Heterojunction Films Research Articles

Solar-driven WO3·H2O/TiO2 heterojunction films immobilized onto bamboo biotemplate: Relationship between physical color, crystal structure, crystal morphology, and energy storage ability

In this study, different morphologies of WO3⋅H2O/TiO2 (WT) heterojunction films were successfully synthesized on bamboo biotemplate via facile two-step hydrothermal deposition methods. The WO3·H2O self-assembled by nanosheets or nanoplates on anatase TiO2-coated bamboo (TiO2-B) exhibited a distinctive surface color. The addition of WO3·H2O could significantly extend the optical responses of TiO2-B in the ultraviolet to the visible region. Based on the various analysis techniques, the formation mechanisms of the WO3·H2O hierarchical architectures with different crystal structures were also proposed. In addition, the photoactivity and post illumination activity of WT films were examined by constructing ·O2ˉ and ·OH in light and in light-off, respectively. The results showed that WT films with different crystal structures exhibited different photoactivity and energy storage abilities, and the photoactivity of WT films was negatively correlated with their energy storage ability. The presence of an anatase TiO2 thin film on the bamboo surface provided abundant active sites for WO3·H2O growth, which formed direct S-scheme heterojunctions for solar energy conversion and storage. Therefore, we anticipate that solar-driven energy storage heterojunctions with accessible and rich crystal morphologies will provide new insights for various applications, such as efficient wastewater treatment, self-cleaning coating, and air purification.

High responsivity n-ZnO/p-CuO heterojunction thin film synthesised by low-cost SILAR method for photodiode applications

In this report, we have prepared n-ZnO/p-CuO heterojunction thin film by low-cost SILAR method and made a comparative study with physical properties of ZnO and CuO thin film photodetectors. The prepared heterojunction film is exhibit mixture of hexagonal structure of ZnO and monoclinic structure of CuO. All the films have uniform surface morphology without any voids and ensured that the presence of used elements like Zn, Cu, and O. The optical absorption spectrum declared that comparatively high photon absorption in the range of 2–6% occurred in 365 nm of UV light. The photoluminescence spectrum notices that different kind of point defects are present in the prepared heterojunction film. The photo sensing results announce that the ZnO/CuO heterojunction film exist a good photodiode characteristic behavior with good responsivity of 43.69 × 10−2 A/W.

Photostability of benzodithiophene based polymer: effect of PC60BM and intermolecular interactions

Organic solar cells working under continuous light irradiation are prone to photo-induced degradation. Photostabilities of benzodithiophene-alt-2-decyltetradecyl substituted isoindigo (PBDTI-DT) copolymer in solution, and as pristine film, and a PBDTI-DT:PC60BM bulk hetero-junction (BHJ) film were investigated for more than 70 h under simulated AM 1.5 solar irradiation. The photodegradation kinetics studied in standalone polymer chains were found to be fast due to the absence of intermolecular interaction while the inter-chain interaction in the polymer films kept the backbone intact against light-induced degradation. Further addition of PC60BM in the polymer made the BHJ film more stable as PC60BM serves as photoprotective layer and radical scavenger. This conclusion was supported by the similar XRD traces of PBDTI-DT:PC60BM film during degradation while the traces of the pristine film indicated bleaching and shifted with increasing photon stress. In addition, the absorption of PBDTI-DT:PC60BM and pristine PBDTI-DT films were reduced to 80 and 56%, respectively, after 70 h of photo-degradation.

Excitonic effects in the linear and nonlinear optical properties of ZnO@WS2 heterojunction films under photoexcitation

The excitation effects of linear and nonlinear optical properties for the ZnO@WS2 heterojunction (ZWH) films under photoexcitation were studied. We found that intrinsic absorption and radiation of ZWH films from bandgap and defects of ZnO and WS2. "M" and "W" type of Z-scan curve represent mechanism of TPA/3PA induced the ground state/excited state SA or RSA. The transient absorption spectra corresponding to free carriers, trapped carriers, and state filling were observed in the picosecond time region for samples. Our results revealed the carrier relaxation and recombination processes in WS2 and ZWH films, identifying the critical role of stoichiometry in photo-induced phenomena.

