Light-absorbing Layer Research Articles

Graphene/AlGaN Schottky barrier photodiodes and its application for array devices

This study evaluated the characteristics of graphene/AlGaN Schottky barrier photodiodes using graphene as a transparent electrode film and AlGaN as a light-absorbing sensor layer. It was found that the Schottky barrier height of graphene/AlGaN ranged within 1.2–1.7 eV depending on the Al composition ratio. By forming an array of photodiodes, an 8 × 8 pixels ultraviolet image sensor was fabricated.

Visible-light photoelectric performance of RMnO3 (R = La, Pr and Nd) epitaxial films with structural distortion

All-inorganic perovskite has aroused extensive attention as the light absorption layer of solar cells due to the high photoelectric conversion efficiency and chemical stability. In this work, RMnO3 (RMO, R = La, Pr and Nd)/(001) LaAlO3 (LAO) epitaxial films were prepared by the polymer assisted deposition method. All of the RMO films were grown epitaxially with tetragonal distortion (like Jahn-Taller distortion) of MnO6 octahedron. Owing to lattice mismatch between RMO and LAO, the tetragonal distortion of MnO6 octahedron increases when the radius of trivalent R ions increases. This reduces the crystal field splitting energy of MnO6 octahedron, resulting in a reduction in the band gap and enhancement of the visible-light photoelectric performance. It also reveals that the surface-adsorbed oxygen plays a crucial role in the photoelectric process of the RMO epitaxial films. More surface-adsorbed oxygen, existing in RMO films with larger R ions, can enhance the double exchange of electrons in Mn3+ - O2− - Mn4+, thus preventing the recombination of photogenerated electron-hole pair and improving the photoelectric performance. These results provide a channel to tune the structure and photoelectric performance of perovskite manganese oxide.

Atomic-scale platinum deposition on photocathodes by multiple redox cycles under illumination for enhanced solar-to-hydrogen energy conversion

The fabrication of photoelectrochemical (PEC) cells using Cu2O, a semiconductor light absorber that responds to infinite sunlight, requires techniques for loading and activating highly efficient cocatalysts to increase the hydrogen production selectivity. However, there has been relatively little interest in techniques for the deposition of efficient catalysts on PEC electrodes that can maximize the surface activation of the light absorption layer for water splitting, because precise control of the Pt loading at the atomic scale is difficult. We designed an intelligent multiple-redox illuminated deposition technique capable of depositing atomic-scale Pt catalysts with optimal performance on the photocathode surface. An Sb:Cu2O/Cu2O/Al:ZnO/TiO2 photocathode with the proposed atomic-scale Pt catalyst has a high photocurrent density of 6.2 mA cm−2 and a more positive onset potential of 0.71 VRHE. In addition, the mass activity of this electrode is 3.35 times higher than that of Pt samples deposited by conventional methods, and the electrode also shows outstanding operational stability. The proposed approach enables a uniform catalyst distribution and position-selective deposition atomic-scale Pt by repeated redox reactions. Consequently, our proposal enables the simultaneous realization of enhanced conversion efficiency and low cost by the consumption of a relatively small quantity of Pt in controllable redox photodeposition.

A Study on UVC Photodetector Using Mixed-Cation Perovskite with High Detection Rate as Light-Absorption Layer.

In this study, a mixed-cation perovskite ultraviolet (UV) C photodetector was fabricated using a simple formamidinium iodide (FAI) post-treatment process. The fabricated device uses FAxMA1−xPbI3 perovskite as a light-absorption layer and SnO2, which has high transmittance in the UVC wavelength region, as an electron-transport layer. The fabricated device exhibited a response of 50.8 mA/W, detectability of 4.47 × 1013 Jones, and external quantum efficiency of 53%. Therefore, the approach used in this study is promising for many applications in the UVC wavelength region.

