Low Trap-state Density Research Articles

Bilayer interface engineering through 2D/3D perovskite and surface dipole for inverted perovskite solar modules

The persistency of passivation and scalable uniformity are vital issues that limit the improvement of performance and stability of large-area perovskite solar modules (PSMs). Here, we design a bilayer interface engineering strategy that takes advantage of the stability and passivation ability of low-dimensional perovskite and the dipole layer. Introducing phenethylammonium iodide (PEAI) can form 2D/3D heterojunctions on the perovskite surface and effectively passivate defects of perovskite film. Interestingly, the upper piperazinium iodide (PI) layer can still form surface dipoles on the 2D/3D perovskite surface to optimize energy-level alignment. Moreover, the bilayer interface engineering enables large-area perovskite films with uniform surface morphology, lower trap-state density and stability against environmental stress factors. The final devices achieved a small-area PCE of 25.20% and a large-area (1 cm2) PCE of 23.96%. A perovskite mini-module (5 × 5 cm2 with an active area of 14.28 cm2) could also be fabricated to achieve a PCE of 23.19%, ranking it among the highest for inverted PSMs. Additionally, the device could retain over 93% of its initial efficiency after MPP tracking at 45 °C for 1280 hours. This study successfully demonstrates a bilayer interface engineering with respective functions, offering valuable insights for producing efficient and stable large-area PSCs.

Emulating Low-Power Synaptic Plasticity in a Solution-Processed Oxide-Based Long Retention Memory Transistor with High Learning Accuracy.

The exploration of synaptic plasticity in metal-oxide-based ferroelectric thin-film transistors has been limited. As a perovskite ferroelectric material, LiNbO3 is widely studied; but its potential use as a neuromorphic device, like synaptic transistors, has not been realized. In this study, a solution-processed ferroelectric thin-film transistor (FeTFT) with an alternating layer of LiNbO3 and Li5AlO4 as a gate dielectric has been fabricated. This configuration reduces the depolarization field by leveraging the large ionic polarization of Li+ ions in the Li5AlO4 layer, while the wide bandgap helps mitigate the leakage current. FeTFT exhibits impressive transistor performance, including a saturation mobility of 0.478 cm2V-1 s-1, an on/off ratio of 3.08 × 103, and a low trap-state density of 1.3 × 1013 cm-2. Moreover, the device demonstrates good memory retention, retaining information for nearly 1 day. It successfully emulates synaptic plasticity, specifically short-term plasticity and long-term plasticity. Besides, a 94% training accuracy has been achieved through artificial neural network simulation. Notably, the FeTFT consumes minimal power, with energy consumption of approximately 3.09 nJ per synaptic event, which is remarkably low compared to other reported solution-processed FeTFT devices.

Reduced trap state density in AlGaN/GaN HEMTs with low-temperature CVD-grown BN gate dielectric

In this Letter, low-temperature (400 °C) chemical vapor deposition-grown boron nitride (BN) was investigated as the gate dielectric for AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on a Si substrate. Comprehensive characterizations using x-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, atomic force microscope, high-resolution transmission electron microscopy, and time-of-flight secondary ion mass spectrometry were conducted to analyze the deposited BN dielectric. Compared with conventional Schottky-gate HEMTs, the MISHEMTs exhibited significantly enhanced performance with 3 orders of magnitude lower reverse gate leakage current, a lower off-state current of 1 × 10−7 mA/mm, a higher on/off current ratio of 108, and lower on-resistance of 5.40 Ω mm. The frequency-dependent conductance measurement was performed to analyze the BN/HEMT interface, unveiling a low interface trap state density (Dit) on the order of 5 × 1011–6 × 1011 cm−2 eV−1. This work shows the effectiveness of low-temperature BN dielectrics and their potential for advancing GaN MISHEMTs toward high-performance power and RF electronics applications.

Energy Transfer-Dominated Quasi-2D Blue Perovskite Light-Emitting Diodes.

