Density Of Trap States Research Articles

The role of a highly optimized approach with superior transparent conductive oxide anode towards efficient organic solar cell

The effort emphasizes the numerical analysis of different transparent conducting oxides (TCOs) perspectives, which include ITO, FTO, AZO, and IZO anode-based organic solar cells (OSCs) with the drift-diffusion approach. The prior selection of aluminum-doped zinc oxide (AZO) as TCO is feasible for more extended transparency and antireflection due to a tailored absorption wavelength of <380 nm and the factors of higher mechanical flexibility, low-cost processing, and realistic performance at lower temperatures. To confirm the stability and reproducibility of the design OSC, the contribution of each interfacial layer thickness, i.e., AZO as TCOs, P3HT: PC61BM as an organic absorbing layer (OAL), Spiro-OMeTAD (SOT) as a hole-transport layer (HTL), and ZnO as an electron-transport layer (ETL), is also investigated. Furthermore, functions of optimum trap-state densities () and charge carrier mobility () in OAL have been performed to aid in increasing the diffusion length of excitons carriers (). These properties led to better photogeneration and transport of charge carriers, decreasing the series resistance (RS), leading to lower bimolecular recombination, a long carrier lifetime (), and consequently higher power conversion efficiency (PCE). The findings revealed that the proposed OSC structure achieves an excellent PCE of 10.28% for AZO as TCO with an 850 nm ultra-thick OAL under AM 1.5 G light irradiation. Hence, a better fabrication process for efficient OSC could also be improved by the optimization of all these critical factors for future research.

A passivation by H2O2-TiO2 interlayer for efficient and stable Carbon-based perovskite solar cells

A major challenge of carbon-based perovskite solar cells (C-PSCs) is boosting photovoltaic performance and stability. However, their performance can be limited by undesirable increases in trap states densities and nonradiative recombination caused by defects at the interface between the perovskite and the electron transporting layer (ETL) and in the bulk perovskite. Herein, a novel passivation using H2O2-TiO2 interlayer provides an effective approach to improve the interfacial bridging between TiO2 and perovskite in C-PSCs. Additionally, the surface morphology of the HT interlayer was elaborated by varying spin coating speeds of deposition. A suitable spin coating speed was found to be 3000 rpm, called TiO2/HT-3000 ETL. This allows lower oxygen vacancy within an interfacial layer and promotes high-quality growth of perovskite film with fewer grain boundaries. TiO2/HT-3000 ETL-based C-PSCs in a homemade air-filled dry glove box achieved a PCE of 16.23%, which improved the open-circuit voltage and fill factor values. These results can be attributed to effectively reduced trap state densities and nonradiative recombination losses in the device. In addition, the newly constructed TiO2/HT-3000 ETL can notably enhance the long-term stability in ambient air without encapsulation. This simple interface passivation strategy proposes a new path toward the commercialization of perovskite solar cells.

Thermally stable and efficient CsF-doped All-Inorganic CsPbIBr2 perovskite solar cells exceeding 15% PCE

Different strategies such as interface modification, cell encapsulation, perovskite doping, etc., are employed to address the different types of stability issues in perovskite solar cells. In this research, we used cesium fluoride (CsF) as a doping material to optimize the formation of CsPbIBr2 film and investigate its effect on the thermal stability of the devices. Our findings show that CsF diffuses into CsPbIBr2 seed film successfully and greatly enhances the stability of perovskite solar cells under study. Furthermore, compared to the reference device without doping, CsF-doped devices were found to have reduced trap state density, suppressed recombination of carriers, enhanced crystallinity, and improved power conversion efficiency from 13.15 to 15.54%. The study provides important pathways to fabricate highly stable perovskites thin films for all-in-organic solar cells.

