively enhance the conductivity of CuFeO 2 thin films.

Vacuum thermal evaporated Cu x S (VTE-Cu x S) film on fluorine-doped tin oxide substrate has been investigated as counter electrode (CE) for quantum dot-sensitized solar cells (QDSCs) with polysulfide electrolyte. The photovoltaic parameters of QDSCs show an obvious dependence on the annealing time of Cu x S film, and the maximum power conversion efficiency of 3.16 ± 0.05% under one sun illumination (100 mW cm −2 , AM 1.5 G) was obtained when the VTE-Cu x S CE was annealed at 270 °C for 300 s (VTE-Cu x S-300s CE). Electrochemical impedance spectroscopy, Tafel polarization, and cyclic voltammetry measurements have been employed to investigate the electrocatalytic activity of VTE-Cu x S-300s CE. The electrocatalytic activity of the VTE-Cu x S-300s CE is much higher than that of Pt CE, and is slightly higher than that of Cu 2 S CE in situ prepared on brass sheet. In particular, VTE-Cu x S-300s CE holds high diffusion velocity of S 2− /S n 2− in polysulfide electrolyte, and the stability of its electrocatalytic activity in polysulfide electrolyte is better than that of Pt and Brass-Cu 2 S CEs obviously.

The anatase TiO 2 nanoparticle films with different thicknesses have been fabricated through screen printing method, and CdS and CdSe quantum dots (QDs) have been deposited on TiO 2 films in turn through successive ionic layer adsorption and reaction (SILAR) method. It has been found that the amount of QDs decreases significantly and the size of QDs increases obviously with the depth increasing in TiO 2 nanoparticle films, and the size distribution of QDs shifts to large-size direction with the TiO 2 film thickness increasing. Furthermore, a qualitative model of CdS/CdSe quantum dot distribution in TiO 2 nanoparticle films has been obtained. After optimizing the TiO 2 film thickness, the quantum dot-sensitized solar cells (QDSCs) with about 10 μm thick nanocrystalline TiO 2 electrodes and Pt counter electrodes have reached relatively high power conversion efficiencies of 3.26 ± 0.10% under one sun illumination (100 mW cm −2 , AM 1.5 G).

Single phase delafossite CuFeO2 thin films were synthesized by a simple sol–gel method. The influence of polyethylene glycol (PEG) on the morphology and optoelectronic properties of the films was studied by addition of 1.0 g PEG in 10 ml precursor solution. The crystal sizes of the derived CuFeO2 films with and without addition of PEG were 49 nm, but the sample with addition of PEG (labeled as CFO-PEG) showed weaker c-axis orientation growth. The sample without addition of PEG (labeled as CFO) showed a compact surface without detectable pores and had a thickness around 50 nm. However, the sample CFO-PEG exhibited a porous surface with worm-like grains in nanometric scale and had a thickness around 310 nm. Enhanced absorbance in UV–vis region was observed for the sample CFO-PEG which might ascribe to both the thickness and porous surface. The optical direct bandgaps at near-UV were estimated to be ~3.0 and 3.38 eV for the sample CFO-PEG and CFO, respectively. Though the porous surface of CFO-PEG has improved the absorbance in UV–vis region, the resistivity has also been increased due to the homogeneous distribution of interspaces between the worm-like grains, which makes the incident photon to current efficiency of CFO-PEG lower than that of CFO.

CuFe1−xMgxO2 (0 ⩽ x ⩽ 0.05) thin films were synthesized by a simple sol–gel method. The structural and optoelectronic properties of the films were studied. Single phase CuFeO2 thin films with c-axis orientation were obtained on sapphire substrates and secondary phase was not detected by XRD measurements in the studied doping range. The resistivity of the films first decreased and then increased with increasing x. The minimum resistivity was observed as 3.23 Ω cm at room temperature for the doping amount of x = 0.02. The transmittance of all the films was around 37% in the wavelength of 600 nm and three absorb edges were observed in the wavelength range of 200–1100 nm. The optical direct bandgaps of CuFeO2 were estimated to be ∼3.38 eV, 2.04 eV and 1 eV, respectively.

TiCl 4 solution growth has been introduced to modify the single-crystal rutile TiO 2 nanorod arrays (TNRs) used as photoanodes of dye-sensitized solar cells (DSSCs). After modification, a large number of rutile TiO 2 nanoparticles have been synthesized on the surface of TNRs. The surface area and dye adsorption of these modified TNRs increase obviously, and their photovoltaic performance improves significantly. The maximum energy conversion efficiency of 4.14 ± 0.07% has been obtained when the concentration of TiCl 4 solution is 0.2 M and the growth time is 36 h. To obtain similar energy conversion efficiencies the single-crystal TNRs based DSSCs need far less amount of dye than P25 TiO 2 nanoparticles based DSSCs. Contrary to previous publications, the electron transport rate of bare and modified single-crystal rutile TNRs with one-dimensional nanostructures is slower than that of P25 TiO 2 nanoparticles film. But the increase of the electron recombination lifetime of the bare and modified single-crystal rutile TNRs compensates for the slower electron transport rate, and makes them have similar charge-collection efficiencies to that of P25 TiO 2 nanoparticles based DSSCs.

Based on the preparation of flexible dye-sensitized solar cells (DSC) by cold isostatic pressing method, optimization of the paste and tandem DSC were investigated. The results presented that hydrothermal treatment of P25 paste could improve the stability of the paste and the efficiency of DSC obviously. Proper amount of 200 nm TiO2 particles was added to the P25 paste to enhance light scattering of photoelectrode. The highest conversion efficiency of 3.11% was obtained at the 4:1 ratio of P25 to 200 nm TiO2. Subsequently, N719 and N749 double-layer tandem DSC were studied. The results show that the efficiency of the double-layer tandem DSC is higher than that of N749 totally sensitized DSC but lower than that of N719 totally sensitized DSC. This may be caused by that thicker photoelectrode hampers the electronic transmission and dyes contact impacts the purity of dyes. The thickness of photoelectrode and cell structure need to be optimized.