Density Of Trap States Research Articles

Grain Size-Engineering of PbS Colloidal Quantum Dots-Based NO2Gas Sensor

The large surface-to-volume ratio and highly reactive surfaces, combined with solution-processability make colloidal quantum dots (CQDs) promising to be the next generation of gas-sensing materials. However, the sizeengineering gas-sensing behavior of CQDs has not been further studied. Herein, we report the controllable synthesis of PbS CQDs with diameter sizes ranging from 2.7-7.0 nm through adjusting the injection temperature, precursor concentration and cooling rate. The results showed that the method of cold bath cooling exposed more {100} facets and enhanced NO2-sensing properties at room temperature. According to the first principle calculation, the {100} facets of PbS CQDs favors the competitive adsorption of NO2 with O2 molecules, which is in contrast with the {111} facets. At the same time, rapid cooling rate helps to increase the density of intra-band trap states of PbS CQDs, which may favor the interdot carrier hopping so as to transduce the charge transfer during the competitive adsorption between NO2 and O2 molecules into enhanced electrical current. This work reveals the microstructural mechanism underlying the size engineering of CQDs-based gas sensors.

Ultralow Detection Limit and Robust Hard X-ray Imaging Detector Based on Inch-Sized Lead-Free Perovskite Cs3Bi2Br9 Single Crystals.

Halide perovskites are promising candidates for soft X-ray detection (<80 keV) owing to their high X-ray absorption coefficient, resistivity, and mobility lifetime product. However, the lack of large high-quality single crystals (SCs) renders it challenging to manufacture robust hard X-ray imaging systems (>100 keV) with a low detection limit and stable dark current. Herein, high-quality inch-size two-dimensional (2D) Cs3Bi2Br9 (CBB) single crystals are grown from a melt via the Bridgman method. The crystal quality is enhanced by eliminating inclusions of CsBr-rich phases and restraining the trap-state density, leading to an enhanced resistivity of 1.41 × 1012 Ω cm and a mobility lifetime product of 8.32 × 10-4 cm2 V-1. The Au/CBB/Au single-crystal device exhibits a high sensitivity of 1705 μC Gyair-1 cm-2 in all-inorganic bismuth-based perovskites and an ultralow detection limit of 0.58 nGyair s-1 in all of the bismuth-based perovskites for 120 keV hard X-ray detection. The CBB detector exhibits high work stability with an ultralow dark current drift of 2.8 × 10-10 nA cm-1 s-1 V-1 and long-term air environment reliability under a high electric field of 10 000 V cm-1 owing to the ultrahigh ionic activation energy of the 2D structure. The proposed robust imaging system based on CBB SC is a promising tool for X-ray medical imaging and diagnostics.

Charge transport in SiCN/Si heterostructures

The steady-state space-charge limited (SCL) current was investigated in amorphous silicon carbonitride (a-SiCN) films deposited on single crystal silicon substrates of p-type conductivity by plasma-enhanced chemical vapor deposition (PECVD) technique. The influence of the deposition time and thermal annealing on the mechanism of the SCL current is studied. It is shown that the SCL current can be limited by shallow or deep traps, depending on the preparation condition. Experimental evidences are obtained that the traps in the films under study are associated with dangling bond defects, presumably due to the decomposition of Si–H bonds. Band and trap parameters (mobility of electrons, density and energy of trap states) are estimated from the SCL current measurements.

Synergistic Approach toward Erbium-Passivated Triple-Anion Organic-Free Perovskite Solar Cells with Excellent Performance for Agrivoltaics Application.