Fabrication of perovskite solar cells with PCE of 21.84% in open air by bottom-up defect passivation and stress releasement

The archetypical n-type semiconductor material, tin oxide (SnO2), is common and well-known electron transport layer (ETL) material in regular perovskite solar cells (PSCs) due to the superior electron mobility and suitable energy level alignment with perovskite. However, plentiful detrimental defects concentrated at perovskite/SnO2 ETLs interface and unfavorable residual stress within perovskite films, compromise and dampen the photovoltaic performance and shelf stability of PSCs. Herein, alkali metal salts (i.e., 2, 2′-biquinoline-4, 4′-dicarboxylic acid alkali metal salts (BCA-2H, BCA-2Na, and BCA-2K)) are employed as pre-buried modifiers in SnO2 films to achieve a holistic amelioration of ETLs, perovskite photoactive layer, and their interface heterojunction. The BCA modification facilitates crystal orientation and crystalline of SnO2 nanocrystals, instrumental in decreasing trap state densities within functional layers, releasing interfacial residual tensile strain, and upgrading perovskite film performance. In comparison to BCA-2H- and BCA-2Na-doped ETLs, the BCA-2K decoration corroborate better defect passivation and stress release effect originating from preferable interface enhancement and desirable surface chemical properties. Consequently, the PSCs based on SnO2-BCA-2K ETL fabricated under open-air conditions deliver the champion efficiency of 21.84% accompanied by negligible hysteresis. Moreover, the unpacked devices maintain 81.2% of its original value after 1200 h storage under an ambient condition of 55 ± 5% (relative humidity, RH) and 25 ± 5 ℃ with open-circuit conditions.

C60-CN: A bifunctional interface modification material for perovskite solar cells

Titanium dioxide (TiO2) is regularly used as an electron transport material in n-i-p perovskite solar cells (PSCs). However, massive defects exist on the TiO2 surface, which will lead to serious hysteresis and interface charge recombination of the device, thus affecting the device’s efficiency. In this study, a cyano fullerene pyrrolidine derivative (C60-CN) was synthesized and applied to PSCs for the first time to modify the TiO2 electron transport layer. Systematic studies have shown that the addition of the C60-CN modification layer on the TiO2 surface will enlargement the perovskite grain size, improve the perovskite film quality, enhance electron transport, and reduce charge recombination. The C60-CN layer can significantly reduce the density of trap states in the perovskite solar cells. As a result, the PSCs based on C60-CN/TiO2 obtained a power conversion efficiency (PCE) of 18.60%, suppressing the hysteresis and improving the stability, whereas the PCE of the control device using the original TiO2 ETL was lower, 17.19%.

Modeling for ammonia gas concentration detection of GaN-based sensors

Excellent properties of gallium nitride (GaN) make it an ideal material for realizing gas sensors, especially for ammonia (NH[Formula: see text] detection. Although many researchers have pursued to describe the characteristics of GaN-based NH3 gas sensors by different approaches, few models have been reported. In this paper, with the consideration of the exponential distribution of interfacial states, a model for ammonia concentration detection of GaN gas sensors has been presented. The Poisson equation is applied to model the effect of defect states on the potential. By taking advantage of the current-voltage characteristics, the value of Schottky barrier height can be obtained. The concentration of the adsorbed NH3 gas is derived by exploiting the surface potential. It indicates that densities of acceptor interfacial trap states are in the order of 10[Formula: see text][Formula: see text]cm[Formula: see text]eV[Formula: see text]. The current increases with the NH3 concentration at the same applied voltage. In addition, detailed investigations of physical mechanisms and the analysis of the sensitivity have been depicted. It shows that the sensitivity followed an approximately exponential dependence on NH3 density. Results compared well with experimental data that verify the proposed model and simulation method.

Analysis of trap distribution and NBTI degradation in Al2O3/SiO2 dielectric stack

In this work, p-substrate MOS capacitors with plasma-enhanced atomic-layer-deposited Al2O3/ thermally-grown SiO2 dielectric stack (with a target equivalent oxide thickness of 4.2 nm) are investigated by means of the conductance method in a temperature range from 25 °C to 150 °C. The trap state density and energy level distribution in the silicon bandgap are extracted over the bandgap. Furthermore, negative bias temperature instability is analyzed by two-point capacitance–voltage characterization to evaluate the electrical stability and dielectric reliability of the Al2O3/SiO2 stack. The contributions from interface and oxide trap generations are detailed. Our results indicate that plasma-enhanced atomic layer deposited Al2O3 on thermal SiO2 stack features low interface trap density, and comparable dielectric reliability to conventional SiO2, SiOxNy, and high-k dielectric stacks.