Methylammonium thiocyanate seeds assisted heterogeneous nucleation for achieving high-performance perovskite solar cells

Thiocyanate (SCN-) has been reported to manage crystallization of perovskite films and improve their optoelectronic properties in solar cells. However, the mechanism of SCN- in preparation of high-quality (MAFA)Pb(IBr)3 based light-absorbing layers has not been well investigated yet. In this work, we investigate the effects of SCN- on phase transition of (MAFA)Pb(IBr)3 perovskite films and the corresponding device performance by introducing methylammonium thiocyanate (MASCN) in a PbI2 precursor solution which is used to make perovskite by a two-step sequential deposition method. Characterization of the perovskite films has shown that a proper amount (1 mg/mL) of MASCN in PbI2 can produce PbI2-MASCN seeds which act as a nucleation center for assisting heterogeneous nucleation of the (MAFA)Pb(IBr)3. Meanwhile, MASCN helps to effectively control crystallization of the perovskite film by obtaining preferential crystal growth orientation. Furthermore, MASCN is beneficial to eliminate residual PbI2 and prepare perovskite films with low trap-state density. Consequently, the power conversion efficiency (PCE) of the perovskite solar cells increases from 18.36% to 20.4%. An enhanced device stability against moisture is also observed in the MASCN-treated device which exhibits 90% retention of the initial efficiency after exposed to the ambient air for 1780 h.

Efficient and Stable FA‐Rich Perovskite Photovoltaics: From Material Properties to Device Optimization

AbstractThe perovskite photovoltaic field has developed rapidly within a decade. In particular, formamidinium (FA)‐rich perovskite allows a broad absorption spectrum, and is considered to be one of the most promising perovskite materials. Great progress has been achieved, and most recorded high‐efficient perovskite solar cells (PSCs) used the FA‐rich perovskite light absorption layer. However, the black α‐phase formamidinium lead iodide (FAPbI3) perovskite easily transforms into an undesirable δ‐phase at a low temperature. Thus, researchers have put a lot of effort into deeply understanding the phase transformation and stabilization mechanism of FA‐rich perovskite. Herein, the fundamental physical properties of FAPbI3 materials, including crystal structure, phase‐transition temperature, charge‐carrier dynamics, etc. are summarized, and establish a complete phase evolution with temperature by reviewing previous reports. The intrinsic and external factors are subsequently discussed for influencing the stability of FAPbI3 perovskite and the remarkable breakthroughs of FA‐rich PSCs in recent years are reviewed. Moreover, a series of strategies to stabilize FA‐rich perovskite is summarized, including but not limited to compositional engineering, passivating engineering, processing engineering, and strain engineering. Finally, several new viewpoints are provided for improving the efficiency and stability of PSCs. This review may be regarded as a reference project for preparing high‐efficient and stable perovskite photovoltaic devices.

High-performance floating-gate organic phototransistors based on n-type core-expanded naphthalene diimides

In the field of organic phototransistor, achieving both broad-spectral and high photosensitivity has always been a big challenge. The innovation of device structure has previously proven to be a possible solution to this problem. Here in this study, a novel organic phototransistor based on a high mobility n-type small molecule as the conducting layer and an isolated bulk heterojunction light-absorbing layer as the floating gate has been demonstrated in this study. With the special designed device structure, the phototransistor shows extremely high sensitivity to broad spectral and weak light irradiation, and the photoresponsivity and photocurrent/dark-current ratio of the device can reach up to 4840 mA/W and 1.8 × 105 respectively. For conclusion, this study suggests a potential way to obtain high-performance phototransistors at room temperature, which will further promote the commercial application of organic phototransistors.

Large-area photonic lift-off process for flexible thin-film transistors

Fabricating flexible electronics on plastic is often limited by the poor dimensional stability of polymer substrates. To mitigate, glass carriers are used during fabrication, but removing the plastic substrate from a carrier without damaging the electronics remains challenging. Here we utilize a large-area, high-throughput photonic lift-off (PLO) process to rapidly separate polymer films from rigid carriers. PLO uses a 150 µs pulse of broadband light from flashlamps to lift-off functional thin films from glass carrier substrates coated with a light absorber layer (LAL). Modeling indicates that the polymer/LAL interface reaches above 800 °C during PLO, but the top surface of the PI remains below 120 °C. An array of indium zinc oxide (IZO) thin-film transistors (TFTs) was fabricated on a polyimide substrate and photonically lifted off from the glass carrier. The TFT mobility was unchanged by PLO. The flexible TFTs were mechanically robust, with no reduction in mobility while flexed.