All-inorganic perovskite solar cells (IPSCs) have gained massive attention due to their less instability against common degradation factors (light, heat, and moisture) than their organic–inorganic hybrid counterparts. Inorganic perovskites bear a general formula of CsPbX3 (X = Cl, I, Br). The mixed halide CsPbIBr2 perovskite possesses an intermediate band gap of 2.03 eV with enhanced stability, which is still available for photovoltaic applications and the research focus of this work. We present a synergistic approach of pre-heated solution dropping with inorganic additive inclusion to deposit the organic-free triple anion CsPbIBr2 PSC. Erbium (Er)-passivated triple-anion CsI(PbBr2)0.97(ErCl3)0.03 IPSCs with inorganic carrier selective layers (CTLs), that is, organic-free, are fabricated with enhanced carrier diffusion length and crystalline grain size while lessening the grain boundaries near perovskite active layer (PAL)-bulk/carrier selective interfaces. As a result, the trap-state densities within the perovskite bulk were suppressed with stabilized CTL/PAL interfaces for smooth and enhanced carrier transportation. Therefore, for the first time, we contradict the common belief of VOC loss due to halide segregation, as a nice VOC of about 1.34 V is achieved for an organic-free IPSC through enriching initial radiative efficiency, even when halide segregation is present. The optimized organic-free IPSC yielded a power conversion efficiency of 11.61% and a stabilized power output of 10.72%, which provides the potential opportunity to integrate into agrivoltaics (AgV) projects.

Perovskite Nanocomposite Layers Engineering for Efficient and Stable Solar Cells

Recently, perovskite nanocomposites have attracted much ‎attention as active layers due to the relatively high stable efficiency of solar cells based on them. In this ‎paper, we study perovskite nanocomposite layers based on ‎semiconductive/nonconductive molecules or polymers, their deposition methods, properties, and ‎influence on the device performance. We have found that the quality of the ‎perovskite layer (morphology and crystallinity, cross-linked grains, trap states density, as well as ‎conductivity and charge carrier mobility) is strongly affected by various factors ‎related to the additive: such as type (i. e. semiconductive or nonconductive, ‎molecule or polymer), chemical structure (backbone length and ‎molecular weight, functional groups, π system, side chains, donating atoms and basicity), amount,‎ solubility, conductivity, photoactivity, polarity, hydrophobicity, and addition methods. Due to the small amounts added, these additives can lead to slight changes in energy levels, bandgap (Eg), and light absorption ‎properties. Ultimately, using the suitable deposition method and additive at an optimal amount can ‎greatly improve the stability and efficiency of the devices and reduce ‎hysteresis.

Efficient Pure Blue Light-Emitting Diodes Based on CsPbBr3 Quantum-Confined Nanoplates

Exploitation of next-generation blue light-emitting diodes (LEDs) is the foundation of the revolution in lighting and display devices. Development of high-performance blue perovskite LEDs is still challenging. Herein, 4-aminobenzenesulfonic acid (SA) is introduced to passivate blue CsPbBr3 nanoplates (NPLs), reducing the ionic migration via a more stable Pb2+-SO3-- formation, and the trap state density of films shows a 50% reduction. The inevitable Br- vacancy defects after the multistep washing process can be suppressed by a suitable MABr treatment, which can boost the external quantum efficiency (EQE) performance. It should be noted that the coverage of NPL films is another key factor to realize reproducible pure blue electroluminescence (EL). Therefore, we proposed an alternate droplet/spin coating method to improve the coverage and thickness of NPL layer to prevent hole transport layer emission and increase the reproducibility of LED performance and spectra. Furthermore, we designed hole transport layers to decrease the hole transport barrier and improve the energy-level alignment. According to SA passivation, MABr treatment, alternate droplet/spin coating method, and device structure optimization, a CsPbBr3 NPL-based pure blue (0.138, 0.046) LED with 3.18% maximum EQE can be achieved, and the half-lifetime of EL can be enhanced 1.71 times as compared to that of the counterpart LED without SA. Both performance and stability of pure blue NPL LEDs can be greatly improved via ligand passivation, alternate droplet/spin coating method, and device structure optimization, which is a trend to promote the development of pure blue perovskite LEDs in future.

Highly Efficient and Stable CsPbTh3 (Th = I, Br, Cl) Perovskite Solar Cells by Combinational Passivation Strategy.