Performance improvement of GaN-based microdisk lasers by using a PEALD-SiO2 passivation layer.

Dry-etching is often utilized to shape GaN-based materials. However, it inevitably causes plenty of sidewall defects as non-radiative recombination centers and charge traps that deteriorate GaN-based device performance. In this study, the effects of dielectric films deposited by plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) on GaN-based microdisk laser performance were both investigated. The results demonstrated that the PEALD-SiO2 passivation layer largely reduced the trap-state density and increased the non-radiative recombination lifetime, thus leading to the significantly decreased threshold current, notably enhanced luminescence efficiency and smaller size dependence of GaN-based microdisk lasers as compared with the PECVD-Si3N4 passivation layer.

Enhancement of Stability in n-Channel OFETs by Modulating Polymeric Dielectric.

In this study, a high-K material, aluminum oxide (AlOx), as the dielectric of organic field-effect transistors (OFETs) was used to reduce the threshold and operating voltages, while focusing on achieving high-electrical-stability OFETs and retention in OFET-based memory devices. To achieve this, we modified the gate dielectric of OFETs using polyimide (PI) with different solid contents to tune the properties and reduce the trap state density of the gate dielectric, leading to controllable stability in the N, N'-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13)-based OFETs. Thus, gate field-induced stress can be compensated for by the carriers accumulated due to the dipole field created by electric dipoles within the PI layer, thereby improving the OFET's performance and stability. Moreover, if the OFET is modified by PI with different solid contents, it can operate more stably under fixed gate bias stress over time than the device with AlOx as the dielectric layer only can. Furthermore, the OFET-based memory devices with PI film showed good memory retention and durability. In summary, we successfully fabricated a low-voltage operating and stable OFET and an organic memory device in which the memory window has potential for industrial production.

Understanding the influence of Cu ions implantation towards highly efficient MAPbBr3 perovskite solar cells

MAPbBr3 films were deposited on FTO-glass substrates by the spin coating technique. These films were irradiated by Cu ions with a flounce rate of 2×1014 ions/cm2, 4×1014 ions/cm2, and 6×1014 ions/cm2 respectively. MAPbBr3 films exhibited a crystalline nature and a cubic structure, as verified by XRD. The MAPbBr3 film irradiated by 4×1014 ions/cm2 Cu ions has a large grain size (33 nm) and a small Eg (2.11 eV). As a result, the trap-state densities within the perovskite bulk were suppressed at interfaces as well as in the bulk material for smooth and improved carrier transportation. The calculated valence and conduction band edges of MAPbBr3 are ‘-5.60’ and ‘-3.2’, respectively. The film exposed to Cu ions has the CB edge pushed towards the lower value, making it a preferable solar cell material. The non-irradiated and irradiated films by Cu ions have higher carrier life times of 63 ns and 74 ns, respectively. The cell fabricated with ions/cm2 Cu ions-MAPbBr3 film displayed a champion device with FF (0.84), Jsc (9.34 mA-cm−2), Voc (1.098), and PCE (8.59%).

Centimeter-Sized Single Crystals of Dion-Jacobson Phase Lead-Free Double Perovskite for Efficient X-ray Detection.

2D Dion-Jacobson (DJ) phase hybrid perovskites have shown great promise in the photoelectronic field owing to their outstanding optoelectronic performance and superior structural rigidity. However, DJ phase lead-free double perovskites are still a virgin land with direct X-ray detection. Herein,wehave designed and synthesized a new DJ phase lead-free layered double perovskite of (HIS)2 AgSbBr8 (1, HIS2+ = histammonium). Centimeter-sized (18 × 10 × 5 mm3 ) single crystals of 1 are successfully grown via the temperature cooling technique, exhibiting remarkable semiconductive characteristics such as a high resistivity (2.2 × 1011 Ω cm), a low trap state density (3.56 × 1010 cm-3 ), and a large mobility-lifetime product (1.72 × 10-3 cm2 V-1 ). Strikingly, its single-crystal-based X-ray detector shows a high sensitivity of 223 µC Gy-1 air cm-2 under 33.3V mm-1 , a low detection limit (84.2 nGyair s-1 ) and superior anti-fatigue. As far asweknow,wefirstly demonstrates the potential of 2D DJ phase lead-free hybrid double perovskite in X-ray detection, showing excellent photoelectric response and operational stability. This work will pave a promising pathway to the innovative application of hybrid perovskites for eco-friendly and efficient X-ray detection.