The bromide-chloride mixed quasi-two-dimensional (2D) perovskite, with a natural quantum well structure and tunable exciton binding energy, has gained significant attention for high-performance blue perovskite light-emitting diodes (PeLEDs). However, the relative importance of having a low trap state density or efficient exciton transfer for high-efficiency electroluminescence (EL) performance remains elusive. Here, two molecules with the benzoic acid group, sodium 4-fluorobenzoate (SFB) and 3,5-dibromobenzoic acid (DBA), are used to modulate the phase distribution and trap state to explore the effect between energy transfer and defect passivation. As a result, when the n = 1 phase is inhibited in both films, the DBA@SFB-modified perovskite films achieve a higher photoluminescence quantum yield (PLQY) than the SFB-modified perovskite films due to effective defect passivation. However, DBA@SFB-modified PeLEDs exhibit lower external quantum efficiency (EQE) compared to SFB-modified PeLEDs due to the poor exciton transfer between the low-dimensional phase. This demonstrates that passivation strategies may enhance photoluminescence through reducing nonradiative recombination, but the effect of phase distribution is pivotal for EL performance by efficient energy transfer in quasi-2D perovskites. Femtosecond time-resolved transient absorption measurements confirm the fastest carrier dynamics in SFB-modified perovskite films, further corroborating the above result. This work provides useful information about phase modulation and defect passivation for high-efficiency blue quasi-2D PeLEDs.

Influence of highly optimized charge carrier mobility and diverse physical features toward efficient organic solar cells

Organic solar cells (OSCs) exhibit potential in low-emissive photovoltaic (PV) technology by enhancing excitonic absorption, higher trap-assist recombination, lower excitons diffusion length (Ln,p), and carrier lifetime (τ n,p). The main challenge remains the asymmetric carrier mobility (μ n,p) of the organic absorbing layer (OAL) and various physical factors affecting efficiency (η). This effort has been explored through the attributes of different fullerene derivatives based on binary blends of OAL thickness that suggest new physical insights into the roles of several contributions in the PV performances under intense light illumination. The relationship between optimum mobility ratio (β) and lower trap-state density (Nt) of OAL in OSC structures for inclusive η has been collectively investigated. With a very thin OAL and pioneering transparent hole transport layers (HTLs) can significantly reduce recombination loss and enhance transparency, focusing on near-infrared band absorption and thin hetero-interface design for η and stability. The improved thin OALs, tunable absorption bands, and carrier selectivity address efficiency–transparency trade-offs and reproducibility concerns. The outcome revealed a stable η of 6.27% with a 250 nm thinnest OAL at a temperature of 300 K, which may be interpreted as a coupled framework for effective optimization strategies to accomplish balance between photogeneration and charge carrier recombination. Thus, the observed hypothetically analyzed results have verified the further optimization of OAL thickness for fabrication perspectives with a typical interpretation of ohmic contact.

Revealing the stability origins of 596 days-humidity-stable semitransparent perovskite solar cells

Hybrid organic–inorganic perovskites (HOIPs) hold promise in the field of optoelectronics due to their excellent photoelectric conversion efficiency. However, the ion migration and hygroscopicity of these perovskite solar cells need to be addressed. Here, we presented semitransparent perovskite solar cells (ST-PSCs) using hole transport layer (HTL) combined with polyaniline (PANI) to stabilize HTL/perovskite interface, achieving a humidity durability (RH, 50%–90%) for 596 days (14304 h) without encapsulation. Moreover, the decrease in hydrolysis products (LiF) showed the interaction between PANI with the additives in HTL dramatically inhibited the water uptake and corrosion on MAPbI3 layer. The PANI modified samples had a higher I/Pb ratio and lower trap state density, which indicated the passivation effect of PANI on the uncoordinated Pb2+ and iodine vacancies. Subsequently, PANI successfully stabilized the interface and perovskite by inhibiting the formation of Pb0 and Au migration as long period storage. This work presented an interfacial design to develop HOIP in air with high humidity stability.

Emerging lead-free all inorganic perovskite single crystals K7Bi3X16 (X = Cl, Br) toward photodetector application.

Lead-free inorganic perovskites have attracted intensive attention in the field of photodetectors owing to their high stability, non-toxicity, and remarkable photoelectric characteristics. Herein, we designed and developed a series of thus-far unreported lead-free all inorganic perovskite single crystals, K7Bi3X16 (X = Cl, Br). In particular, we resorted to cooling crystallization and intercalated K+ to inorganic Bi-Br and Bi-Cl frameworks as inorganic A-site cations, obtaining zero-dimensional (0D) K7Bi3X16 (X = Cl, Br) perovskite single crystals, which display suitable bandgaps, excellent electron mobility and low trap-state density, as analysed by experimental characterization and density functional theory (DFT) calculations. Accordingly, the vertical structure K7Bi3Br16 photodetector can achieve a fast ON/OFF switch under the irradiation of 395 nm light. When the light intensity is 5 mW cm-2 and the voltage is 3 V, the responsivity is calculated to be 0.052 mA W-1. The above characteristics make K7Bi3Br16 a promising material for fabricating ultraviolet photodetectors.