The distorted lead iodide octahedra of all‐inorganic perovskite based on triple halide‐mixed CsPb(I2.85Br0.149Cl0.001) framework have made a tremendous breakthrough in its black phase stability and photovoltaic efficiency. However, their performance still suffers from severe ion migration, trap‐induced nonradiative recombination, and black phase instability due to lower tolerance factor and high total energy. Here, a combinational passivation strategy to suppress ion migration and reduce traps both on the surface and in the bulk of the CsPhTh3 perovskite film is developed, resulting in improved power conversion efficiency (PCE) to as high as 19.37%. The involvement of guanidinium (GA) into the CsPhTh3 perovskite bulk film and glycocyamine (GCA) passivation on the perovskite surface and grain boundary synergistically enlarge the tolerance factor and suppress the trap state density. In addition, the acetate anion as a nucleating agent significantly improves the thermodynamic stability of GA‐doped CsPbTh3 film through the slight distortion of PbI6 octahedra. The decreased nonradiative recombination loss translates to a high fill factor of 82.1% and open‐circuit voltage (V OC) of 1.17 V. Furthermore, bare CsPbTh3 perovskite solar cells without any encapsulation retain 80% of its initial PCE value after being stored for one month under ambient conditions.

Pursuing High‐Performance Organic Field‐Effect Transistors through Organic Salt Doping

AbstractDoping is an effective strategy for controlling the charge density and device performance of thin‐film electronics. Herein, a new doping system is reported for organic electronics using the organic salt p‐dopant N,N‐dimethylanilinium tetrakis(pentafluorophenyl)borate (DTB) to significantly improve the device performance of indacenodithiophene‐co‐benzothia‐diazole (IDT‐BT) organic field‐effect transistors (OFETs). With optimized doping ratios, the hole mobility increases almost fourfold from 0.32 to 1.15 cm2 V–1 s–1 and the threshold voltage reduces from −38 to 0 V. Moreover, systematical electrical characterizations demonstrate that the contact resistance and activation energy dramatically reduce in the doped devices. Such reductions are ascribed to the shift of the Fermi energy level closer to the transport level and the lowered density of trap states in doped semiconductors, as revealed by ultraviolet photoelectron spectroscopy and low‐frequency noise measurements, respectively. This study also demonstrates that the trap density increases when the doping ratio is high, explaining the device performance degradation at high doping ratios. This is the first time that DTB organic salt is used as an efficient dopant to improve the performance of OFETs, demonstrating a promising route for employing organic salt dopants to achieve high‐performance OFETs.

Negative Differential Resistance Behavior in n‐Channel Organic Thin‐Film Transistors Based on C60and PTCDI‐C8: Electrical Characterization and Parameter Extraction

Organic thin‐film transistors (OTFTs), based on two n‐type structures of fullerene (C60) andN,N′‐dioctyl‐3,4,9,10‐perylenedicarboximide (PTCDI‐C8), are investigated. The two OTFT devices reveal a negative differential resistance (NDR) behavior in the saturation region of the output curves. The OTFT based on C60shows a more pronounced NDR than that based on PTCDI‐C8. The main origin of the NDR is ascribed to the trapping states. In addition, the contact resistance (Rc) of the two devices, extracted using the developed voltage transition method (Vtrmethod), as well as the obtained values ofRc, are in fair agreement with the experimental values extracted using the total resistance. The device based on C60exhibits a higherRcthan that based on PTCDI‐C8. OTFT parameters, such as transconductance (gm), mobility (μmax), threshold voltage (Vth,), turn‐on voltage (Von), ratio currentIon/Ioff, and subthreshold slope (SS), are obtained in the linear and saturation regimes. The extracted value of SS for the OTFT based on C60is very small compared with that of the device based on PTCDI‐C8, which indicates an increase in the density of trapping states in the C60film.

Bulky ammonium iodide and in-situ formed 2D Ruddlesden-Popper layer enhances the stability and efficiency of perovskite solar cells

The practical applications of perovskite solar cells (PSCs) are limited by the further improvement of their stability and performance. Interface engineering is a promising strategy to solve these pain points. Herein, we design (R)-(-)-1-cyclohexylethylamine iodide (R-CEAI), composed of positively charged hydrophobic R-CEA+ and negatively charged I–, to post-treat the interface of 3D mixed-cation/halide perovskite with assist one of isopropyl alcohol (IPA). R-CEAI treatment not only passivates the defects at surface and grain boundaries of perovskite, but also in-situ grows quasi 2D Ruddlesden-Popper perovskite at the interface between 3D perovskite and hole transport layer, which reduces trap density of states, tunes energy level and alleviates lattice distortion. As a result, R-CEAI treated 2D/3D PSCs yield a champion PCE of 22.52%, with an improved open-circuit voltage of 1.195 V and retain 84.34% of their initial efficiency in long-term stability test, while the pristine device provides a PCE of 19.43% with only 54.30% retention.