A promising patterned mesoscopic CuInS2 solar cell

Bulk heterojunction (BHJ) film is potential for the solar cells based on the photon-absorbers with a limited charge diffusion length. Here, for the first time, a patterned mesoporous film featuring the voids surrounded by the mesoporous walls of TiO2 nanoparticles is created for loading CuInS2 nanoparticles to prepare CuInS2-based BHJ film, resulting in a patterned mesoscopic CuInS2 solar cell with an efficiency of 6.23%. The voids are derived from the phase-separated poly (ethylene glycol) (PEG) aggregates during spin-casting the mixture of TiO2 slurry and PEG. It is demonstrated that the patterned mesoscopic CuInS2 solar cell is much more efficient than conventional/non-patterned counterpart device.

Reproducibility in Time and Space—The Molecular Weight Effects of Polymeric Materials in Organic Photovoltaic Devices

The reproducibility issue is one of the major challenges for the commercialization of large-area organic electronic devices. It involves both the device-to-device variation and opto-electronic properties in different positions of a single thin film. Herein, the molecular weight effects in polymeric semiconductors with three widely used photovoltaic donor materials P3HT, PBDB-T, and PM6 are systematically investigated. A simple but effective method is proposed to evaluate the uniformity of large-area devices by adopting the micron-level grid electrodes in organic thin films. An interesting phenomenon is observed that the device is gradually improved uniformly with the Mw range lower than 100kg mol-1 . In neat films, both the mobility and energetic disorder values of hole carriers exhibit relatively lower coefficient of variation (cv ) in high molecular-weight systems. After blending with the electron-accepting materials, their bulk heterojunction films also enjoy more uniform hole transfer rates, fluorescence lifetimes, and power conversion efficiencies in single and different devices. This work not only proposes a facile approach to evaluate the electrical properties of large-area organic thin films, but also demonstrates the relationship between molecular weight and device reproducibility in polymer solar cells. This contribution provides a new insight into the commercial large-scale production of organic electronics.

Performance investigation of Sb2S3 and Sb2Se3 earth abundant based thin film solar cells

Recently, antimony sulfide (Sb2S3) and antimony selenide (Sb2Se3) materials have received a particular research attention as absorbers in hetero-junction thin film solar cells due to their high optical absorption, low cost, earth abundance, and non-toxic properties. In this work, we investigate numerically Sb2S3 and Sb2Se3 based solar cells and analyze their performance using SILVACO software. A simulation of absorber and buffer layers thickness, radiative recombination coefficient, doping densities in absorbent and buffer regions, defect in absorbent region and at buffer/absorber interface alongside with rear contact metal work function is effectuated in order to optimize these parameters. Absorber's optimal parameters are found to be 1 μm thickness, 10−9 cm3/s radiative recombination coefficient, 5 × 1016 cm−3 acceptor doping density, 1015 cm−3 defect density and 5 eV work function for Sb2S3 and 1.5 μm, 10−9 cm3/s, 1017 cm−3, 1015 cm−3 and 4.5 eV for Sb2Se3. Buffer layer optimal parameters are 20 nm thickness and 1020 cm−3 doping density for Sb2S3 based solar cell and 10 nm and 2 × 1020 cm−3 for Sb2Se3 one. Buffer/absorber interface optimal defect density is 1013 cm−3. PV structures with such optimal parameters give conversion efficiencies of 14.45 and 12.84% for Sb2S3 and Sb2Se3 based solar cells, respectively.

Co-doped amorphous MoSx supported on CuO/CM (Cu mesh) with enhanced photocatalytic activity for ammonia synthesis