Intermediate Phase Free α-FAPbI3 Perovskite via Green Solvent Assisted Perovskite Single Crystal Redissolution Strategy.

Perovskite single-crystal redissolution (PSCR) strategy is highly desired for efficient formamidinium lead triiodide (FAPbI3 ) perovskite photovoltaics with enhanced phase purity, improved film quality, low trap-state density, and good stability. However, the phase transition and crystallization dynamics of FAPbI3 remain unclear in the PSCR process compared to the conventional fabrication from the mixing of precursor materials. In this work, a green-solvent-assisted (GSA) method is employed to synthesize centimeter-sized α-FAPbI3 single crystals, which serve as the high-purity precursor to fabricate perovskite films. The α-FAPbI3 PSCR strategy facilitates direct α-phase formation and inhibits the complex intermediate phases monitored by in situ grazing-incidence wide-angle X-ray scattering. Moreover, the α-phase stability is prolonged due to the relaxation of the residual lattice strain through the isotropic orientation phase growth. Consequently, the GSA-assisted PSCR strategy effectively promotes crystallization and suppresses non-radiative recombination in perovskite solar cells, which boosts the device efficiency from 22.08% to 23.92% with significantly enhanced open circuit voltage. These findings provide deeper insight into the PSCR process in terms of its efficacy in phase formation and lattice strain release. The green low-cost solvent may also offer a new and ideal solvent candidate for large-scale production of perovskite photovoltaics.

Room-temperature growth of perovskite single crystals via antisolvent-assisted confinement for high-performance electroluminescent devices

Organic-inorganic halide perovskite single crystals (OIHP-SCs) are promising light-emitting materials for bright electroluminescence (EL) devices due to their superior optoelectronic properties and excellent stability. However, the conventional high-temperature growth methods will inevitably disturb the ordered growth and introduce massive defects in OIHP-SCs, leading to the degradation of device performance. The preparation of thin OIHP-SCs with low trap-state densities for high-performance EL devices remains a formidable challenge. Here, we develop an efficient antisolvent-assisted confined growth (AACG) method for the room-temperature growth of formamidinium lead bromide (FAPbBr3) perovskite SCs. An antisolvent vapour environment is intentionally introduced in the spatially confined growth process to lower the free energy barrier for nucleation, enabling the growth of high-quality FAPbBr3 SCs at room temperature. Consequently, FAPbBr3 SCs with ultralow trap-state density of 2.15 × 109 cm−3 and amplified spontaneous emission (ASE) threshold of 7.1 µJ cm−2 could be achieved, representing the best results ever reported for FAPbBr3 SCs. By leveraging the high crystal quality of FAPbBr3 SCs, SC-based perovskite light-emitting diodes (PeLEDs) with a high luminance of over 26,000 cd m−2 and a peak current efficiency (CE) of 13.02 cd A−1 are demonstrated. Our work opens up new opportunities for the development of high-performance EL devices based on OIHP-SCs.

A facile strategy for highly efficient perovskite crystals fabricated in a high moisture environment via solvent engineering process

BackgroundHybrid organic perovskite solar cells (PSCs) have recently gained recognition for their excellent photovoltaic properties. However, most PSCs were fabricated in a nitrogen-filled glovebox to prevent damage from moisture. Overcoming humidity damage is crucial for PSC fabrication in an ambient atmosphere. Fabricating perovskite solar cells (PSCs) under ambient atmosphere conditions needs the aid of substrate heating or air-knife flow to rapidly evaporate solvents. MethodsHerein, we propose a facile solvent engineering method without extra equipment or processes for fabricating highly efficient PSCs in a high moisture condition by a one-step spin-coating process. Acetone incorporation into the perovskite precursor solution not only prevents the ingress of moisture, but also accelerates the volatilization of solvents during the crystallization process. Significant findingsThe as-prepared PSCs feature low trap-state density, high charge recombination resistance, low hysteresis, and long charge lifetime. Little MABr and PbBr2 are separated out to passivate interface/grain-boundary defects. At a 10% acetone incorporation, the highest power conversion efficiency can reach 17.75% for the PSC fabricated in 70% relative humidity. The work provides a facile, promising method to prepare highly efficient PSCs in an ambient atmosphere.

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.

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.

High-performance layer-structured Si/Ga2O3/CH3NH3PbI3 heterojunction photodetector based on a Ga2O3 buffer interlayer.