Enhanced proton irradiation resistance in Cs-doped CH3NH3PbI3 films and solar cells

Mixed-cation perovskite solar cells have attracted tremendous attention in space applications due to their excellent power conversion efficiency (PCE) and stability to light and heat. Although the evolution of photovoltaic performance in different space environments has been investigated, the role of inorganic cesium ions (Cs+) in the enhancement of irradiation resistance needs to be further clarified. Herein, the structure and performance evolution of Cs-doped CH3NH3PbI3 (MAPbI3) films and planar heterojunction devices under proton irradiation up to 1 × 1016 p cm−2 were studied. 5% of Cs+ doping can increase the cohesive energy of MAPbI3 and effectively alleviate the lattice strain induced by proton irradiation, thereby enhancing the crystallinity and stability of films. The bandgap changes of irradiated Cs0.05MA0.95PbI3 films under the identical fluence were only one third of that of MAPbI3 films. Upon irradiation under the fluence of 1 × 1014 p cm−2, the density of trap states in the undoped and 5%Cs-doped films increased by 71% and 9%, respectively, and the average PCE of 20 corresponding devices decreased only by 12% and 9%, respectively. This proves that the replacement of organic methylamine ion with inorganic cesium ion contributes to the improvement of MAPbI3 resistance to proton irradiation, thus confirming the application prospects of mixed-cation or all-inorganic perovskite solar cells in spacecraft.

Two‐Dimensional Polycyclic Photovoltaic Molecule with Low Trap Density for High‐Performance Photocatalytic Hydrogen Evolution

Typical organic semiconductors show a high trap density of states (1016 -1018 cm-3 ), providing a large number of centers for charge-carrier recombination, thus hindering the development of photocatalytic hydrogen evolution. Here, we design and synthesize a two-dimensional polycyclic photovoltaic material, named as TPP, to reduce the trap density to as low as 2.3×1015 cm-3 , which is 1-3 orders of magnitude lower than those of typical organic semiconductors. Moreover, TPP exhibits a broad and strong absorption, ordered molecular packing with a large crystalline coherence length and enhanced electron mobility. Then, the bulk heterojunction nanoparticles (BHJ-NPs) based on a blend of polymer donor (PM6) and TPP exhibit an average hydrogen evolution rate (HER) of 64.31 mmol h-1 g-1 under AM1.5G sunlight (100 mW cm-2 ), and 72.75 mmol h-1 g-1 under 330-1100 nm illumination (198 mW cm-2 ) higher than that of the control NPs based on typical PM6 : Y6 (62.67 mmol h-1 g-1 ).

Two‐Dimensional Polycyclic Photovoltaic Molecule with Low Trap Density for High‐Performance Photocatalytic Hydrogen Evolution

AbstractTypical organic semiconductors show a high trap density of states (1016–1018 cm−3), providing a large number of centers for charge‐carrier recombination, thus hindering the development of photocatalytic hydrogen evolution. Here, we design and synthesize a two‐dimensional polycyclic photovoltaic material, named as TPP, to reduce the trap density to as low as 2.3×1015 cm−3, which is 1–3 orders of magnitude lower than those of typical organic semiconductors. Moreover, TPP exhibits a broad and strong absorption, ordered molecular packing with a large crystalline coherence length and enhanced electron mobility. Then, the bulk heterojunction nanoparticles (BHJ‐NPs) based on a blend of polymer donor (PM6) and TPP exhibit an average hydrogen evolution rate (HER) of 64.31 mmol h−1 g−1under AM1.5G sunlight (100 mW cm−2), and 72.75 mmol h−1 g−1under 330–1100 nm illumination (198 mW cm−2) higher than that of the control NPs based on typical PM6 : Y6 (62.67 mmol h−1 g−1).