Rational construction of S-doped FeOOH onto Fe2O3 nanorods for enhanced water oxidation

Hematite-based photoanode (α-Fe2O3) is considered the promising candidate for photoelectrochemical (PEC) water splitting due to its relatively small optical bandgap. However, severe charge recombination in the bulk and poor surface water oxidation kinetics have limited the PEC performance of Fe2O3 photoelectrodes, which is far below the theoretical value. Herein, a new catalyst, S-doped FeOOH (S-FeOOH), has been immobilized onto the surface of the Fe2O3 nanorod (NR) array by a facile chemical bath deposition incorporated thermal sulfuration process. The grown S-FeOOH layer acts not only as an efficient catalyst layer to accelerate the water oxidation on the surface of photoelectrode but also constructs a heterojunction with the light absorption layer to facilitate the interface charge carrier separation and transfer. As expected, the modified S-FeOOH@Fe2O3 photoanode achieves a remarkable increase in PEC performance of 2.30 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (VRHE) andan apparent negative shifted onset potential of 250 mV in comparison with pristine Fe2O3 (0.95 mA cm−2 at 1.23 VRHE). These results provide a simple and effective strategy to coupling oxygen evolution catalysts with photoanodes for practically high-performance PEC applications.

Compact SnO2/Mesoporous TiO2 Bilayer Electron Transport Layer for Perovskite Solar Cells Fabricated at Low Process Temperature.

Charge transport layers have been found to be crucial for high-performance perovskite solar cells (PSCs). SnO2 has been extensively investigated as an alternative material for the traditional TiO2 electron transport layer (ETL). The challenges facing the successful application of SnO2 ETLs are degradation during the high-temperature process and voltage loss due to the lower conduction band. To achieve highly efficient PSCs using a SnO2 ETL, low-temperature-processed mesoporous TiO2 (LT m-TiO2) was combined with compact SnO2 to construct a bilayer ETL. The use of LT m-TiO2 can prevent the degradation of SnO2 as well as enlarge the interfacial contacts between the light-absorbing layer and the ETL. SnO2/TiO2 bilayer-based PSCs showed much higher power conversion efficiency than single SnO2 ETL-based PSCs.

Composition engineering to enhance the photovoltaic performance and to prolong the lifetime for silver bismuth iodide solar cell

Lead, a toxic element in organometal halide perovskite solar cells, has caught lots of attention and has raised public concerns after such perovskite solar cells made rapid progress in their photovoltaic performance. Herein, a series of lead-free light absorber layers with a rudorffite structure were examined in this study. The obscure role of A-site and B-site cation in silver bismuth iodide rudorffite materials has been revealed through their energy diagrams and surface potential analyses. By manipulating the stoichiometric ratio of bismuth and silver at a ratio of 1.1/3, a Ag3BiI6 layer with uniform morphology, high carrier mobility, and a high light response was obtained. The superior optoelectrical properties of the modified Ag3BiI6 active layer directly influenced the photovoltaic performance and the environmental stability of such a device. The photovoltaic device with the modified Ag3BiI6 active layer exhibited a PCE of 2.60%. It also maintained over 80% of its initial PCE after being stored in an ambient environment for over 3,000 h. This result sheds light on how to process silver bismuth iodide materials and extends the knowledge for rudorffite materials.

Two-Dimensional Cs2AgBiBr6/WS2 Heterostructure-Based Photodetector with Boosted Detectivity via Interfacial Engineering.

Two-dimensional (2D) transition metal dichalcogenide (TMDC) monolayers have been widely used for optoelectronic devices because of their ultrasensitivity to light detection acquired from their direct gap properties. However, the small cross-section of photon absorption in the atomically thin layer thickness significantly limits the generation of photocarriers, restricting their performance. Here, we integrate monolayer WS2 with 2D perovskites Cs2AgBiBr6, which serve as the light absorption layer, to greatly enhance the photosensitivity of WS2. The efficient charge transfer at the Cs2AgBiBr6/WS2 heterojunction is evidenced by the shortened photoluminescence (PL) decay time of Cs2AgBiBr6. Scanning photocurrent microscopy of Cs2AgBiBr6/WS2/graphene reveals that improved charge extraction from graphene leads to an enhanced photoresponse. The 2D Cs2AgBiBr6/WS2/graphene vertical heterostructure photodetector exhibits a high detectivity (D*) of 1.5 × 1013 Jones with a fast response time of 52.3 μs/53.6 μs and an on/off ratio of 1.02 × 104. It is worth noting that this 2D heterostructure photodetector can realize self-powered light detection behavior with an open-circuit voltage of ∼0.75 V. The results suggest that the 2D perovskites can effectively improve the TMDC layer-based photodetectors for low-power consumption photoelectrical applications.