Organic-inorganic metal halide perovskite-based photodetectors (PDs) have attracted great attention because they exhibit extraordinary optoelectronic performances due to advantages such as a low trap-state density and large absorption coefficient. As a buffer layer, G a 2 O 3 can block electron hole recombination, passivate an Si surface, reduce trap density, and improve the ability of electron tunneling. Here, we demonstrate a trilayer hybrid structure (S i/G a 2 O 3/C H 3 N H 3 P b I 3) composed of an n-type silicon wafer, G a 2 O 3 interlayer, and C H 3 N H 3 P b I 3 thin film. The effect of different G a 2 O 3 layer thicknesses on the characteristics of a PD was studied, which shows that the responsivity first increases and then decreases with an increase in the G a 2 O 3 film thickness; the optimized G a 2 O 3 thickness is 300nm. Additionally, the optimal responsivity, detectivity, and the rise and decay times are 7.2m A W -1, 7.448×1010 Jones, and 39 and 1.7ms, respectively. This device has a better performance because G a 2 O 3 and perovskite have a matched energy level. We believe our work could provide a new way to fabricate high-performance optoelectronic devices.

Improvement of electrical properties of ZnO TFT with NbLaO-based stacked gate dielectrics

The double-stacked gate dielectrics (DSGD), which consisted of either NbLaO/Al2O3 or NbLaO/SiO2, were used to improve the electrical performance of zinc oxide thin-film transistor (ZnO-TFT) with single-layer NbLaO gate dielectric (SLGD). Compared to ZnO-TFT with SLGD, the ZnO-TFTs with DSGD exhibit better electrical performance, specifically for the device with the NbLaO/SiO2 DSGD, with an increase of the field-effect mobility from 5.77 cm2V[Formula: see text]s[Formula: see text] to 39.64 cm2V[Formula: see text]s[Formula: see text], an enhancement of the on/off current ratio by two orders of magnitude, a reduction of the subthreshold slope from 110 mV/decade to 70 mV/decade. The performance enhancements are attributed to a low root-mean-square surface roughness of less than 0.3 nm and a low trap-state density of less than [Formula: see text] cm[Formula: see text] (even [Formula: see text] cm[Formula: see text] for the NbLaO/SiO2 DSGD) in the bulk of the channel and at the ZnO/NbLaO interface. The results imply that ZnO-TFTs with DSGD have the potential for the application of high-resolution flat panel display.

Enhancing the Performance of Perovskite Solar Cells by 4‐Chloro‐1,8‐Naphthalic Anhydride for Surface Passivation

AbstractOn the surface and grain boundary of perovskite films there are large quantities defects, which leads to photogenerated carrier nonradiative recombination and degrades the performance of the perovskite solar cells (PSCs). Surface passivation can suppress the detrimental effects of defect and improve the performance of PSCs. Here, an organic molecule, 4‐chloro‐1,8‐naphthalic anhydride (ALS), is adopted to passivate the defects on the surface and grain boundary of (FAPbI3)0.95(MAPbBr3)0.05 perovskite films. The oxygen of carbonyl group in the ALS provides lone pair electron to the undercoordinated Pb2+ and passivated this defect. The ALS passivated perovskite films have lower trap state density and longer carrier lifetime. As a result, the photoelectric conversion efficiency (PCE) of the PSCs was improved from 21.52% to 23.72%. Furthermore, the ALS passivated PSC show good stability, and it could maintain 88% of its initial efficiency after 1200 h storage in ambient atmosphere without encapsulation.

Anionic surfactant anchoring enables 23.4% efficient and stable perovskite solar cells

Nonradiative recombination losses at defects in metal halide perovskite films are responsible for hindering the improvement of the photovoltaic performance and stability of perovskite solar cells (PSCs). Here, we report a feasible multifunctional additive strategy that uses cesium stearate to passivate defects in perovskite films and simultaneously enhances the tolerance to light and moisture stress. Nonradiative recombination losses are effectively suppressed in target films that exhibit improved crystallinity, low trap-state density, and enhanced carrier separation and transportation. The present strategy hence boosts the power conversion efficiency of the p-i-n structured PSC to 23.41%. Our device also shows good stability in ambient air without encapsulation, maintaining 91.6% of the initial efficiency after 720 h.