As one of the world's most significant industrial synthetic chemicals, ammonia has critical applications in many fields. Mo-based catalyst has an excellent effect on photocatalytic nitrogen fixation. Compared with crystalline molybdenum sulfide, low crystalline or amorphous molybdenum sulfide has rich unsaturated defects to improve the photocatalytic activity. Therefore, we used CuO/CM (Cu mesh) as the substrate and a simple electrochemical deposition method to load amorphous MoSx doped with different contents of Co on CuO/CM and successfully synthesized a thin film heterojunction photocatalyst. At the same time, we fabricated a gas-liquid-solid three-phase photocatalytic reactor to evaluate the catalytic activity of the catalyst. Compared with the powder catalyst reported in the literature, because the catalytic reaction of the three-phase gas-liquid-solid three-phase reactor occurs at the gas-liquid interface, the film catalyst can also absorb sufficient N2 in the gas phase while contacting the liquid proton source (water). It can effectively enhance photocatalytic nitrogen fixation efficiency. The constructed film photocatalyst showed good photocatalytic performance and stable structure under the 350 W simulated light source. While exploring the catalyst structure, the photocatalytic effect of the catalyst was evaluated. When the molar ratio of Mo and Co is 1:0.9, the photocatalyst efficiency shows the high photocatalysis at a rate of 1.062 mg·L−1 for 4 h. Compared with pure CuO / CM and MoSx / CuO / CM, the NH3 yield of the catalyst was increased by 7.86 and 7.52 times, respectively. In addition to N2, no other N sources were introduced during the reaction, which ensured the accuracy of the experimental results.

Hydrothermal fabrication of p‐Cu2O−n‐ZnO films and their properties for photodegradation and ultraviolet sensors

AbstractThis article reports spin coating and hydrothermal approaches to the synthesis of Cu2O seed layer−ZnO and Cu2O film−ZnO heterojunction films on fluorine‐doped tin oxide substrates. Cu2O seed layers and an ethylene glycol (EG) reducing agent were employed to obtain pure, uniform, and adhesive Cu2O films on the substrate. Transmission electron microscopy validated the heterojunctions with clear interfaces between each component on the p‐Cu2O film−n‐ZnO (with EG) sample, the conductive types of which were determined through Mott−Schottky measurements. Constructed energy band diagrams supported the Mott−Schottky result, manifesting favorable conduction band positions for the generation of •O2− radicals for all constituent materials and indicating smooth charge carrier transport for the p‐Cu2O film−n‐ZnO (with EG) sample. Furthermore, abundant p−n junction interfaces synergistically enabled the sample to exhibit the most satisfactory photodegradation capability (rate constant ≈ 8.9 × 10−3 min−1), which was attributable to the predominance of •OH radicals. The sample's rectifying (diode) behavior with a ratio of the current density (J) at +3 V (forward bias) to that at −3 V (reverse bias) of approximately 27 was observed without ultraviolet illumination. Moreover, the J at −3 V is under illumination approximately 80 times that without illumination, implying the suitability of the sample for UV detectability.

High Efficiency Perovskite Solar Cells Employing Quasi‐2D Ruddlesden‐Popper/Dion‐Jacobson Heterojunctions

AbstractWhile 2D Ruddlesden‐Popper (RP) perovskites exhibit attractive opto‐electronic properties and stability for use in perovskite solar cells (PSCs), their complicated film‐forming processes often induce a non‐negligible level of defects that significantly undermine the power conversion efficiency (PCE) and stability of PSCs. Here, the use of two organic ammonium salts with the same chain length, namely monoammonium (butylammonium iodide, BAI) and diammonium (1,4‐butanediamine dihydroiodide, BDAI2) for surface defect passivation of RP‐2D perovskite films of (AA)2MA4Pb5I16 (n = 5) are reported. It is found that the diammonium BDAI2 not only effectively reduces the defect density (similarly to using monoammonium BAI) but forms a Dion‐Jacobson (DJ) 2D structure to enhance interfacial charge extraction and suppress surface charge recombination. As a result, a boosted PCE of 18.34% has been obtained with a high open‐circuit voltage of 1.24 V. Owing to the enhanced structural integrity of the DJ phase, the RP‐2D/DJ‐2D perovskite heterojunction films exhibit supreme material robustness, which translates to the impressive environmental stability of devices, showing nearly zero‐degradation of the efficiency after 800 h of continuous thermal aging (60 °C) for 800 h. This work enriches the fundamental understanding of the impacts of the DJ‐2D structure on the surface properties of 2D perovskites.

Molecular Doping Increases the Semitransparent Photovoltaic Performance of Dilute Bulk Heterojunction Film with Discontinuous Polymer Donor Networks.