Effect of Annealing in ITO Film Prepared at Various Argon-and-Oxygen-Mixture Ratios via Facing-Target Sputtering for Transparent Electrode of Perovskite Solar Cells

Normal perovskite solar cells (PSCs) consist of the following layers: transparent electrode, electron-transport layer (ETL), light-absorbing perovskite layer, hole-transport layer (HTL), and metal electrode. Energy, such as electricity, is produced through light absorbance and electron–hole generation/transport between two electrode types (metal film and transparent conducting film). Among stacked layers in a PSC, the transparent electrode plays the high-performance-power-conversion-efficiency role. Transparent electrodes should have high-visible-range transparency and low resistance. Therefore, in this study, we prepared indium tin oxide (ITO) films on a glass substrate by using facing-target sputtering without substrate heating treatment and investigate the heating-treatment effect on the ITO-film properties for perovskite solar cells (PSCs). Moreover, we fabricated PSCs with ITO films prepared at various oxygen flows during the sputtering process, and their energy-conversion properties are investigated.

Photothermal trap with multi-scale micro-nano hierarchical structure enhances light absorption and promote photothermal anti-icing/deicing

Facing climate change caused by carbon emissions and the disaster of ice accumulation on outdoor equipment, the large-scale use of solar energy is a promising solution. Here, a photothermal anti-icing material composed of substrate, carbon-based light-absorption layer, and encapsulation layer was prepared using a combined template-spraying method. The multi-scale micro-nano hierarchical structure can enhance light absorption in a limited space due to the light trapping effect, which was confirmed by ray-tracing simulation and the UV–vis-NIR light absorption result, and the average light absorption rate is up to ∼ 98% at the 200–2000 nm wavelength. The average surface temperature can reach ∼ 85 °C under 1 sun (qi = 100 mW/cm2) illumination at room temperature (Tr = 25 °C), and the photo-to-thermal conversion efficiency is up to 60.76%. Excellent photothermal conversion performance endows the material with the ability of photothermal deicing, and the frost or ice layer can melt and fall off from the surface after 300 s of 1 sun illumination. Besides, the photothermal anti-icing experiments under 1 sun illumination show that the prepared material has a lower freezing temperature (-25.20 ± 1.34 °C), a longer freezing delay time (774.76 ± 114.19 s), and a heat transfer model during the icing process was proposed. Surface friction, water flow impact, and solution immersion tests show that the material has excellent mechanical durability and chemical stability. The materials prepared in this work show enormous application potential on outdoor equipment due to the simple preparation method, strong mechanical durability, and excellent photothermal anti-icing/deicing properties.

Design and performance boost of a MOF-functionalized-wood solar evaporator through tuning the hydrogen-bonding interactions

Interfacial solar evaporation technology is recognized as one of the most promising strategies to address freshwater scarcity issues. To realize the sustainability of this technology for producing potable water from seawater and contaminated water sources, multi-functional photothermal materials need to be explored to attain higher vapor output at the same solar energy input. Herein, a novel wood-based solar evaporator composed of porous wood substrate, zeolitic imidazolate framework-8 (ZIF-8), and polydopamine (PDA) as a light absorption layer is developed. The in-situ loading of ZIF-8 in the microchannels renders the wood evaporator an important function of reducing the equivalent evaporation enthalpy due to the lowered hydrogen bonding density of water molecules when they pass the wood channels, substantially augmenting solar evaporation efficiency. A superior evaporation rate of 2.70 kg m−2 h−1 is achieved under 1.0 sun irradiation, which exceeds the theoretical limit of a typical 2D photothermal evaporator (~1.46 kg m−2 h−1). The designed wood/ZIF-8@PDA also exhibits a prominent removal efficiency for harmful ions and organic pollutants. This multifunctional wood-based solar evaporator shows great potential for future freshwater production.