Synergistic effect of dual anions for efficient and stable quasi 2D perovskite solar cell

Quasi two-dimensional perovskite solar cells (Q-2D PSCs) has attracted the attention of many researchers in recent years due to improved stability compared to their three-dimensional (3D) counterparts. However, the insulation of organic cation could hinder charge transfer between the octahedral sheets, thereby decreasing photoelectric performance of Q-2D PSCs. Here, the study of the synergistic effect of MACl and GuSCN on crystal orientation and quality of films based on the 4F‐PEA 2 MA 4 Pb 5 I 16 perovskite are reported. The Q-2D perovskite film exhibits more vertical orientation growth and lower trap-state density with the effect of dual additive. As a result, the device obtained a power conversion efficiency (PCE) of 15.05% for planar p-i-n solar cell using the Q-2D perovskite film with dual additive, which retained an average of 85% of their initial PCEs after 300 h in an ambient environment with humidity of 50 ± 10%. This result indicates that the use of dual additive MACl and GuSCN is an effective way to adjust the crystal orientation and quality of perovskite films, which are key factors to influence the performance of Q-2D PSCs. • The Q-2D perovskite film 4F‐PEA 2 MA 4 Pb 5 I 16 with dual additives (MACl and GaSCN) was prepared for the first time. • With the synergistic effect, the high-quality Q-2D perovskite film with more vertical orientation was obtained. • There was a larger concentration window of GaSCN additive in the presence of MACl due to their synergistic effect. • Compared with the Q-2D PSCs without additive, the PCE of Q-2D PSCs based on dual additives increased by 1.76 times.

Heterojunction In Situ Constructed by a Novel Amino Acid-Based Organic Spacer for Efficient and Stable Perovskite Solar Cells.

The optical properties and stability of metal halide perovskites can be improved by reducing their dimensionality. Because defects at the perovskite film grain body and boundaries cause significant energetic losses by nonradiative recombination, perovskite films with manageable crystal size and macroscopic grains are essential to improve the photovoltaic properties. Through theoretical calculation models and experiments, we show that the carboxyl group of 4-ammonium butyric acid-based cation (4-ABA+) can interact with the three-dimensional (3D) perovskite to produce in situ a secondary grain growth by post-treatment. It passivates the trap defects and broadens the light absorption. 4-ABA+ could induce a 2D capping layer on top of 3D mixed cation-based perovskite to construct a 2D/3D heterojunction. The 4-ABA+-modified perovskite film consists of large-sized grains with extremely low trap state densities and possesses a longer charge carrier lifetime and good stability, resulting in efficient perovskite solar cells with a champion efficiency of 23.16% and a VOC of 1.20 V. We show that the 4-ABA+-treated devices outperform the 3-ammonium propionic acid (3-APA+)- and 5-ammonium valeric acid (5-AVA+)-treated ones. Moreover, the devices exhibit high stability under high humidity and continuous light soaking conditions. This work gives a hint that our approach based on 4-ABA+ treatment is key to achieving better electrical properties, a controlled crystal growth, and highly stable perovskite solar cells.

Ultrathin single-crystalline perovskites: Toward large area wafers

The growth of large-area ultrathin single-crystalline wafers of methylammonium lead bromide is investigated on a hole transport layer using a diffusion-facilitated inverse temperature crystallization method. It is shown that, in addition to the hydrophobic confining layers, optimized precursor molar ratio and growth temperature are essential for realizing large-area single-crystalline wafers of device-friendly thickness in the range of 20–30 µm. The necessity of the hydrophobic layer for the realization of large-area wafers using the space confined crystal growth method is explained from consideration of the occurrence of heterogeneous nucleation. Space-charge limited current studies of the device fabricated with the synthesized single-crystal wafer show excellent charge transport mobility of 2.12 cm2/vs and a low trap-state density of 1.34 ⋅ 1011 cm−3.

Maltose as an Ecofriendly Modifier of the Buried Interface for Efficient and Stable Inverted Perovskite Solar Cells

A new concept of modifying the buried interface with ecofriendly material to improve the photovoltaic performance of inverted perovskite solar cells (PSCs) is proposed. A low‐cost and ecofriendly maltose with multihydroxyl groups is facilely chosen for the proof of our concept. The maltose modification not only improves the hole mobility of hole transporting layer, but also regulates the formation of a high‐quality perovskite film with a low density of gain boundary and trap states. The resulting inverted PSCs show a champion power conversion efficiency of 20.65% with negligible hysteresis, accompanied by enhanced thermal and operational stability. This work shows that buried interface engineering with ecofriendly materials opens a new avenue to further improve the efficiency and stability of sustainable PSCs.