Tetrachromatic vision-inspired neuromorphic sensors with ultraweak ultraviolet detection

Sensing and recognizing invisible ultraviolet (UV) light is vital for exploiting advanced artificial visual perception system. However, due to the uncertainty of the natural environment, the UV signal is very hard to be detected and perceived. Here, inspired by the tetrachromatic visual system, we report a controllable UV-ultrasensitive neuromorphic vision sensor (NeuVS) that uses organic phototransistors (OPTs) as the working unit to integrate sensing, memory and processing functions. Benefiting from asymmetric molecular structure and unique UV absorption of the active layer, the as fabricated UV-ultrasensitive NeuVS can detect 370 nm UV-light with the illumination intensity as low as 31 nW cm−2, exhibiting one of the best optical figures of merit in UV-sensitive neuromorphic vision sensors. Furthermore, the NeuVS array exbibits good image sensing and memorization capability due to its ultrasensitive optical detection and large density of charge trapping states. In addition, the wavelength-selective response and multi-level optical memory properties are utilized to construct an artificial neural network for extract and identify the invisible UV information. The NeuVS array can perform static and dynamic image recognition from the original color image by filtering red, green and blue noise, and significantly improve the recognition accuracy from 46 to 90%.

Research on the β-Ga2O3 Schottky barrier diodes with oxygen-containing plasma treatment

This Letter reports two kinds of oxygen-containing plasma treated β-Ga2O3 Schottky barrier diodes (SBDs), including N2O plasma treatment and O2 plasma treatment, and the SBD without plasma is prepared for comparison. I–V characteristics, breakdown characteristics, and trap state characteristics of three devices have been studied. It is found that the turn-on voltage of SBDs with N2O plasma can reduce to 0.6 V, and the better current density of 750 A/cm2 and an on-resistance of 3.5 mΩ cm2 are obtained after the N2O plasma treatment. Moreover, the breakdown voltage of SBDs with N2O plasma is 50.2% higher than the conventional one, whose value reaches 323 V. In addition, the trap states' characteristics of the devices are studied, which show that the oxygen-containing plasma can reduce the deep level trap states density partly in the anode region, which can improve the surface quality effectively.

Ferroelectric dipole-MAPbI3 coupled x-ray detector

Blade coating offers a low-cost production method for fabricating perovskite thick-film x-ray detectors. However, due to the preferential nucleation at the gas–liquid interface of a perovskite solution, high-quality perovskite thick films are in such a dilemma, sacrificing either the density of the thick film by forming a porous structure or the thickness of the film through depositing a compact structure. The porous structure will lead to carrier recombination and ion migration while low thickness will cause insufficient x-ray absorption, which will increase the dark current or reduce the sensitivity of the corresponding x-ray detector. In the present work, a scalable ferroelectric dipole–methylamine lead iodide (MAPbI3) coupled x-ray detector is proposed, where the x-ray photoconductor in situ formed on indium tin oxide shows a dense fibrous mesoscopic structure oriented along the charge-carriers transport direction. It is demonstrated that ferroelectric dipoles promise not only strong coupling effects with MAPbI3, driving better crystallinity and denser assemblies, but also excellent passivation to MAPbI3 interfaces, decreasing trap-state densities, leading to improved direct x-ray detection performance. In addition, the enhanced operational stability of the corresponding device suggests a strategy of introducing the localized polarization field for stable perovskite direct x-ray detectors.