Effects of annealing following back contact metal layer formation on CZTS solar cell properties

Cu2ZnSnS4 (CZTS) is interesting as a light absorption layer for thin-film solar cells because it consists of only earth-abundant materials such as copper, zinc, tin, and sulfur. The poor adhesion between CZTS and molybdenum (Mo), which is the back metal contact material, causes CZTS to peeling off during the chemical bath deposition (CBD) for the formation of CdS as a buffer layer. This induces severe degradation of the solar cell performance. In this study, we investigated the effect of annealing following back contact metal layer formation on CZTS stability and solar cell performance. By annealing Mo/soda lime glass at 400 °C in atmosphere, Mo was oxidized, and the surface roughness of Mo increased. On the Mo surface, the CZTS peeling off was suppressed during the CBD process, resulting in an improvement in the shunt resistance.

High-Performance 3D Vertically Oriented Graphene Photodetector Using a Floating Indium Tin Oxide Channel.

Vertically oriented graphene (VG), owing to its sharp edges, non-stacking morphology, and high surface-to-volume ratio structure, is promising as a consummate material for the application of photoelectric detection. However, owing to high defect and fast photocarrier recombination, VG-absorption-based detectors inherently suffer from poor responsivity, severely limiting their viability for light detection. Herein, we report a high-performance photodetector based on a VG/indium tin oxide (ITO) composite structure, where the VG layer serves as the light absorption layer while ITO works as the carrier conduction channel, thus achieving the broadband and high response nature of a photodetector. Under the illumination of infrared light, photoinduced carriers generated in VG could transfer to the floating ITO layer, which makes them separate and diffuse to electrodes quickly, finally realizing large photocurrent detectivity. This kind of composite structure photodetector possesses a room temperature photoresponsivity as high as ~0.7 A/W at a wavelength of 980 nm, and it still maintains an acceptable performance at temperatures as low as 87 K. In addition, a response time of 5.8 s is observed, ~10 s faster than VG photodetectors. Owing to the unique three-dimensional morphology structure of the as-prepared VG, the photoresponsivity of the VG/ITO composite photodetector also presented selectivity of incidence angles. These findings demonstrate that our novel composite structure VG device is attractive and promising in highly sensitive, fast, and broadband photodetection technology.

Method for improving electrical property of polysilicon film used to light absorption layer of photodetector

Method for improving electrical property of polysilicon film used to light absorption layer of photodetector

Cr2O3 interlayer at TiO2/perovskite interface propelling the efficiency improvement of perovskite solar cells

In perovskite solar cells, charge loss and carrier recombination at interfaces are crucial factors to photovoltaic performance. In this report, Cr2O3 layer is introduced between TiO2 electron transport layer and perovskite light-absorption layer. The modified device achieves an improved power conversion efficiency of 18.51% compared to the value of 17.10% for the control device. For one thing, the enhanced photovoltaic performance can be attributed to the cascade conduction band structure of TiO2/Cr2O3 bilayer. Cr2O3 is a kind of wide bandgap semiconductor. Its energy level matches very well with TiO2 ETL and perovskite light-absorption layer so as to it can work as a barrier to retard electrons from TiO2 layer reversely transport, impeding charge carrier recombination. For another, Cr2O3 interface layer can effectively avoid the direct contact of perovskite and bottom conductive electrode, reducing current leakage and carrier recombination. Both of these advantages lead to better photovoltaic performance. The work exhibits that Cr2O3 can be an efficacious interlayer material in perovskite solar cells.

Preparation of Cu2SnS3 thin film by sol-gel dip coating

Cu2SnS3 (CTS), an environmentally friendly semiconductor material that has little impact on the human body, was developed as an alternative material to silicon-based solar cells, which are currently the mainstream product in the solar cell market. In this study, by adopting the sol-gel dip coating method, a CTS thin film was produced at low cost without using a vacuum process for use as a solar cell light absorption layer. CTS thin films were prepared while varying the annealing temperature and the amount of α-cyclodextrin added, and the results were compared by different evaluation methods. In addition, the samples to which α-cyclodextrin was added showed peaks due to CTS at (112) and (220) in all the samples. The crystallinity was not found to depend on the amount of α-cyclodextrin added.