The semitransparent and colorful properties of organic solar cells (OSCs) attract intensive academic interests due to their potential application in building integrated photovoltaics, wearable electronics, and so forth. The most straightforward and effective method to tune these optical properties is varying the componential ratio in the blend film. However, the increase in device transmittance inevitably sacrifices the photovoltaic performance because of severe carrier recombination that originates from discontinuous charge-transport networks in the blend film. Herein, a strategy is proposed via the molecular-doping strategy to overcome these shortcomings. It is discovered that p-doping is able to release the trapped holes in segregated polymer domains leading to short-circuit current enhancement, while n-doping is more effective to fill the bandgap states producing a higher fill factor. More importantly, either type of doping improves the photovoltaic performance in the semitransparent photovoltaic devices. These discoveries provide a new pathway to breaking the compromise between the photovoltaic performance and optical transmittance in semitransparent OSCs, and hold promise for their future commercialization.

High fill factor organic solar cells with increased dielectric constant and molecular packing density

<h2>Summary</h2> The fill factor (FF) of organic solar cells (OSCs), a critically important photovoltaic parameter, is still sub-optimal, often less than 0.8. To further reduce the FF gaps with regard to the Shockley-Queisser upper limit, we present a study unveiling the impacts of dielectric properties on obtaining high FFs and photovoltaic efficiencies in OSCs. By increasing the dielectric constant (ε) of non-fullerene acceptors (NFAs) and bulk heterojunction (BHJ) films, afforded by the increase in molecular packing density (MPD) of NFAs in solid states, we show that the FF penalties related to non-geminate charge recombination in OSCs can be appreciably mitigated. In particular, as exemplified by an NFA model system L8-BO tailored with branched side chains, the enlargements of MPD and ε allow achieving an impressive FF of 0.815 with an efficiency of 18.23% in OSCs, featuring an impressively low bimolecular recombination and reduced sensitivity of FF on the BHJ film thickness.

Three-dimensional pyramidal CsPbBr3/C8BTBT film heterojunction photodetectors with high responsivity and long-term stability

A low pressure chemical vapor deposition (CVD) was developed to fabricate CsPbBr3 perovskite film with three-dimensional (3D) pyramidal surface for constructing high-performance and stable photodetectors. The pyramidal CsPbBr3 film is beneficial to increase the absorption and reduce the reflection of light, leading to the improvement of photodetector performance. Moreover, the responsivity and stability could be further improved by constructing a hybrid inorganic/organic film photodetector due to the modification of organic semiconductor C8BTBT on the surface holes and grain boundary junction of CsPbBr3 film. The responsivity of CsPbBr3/C8BTBT photodetector has increased 9.55 times, from 0.42 A/W to 4.01 A/W at 405 nm. The photocurrent of CsPbBr3/C8BTBT photodetector could maintain over 94% of the initial current as exposed to 35% humidity for six months. More importantly, the photocurrent in the current-time (I-T) diagram is stable without attenuation even after the on/off states of the photodetector lasts for 3000 s. The excellent stability under ambient condition resulted from the stable CsPbBr3 film fabricated via CVD and the C8BTBT filled at the perovskite grain boundary. The results have guided significance for the preparation of high-performance and stable perovskite optoelectronic devices.

Bi2S3 nanoparticles/ZnO nanowire heterojunction films for improved photoelectrochemical cathodic protection for 304 SS under visible light

Bi2S3 nanoparticles/ZnO nanowire heterojunction films for improved photoelectrochemical cathodic protection for 304 SS under visible light

Interfacial Charge Transfers and Carrier Regulation Characteristics of Narrow/Wide Band Gap Tmds@Ga2o3 N-N Heterojunction Film

Interfacial Charge Transfers and Carrier Regulation Characteristics of Narrow/Wide Band Gap Tmds@Ga2o3 N-N Heterojunction Film

Performance Assessment of Hetero-Junction Intrinsic Thin Film HIT Photovoltaic Module Using Machine Learning Methods