Interlayer Modification Using Phenylethylamine Tetrafluoroborate for Highly Effective Perovskite Solar Cells

Although the best research-cell efficiency of perovskite solar cells (PSCs) has exceeded 25%, the industrial application of PSCs is limited by further improvement of performance and stability. Interface engineering is a prospective method to overcome these issues. Here, phenylethylamine tetrafluoroborate (PEABF4) is introduced into the interlayer between the TiO2 electron transport layer (ETL) and the perovskite layer. The introduction of PEABF4 effectively passivates the oxygen vacancy via coordination of BF4– with Ti and mitigates inherent trap-state density and nonradiative recombination in the devices. Moreover, the modification of PEABF4 optimizes the energy match between the perovskite layer and the TiO2 ETL and improves the crystal quality of the perovskite. Consequently, the PEABF4-modified PSCs achieve a power conversion efficiency of 21.21%, accompanied with excellent environmental stability, while the pristine device exhibits an efficiency of 19.25%.

Silk fibroin induced homeotropic alignment of perovskite crystals toward high efficiency and stability

The photoactive lead halide perovskites with a highly crystalline structure and low trap state density were regarded as the prerequisites for achieving high photovoltaic performance. The perovskite thin films were typically synthesized by simple wet chemistry routes, where the fluctuations in the fabrication readily generate lattice defects and induce stacking faults during the crystal growth. The growth of highly crystalline and low-defect perovskite usually needs complicated synthetical manipulation and well-designed additive engineering. Here in this work, we reported a naturally available protein, silk fibroin (SF), whereby the highly ordered β-sheets component can adequately interact with perovskite intermediates and work as the crystal growth template and trap passivation agent, which induced facile self-assembly of the perovskite crystals with homeotropic alignment structure and low defect concentrations. As a result, the SF incorporated perovskite layer exhibited a much-improved conversion efficiency with charge carrier mobility 1000 times higher than that of pristine film, as well as showed robust stability under various harsh conditions.

The Influence of CsBr on Crystal Orientation and Optoelectronic Properties of MAPbI3-Based Solar Cells.

Crystal orientations are closely related to the behavior of photogenerated charge carriers and are vital for controlling the optoelectronic properties of perovskite solar cells. Herein, we propose a facile approach to reveal the effect of lattice plane orientation distribution on the charge carrier kinetics via constructing CsBr-doped mixed cation perovskite phases. With grazing-incidence wide-angle X-ray scattering measurements, we investigate the crystallographic properties of mixed perovskite films at the microscopic scale and reveal the effect of the extrinsic CsBr doping on the stacking behavior of the lattice planes. Combined with transient photocurrent, transient photovoltage, and space-charge-limited current measurements, the transport dynamics and recombination of the photogenerated charge carriers are characterized. It is demonstrated that CsBr compositional engineering can significantly affect the perovskite crystal structure in terms of the orientation distribution of crystal planes and passivation of trap-state densities, as well as simultaneously facilitate the photogenerated charge carrier transport across the absorber and its interfaces. This strategy provides unique insight into the underlying relationship between the stacking pattern of crystal planes, photogenerated charge carrier transport, and optoelectronic properties of solar cells.