High‐Quality CsAg2I3Microwires Grown by Spatial Confinement Method for Self‐Powered UV Photodetectors

AbstractRecently, lead halide perovskites arouse intensive attentions in photoelectric fields owing to their low trap state density, high carrier mobility, large extinction coefficient, and low‐temperature solution processing technique. However, their future commercial development is severely hampered by the lead toxicity and instability. Although lead‐free metal‐halide perovskites recently have been extensively studied in optoelectronics, their low‐dimensional counterparts can further expand their novel optical and electronic properties for potential applications. In this work, the planar growth of one‐dimensional (1D) CsAg2I3 single‐crystal microwires (MWs) on diverse substrates by space‐confined method is reported. The growth kinetic process of CsAg2I3 single‐crystal MWs is elucidated by in situ observation. Furthermore, the CsAg2I3 single‐crystal MWs exhibit potential applications in ultraviolet light photodetectors as a photoactive layer. The fabricated heterojunction photodetector exhibits pronounced photoelectric performances working in self‐powered mode, including a specific detectivity of 2.09 × 108 Jones, a high responsivity of 26.5 mA W−1, and fast response speed of 258.43/289.32 ms under light illumination of 265 nm, due to the high crystallinity and effective photogenerated carrier transfer. This study provides a vital insight into the rational design of low‐dimensional perovskites for versatile optoelectronic applications.

Finely Tuned Molecular Packing Realized by a New Rhodanine-Based Acceptor Enabling Excellent Additive-Free Small- and Large-Area Organic Photovoltaic Devices Approaching 19 and 12.20% Efficiencies.

A new nonfullerene acceptor (NFA), BTA-ERh, was synthesized and integrated into a PM6:Y7:PC71BM ternary system to regulate the blend film morphology for enhanced device performance. Due to BTA-ERh's good miscibility with host active blend films, an optimized film morphology was obtained with appropriate phase separation and fine-tuning of film crystallinity, which ultimately resulted in efficient exciton dissociation, charge transport, lower recombination loss, and decreased trap-state density. The resulting additive-free quaternary devices achieved a remarkable efficiency of 18.90%, with a high voltage, fill factor, and current density of 0.87 V, 76.32%, and 28.60 mA cm-2, respectively. By adding less of a new small molecule with high crystallinity, the favorable nanomorphology shape of blend films containing NFAs might be adjusted. Consequently, this strategy can enhance photovoltaic device performance for cutting-edge NFA-based organic solar cells (OSCs). In contrast, the additive-free OSCs exhibited good operational stability. More importantly, large-area modules with the quaternary device showed a remarkable efficiency of 12.20%, with an area as high as 55 cm2 (substrate size, 100 cm2) in an air atmosphere via D-bar coating. These results highlight the enormous research potential for a multicomponent strategy for future additive-free OSC applications.

Inkjet‐Printing Controlled Phase Evolution Boosts the Efficiency of Hole Transport Material Free and Carbon‐Based CsPbBr3 Perovskite Solar Cells Exceeding 9%

Hole transport material free carbon‐based all‐inorganic CsPbBr3 perovskite solar cells (PSCs) are promising for commercialization due to its low‐cost, high open‐circuit voltage (Voc) and superior stability. Due to the different solubility of PbBr2 and CsBr in conventional solvents, CsPbBr3 films are mainly obtained by multi‐step spin‐coating through the phase evolution from PbBr2 to CsPb2Br5 and then to CsPbBr3. The scalable fabrication of high‐quality CsPbBr3 films has been rarely studied. Herein, an inkjet‐printing method is developed to prepare high‐quality CsPbBr3 films. The formation of long‐range crystalline CsPb2Br5 phase can effectively improve phase purity and promote regular crystal stacking of CsPbBr3. Consequently, the inkjet‐printed CsPbBr3 C‐PSCs realized PCEs up to 9.09%, 8.59% and 7.81% with active areas of 0.09, 0.25, and 1 cm2, respectively, demonstrating the upscaling potential of our fabrication method and devices. This high performance is mainly ascribed to the high purity, strong crystal orientation, reduced surface roughness and lower trap states density of the as‐printed CsPbBr3 films. This work provides insights into the relationship between the phase evolution mechanisms and crystal growth dynamics of cesium lead bromide halide films.