A solar cell built of ultra-thin amorphous silicon and high-quality mono-crystalline silicon is known as a hetero-junction intrinsic thin film. It has a pyramid surface on the front that increases sunlight absorption. The operating environment has a significant impact on the performance of hetero-junction intrinsic thin-film photovoltaic modules with real I–V (current-voltage) characteristics. Changes in the environment have a significant impact on solar irradiation. Clouds also have a significant impact on the solar irradiation that a PV cell receives. In this project, we will use the Random Forest Regression machine learning algorithm to investigate the effects of sudden changes in environmental conditions on power output and module temperature of an HIT (Heterojunction with Intrinsic Thin Layer) module, where irradiance, temperature, and module efficiency parameters are taken into account when designing modules. The algorithm’s output will be studied to gain a better understanding of performance variations as well as the behavior of the power output and module temperature when subjected to random influences induced by various environmental variables. The suggested algorithm is not restricted to a certain module technology or geographic location.

P-n hybrid bulk heterojunction enables enhanced photothermoelectric performance with UV-Vis-NIR light.

Infrared light accounts for the vast majority of natural light energy, however, the challenge of converting infrared light directly into electricity is too difficult. The photothermoelectric (PTE) effect (connecting the photothermal (PT) and thermoelectric (TE) effects) provides a feasible solution for the indirect conversion of infrared light into electrical energy. Therefore, it is of great significance to actively seek and explore materials with good PT and TE performance to fully harvest infrared light energy. Here, we prepared an organic-inorganic hybrid bulk heterojunction film by combining poly(3,4-ethylene-dioxythiophene):polystyrenesulphonate (PEDOT:PSS) and ZnO nanowires (ZnO-NWs). This common composite strategy is able to utilize the ultra-wide spectrum ranging from ultraviolet-visible (UV-Vis) to near-infrared (NIR) light to realize light-to-electricity conversion based on the PTE effect. ZnO-NWs can not only increase the Seebeck coefficient of PEDOT:PSS, but also enhance the absorption of the hybrid film under the NIR light. Thereby, the enhancement of the photothermal-induced voltage was achieved due to the separation of generated electron-hole pairs in the built-in electric field induced by a photothermal gradient. This study provides a new suggestion for improving the PTE performance of the material and making better use of solar energy.

Tailoring the interface assembly of mesoporous TiO2 on BTO film toward high-performance UV photodetectors

A heterojunction film consisting of BaTiO3@mesoporous TiO2 was engineered via an interface assembly strategy and spin-coating to fabricate a highly efficient UV photodetector.

Engineering exposed vertical nano-TiO2 (001) facets/BiOI nanosheet heterojunction film for constructing a satisfactory PEC glucose oxidase biosensor.

In the field of photoelectrochemical (PEC) enzyme biosensors, constructing efficient photoelectrodes, in which the recombination of photogenerated carriers is an important factor affecting the performance, is of great significance. Herein, to enhance the separation efficiency of photogenerated carriers, titanium dioxide (TiO2) nanosheet (NS)/bismuth oxyiodide (BiOI) NS/glucose oxidase (GOx) composites were prepared via hydrothermal and solvothermal methods. Single-crystal anatase TiO2 NSs with a high percentage of (001) facets lead to better photocarrier separation due to heterojunctions between facets. After coupling with BiOI NSs, the photoelectrochemical performance of the electrode was greatly improved. The photogenerated electrons from TiO2 and BiOI gathered at TiO2 (101) and were exported through the fluorine-doped tin oxide (FTO) substrate to generate electrical signals. Photogenerated holes were transferred to TiO2 (001) and BiOI to participate in the enzymatic reaction, showing the outstanding separation of electrons and holes. The prepared TiO2 NS/BiOI NS/GOx glucose biosensor achieved satisfactory results, with sensitivity of 14.25 μA mM−1 cm−2, a linear measurement range of 0–1 mM, and a limit of detection (3S/N) of 0.01 mM in phosphate buffered saline (PBS) at a pH of 7.4. The mechanism for the efficient separation of photogenerated carriers based on the facet heterojunctions introduced in this paper also provides new insights into other optoelectronic biosensors.

Enhanced high-temperature energy storage properties of polymer composites by interlayered metal nanodots

The PC-Au nanodots-PC heterojunction film with merely 0.0035 vol% of Au nanodots exhibited a superior Ue (6.25 J cm−3) and η (86.6%) at 150 °C, far surpassing those of the reported advanced polymers and nanocomposite dielectrics.