Study on H plasma treatment enhanced p-GaN gate AlGaN/GaN HEMT with block layer

&lt;sec&gt;High electron mobility transistors(HEMTs)show tremendous potentials for high mobility, high breakdown voltage, low conduction, low power consumption, and occupy an important piece of the microelectronics field. The high-resistivity-cap-layer high electron mobility transistor (HRCL-HEMT) is a novel device structure. Based on the hole compensation mechanism, the p-GaN is converted into high resistance semiconductor material by hydrogen plasma implantation. Thus, the surface of the p-GaN layer will have a serious bombardment damage under the hydrogen plasma implantation. In practical work, it is also very challenging in the accurate controlling of the hydrogen injection rate, injection depth and injection uniformity. To achieve the required depth of injection, the injected hydrogen plasma is often more than the required dose or multiple injections times. The energy of hydrogen plasma plays a huge influence on the surface of the p-GaN layer.The leakage current will be generated on the device surface, which deteriorates the electrical performance of the device.&lt;/sec&gt;&lt;sec&gt;In this work, to protect the surface of p-GaN layer, a 2-nm Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film is deposited on the surface of the p-GaN cap layer to reduce the implantation damage caused by hydrogen plasma treatment. The research shows that after the device deposited Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film prior to the hydrogen plasma treatment, the gate reverse leakage current is reduced by an order of magnitude, the ratio of &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;ON&lt;/sub&gt; to &lt;i&gt;I&lt;/i&gt;&lt;sub&gt;OFF&lt;/sub&gt; is increased by about 3 times. Meanwhile, the OFF-state breakdown voltage is increased from 410 V to 780 V. In addition, when the bias voltage is 400 V, the values of dynamic &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;ON&lt;/sub&gt; of devices A and B are 1.49 and 1.45 respectively, the device B shows a more stable dynamic performance. To analyze the gate leakage mechanism, a temperature-dependent current&lt;i&gt; I&lt;/i&gt;&lt;sub&gt;G&lt;/sub&gt;-&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;G&lt;/sub&gt; testing is carried out, and it is found that the dominant mechanism of gate leakage current is two-dimensional variable range hopping (2D-VRH) at reverse gate voltage. The reason for reducing the gate reverse current is analyzed, and the Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film increases the activation energy of trap level and changes the surface states of HR-GaN; furthermore, the Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film blocks the injection of too much H plasma, thereby reducing the density of AlGaN barrier and channel trap states, and weakening the current collapse.&lt;/sec&gt;

High-Performance a-IGZO TFT Fabricated With Ultralow Thermal Budget via Microwave Annealing

In this work, we report high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with atomic layer deposited Al₂O₃ dielectric processed at a minimal temperature of 189.6 &#x00B0;C via microwave annealing (MWA). The a-IGZO TFT with MWA exhibits an improvement of 57&#x0025; in subthreshold swing (SS) compared with the unannealed device; meanwhile, it retains high field-effect mobility of up to 29.2 cm²/(V <inline-formula> <tex-math notation="LaTeX">$\cdot $ </tex-math></inline-formula> s) and large switching ratio of &#x003E;10⁸. Moreover, the SS of the device was further reduced through a two-step MWA treatment. It is believed that MWA treatment effectively reduces the density of trap states associated with oxygen vacancies, promotes the formation of lattice oxygen, and thus improves the quality of IGZO film. MWA with low thermal budget shows great potential in applications of the back-end of line (BEOL)-compatible oxide devices.

Double perovskite Cs2AgBiBr6 radiation sensor: synthesis and characterization of single crystals

Single crystals of lead-free halide double perovskite Cs2AgBiBr6 sensor material manifest a remarkable potential for application in radiation detection and imaging. In this study, the purity and crystallinity of solution-grown Cs2AgBiBr6 single crystals with cubic Fmoverline{3}m symmetry have been corroborated by powder XRD measurements, while the single crystal XRD patterns reveal the dominant {111} lattice planes parallel to the sample surfaces. A wider range of lower resistivity values (106–109 Ωcm) was obtained from the I-V measurements compared to the 1.55 × 109–6.65 × 1010 Ωcm values from the van der Pauw method, which is typically higher for the Ag than for the carbon paint electrodes. Charge-carrier mobility values estimated from the SCLC method for the carbon paint-Cs2AgBiBr6 (1.90–4.82 cm2V−1 s−1) and the Ag-Cs2AgBiBr6 (0.58–4.54 cm2V−1 s−1) including the density of trap states (109–1010 cm−3) are comparable. Similar values of 1.89 cm2V−1 s−1 and 2.36 cm2V−1 s−1 are derived from the Hall effect measurements for a sample with carbon and Ag electrodes, respectively. The key electrical parameters including the X-ray photoresponse measurements indicate that the Cs2AgBiBr6 samples synthesized in this study satisfy requirements for radiation sensors.Graphical abstract

Ternary strategy enabling high-efficiency rigid and flexible organic solar cells with reduced non-radiative voltage loss

The addition of ZY-4Cl into the host PM6:BTP-eC9 can result in reduced density of trap states and suppressed non-radiative recombination, thus enabling the ternary device with an obviously lower voltage loss than either of the binary devices.