Construction of a 3D/2D heterojunction based on a fluorinated cyclohexylamine 2D Ruddlesden–Popper perovskite for highly efficient and stable perovskite solar cells

Nonradiative recombination at perovskite/charge transport layer interfaces is caused by surface defects and instability, and it is known to limit the long-term development of perovskite solar cells (PSCs). To overcome this issue, the three-dimensional/two-dimensional (3D/2D) perovskite heterojunction has emerged as a possible solution to improve the stabilities and efficiency of PSCs. Herein, we employ a simple one-step method to prepare n-i-p-structured PSCs using a 3D/2D perovskite heterojunction as the absorption layer. For this purpose, the large and non-centrosymmetric 4,4-difluorocyclohexylammonium (DFCHA+) cation, which has been confirmed to be a valid organic spacer in 2D Ruddlesden–Popper (RP) phase perovskites, is employed as an organic ligand for post-treatment of the surfaces of MAPbI3 films. The presence of an ultrathin 2D RP phase perovskite was confirmed on the surface, and the 3D/2D perovskite heterojunction was successfully constructed. Benefitting from surface post-treatment, the density of the surface trap states was reduced with effective passivation. In addition, nonradiative recombination was suppressed, and the interface bands were aligned. As a result, the optimal device achieved a power conversion efficiency of 21.93% with a remarkable open-circuit voltage (VOC) of 1.14 V, a current density (JSC) of 23.71 mA cm−2, and a fill factor of 0.82. Furthermore, owing to the hydrophobicity of the DFCHA+ cation, the unencapsulated device was able to maintain an initial efficiency of 82.3% after storage for 500 h at a relative humidity of ∼45%. We believe that this post-treatment strategy has wide application potential in the field of photovoltaic devices.

Improved Thermal Stability and Film Uniformity of Halide Perovskite by Confinement Effect brought by Polymer Chains of Polyvinyl Pyrrolidone.

Polyvinyl pyrrolidone (PVP) is doped to PbI2 and organic salt during two-step growth of halideperovskite. It is observed that PVP molecules can interact with both PbI2 and organic salt, reduce the aggregation and crystallization of the two, and then slow down the coarsening rate of perovskite. As doping concentration increases from 0 to 1mM in organic salt, average crystallite size of perovskite decreases monotonously from 90 to 34nm; Surface fluctuation reduces from 259.9 to 179.8nm at first, and then increases; Similarly, surface roughness decreases from 45.55 to 26.64nm at first, and then rises. Accordingly, a kind of "confinement effect" is resolved to crystallite growth and surface fluctuation/roughness, which helps to build compact and uniform perovskite film. Density of trap states (t-DOS) is cut down by ≈60% at moderate doping (0.2mM). Due to the "confinement effect", power conversion efficiencyof perovskite solar cellsis improved from 19.46 (±2.80) % to 21.50 (±0.99) %, and further improved to 24.11% after surface modification. Meanwhile, "confinement effect" strengthens crystallite/grain boundaries and improves thermal stability of both film and device. T80 of device increases to 120h, compared to 50h for reference ones.

Origin of Hole‐Trapping States in Solution‐Processed Copper(I) Thiocyanate and Defect‐Healing by I2 Doping

AbstractSolution‐processed copper(I) thiocyanate (CuSCN) typically exhibits low crystallinity with short‐range order; the defects result in a high density of trap states that limit the device's performance. Despite the extensive electronic applications of CuSCN, its defect properties are not understood in detail. Through X‐ray absorption spectroscopy, pristine CuSCN prepared from the standard diethyl sulfide‐based recipe is found to contain under‐coordinated Cu atoms, pointing to the presence of SCN− vacancies. A defect passivation strategy is introduced by adding solid I2 to the processing solution. At small concentrations, the iodine is found to exist as I− which can substitute for the missing SCN− ligand, effectively healing the defective sites and restoring the coordination around Cu. Computational study results also verify this point. Applying I2‐doped CuSCN as a p‐channel in thin‐film transistors shows that the hole mobility increases by more than five times at the optimal doping concentration of 0.5 mol.%. Importantly, the on/off current ratio and the subthreshold characteristics also improve as the I2 doping method leads to the defect‐healing effect while avoiding the creation of detrimental impurity states. An analysis of the capacitance‐voltage characteristics corroborates that the trap state density is reduced upon I2 addition.