Organolead Trihalide Perovskite Research Articles

Solution-grown BiI/BiI3 van der Waals heterostructures for sensitive X-ray detection

X-ray detectors must be operated at minimal doses to reduce radiation health risks during X-ray security examination or medical inspection, therefore requiring high sensitivity and low detection limits. Although organolead trihalide perovskites have rapidly emerged as promising candidates for X-ray detection due to their low cost and remarkable performance, these materials threaten the safety of the human body and environment due to the presence of lead. Here we present the realization of highly sensitive X-ray detectors based on an environmentally friendly solution-grown thick BiI/BiI3/BiI (BixIy) van der Waals heterostructure. The devices exhibit anisotropic X-ray detection response with a sensitivity up to 4.3 × 104 μC Gy−1 cm−2 and a detection limit as low as 34 nGy s−1. At the same time, our BixIy detectors demonstrate high environmental and hard radiation stabilities. Our work motivates the search for new van der Waals heterostructure classes to realize high-performance X-ray detectors and other optoelectronic devices without employing toxic elements.

Electrical and Optoelectrical Dual-Modulation in Perovskite-Based Vertical Field-Effect Transistors

Organolead trihalide perovskites have drawn a great deal of interest for application in electronic and optoelectronic devices owing to their exceptional physical properties. However, the majority of reported perovskite field-effect transistors (FETs) demonstrates unsatisfactory performance, such as poor mobility, low on/off ratio, and low current density, which remains a significant obstacle for their potential applications. In this work, we report a vertical FET (VFET) composed of a single-crystalline MAPbBr3 perovskite Schottky junction, which effectively modulates the intrinsic carrier characteristics and enhances the performance of the device by reducing channel length and weakening the electrostatic screening effect. The device exhibits excellent performance with a high on/off ratio (104), high carrier mobility (23.4 cm2 V–1 s–1), and current density of 2.69 A cm–2 at room temperature. Importantly, the regulation of the drain voltage plays a similar role to that of the gate voltage in our device, which is attributed to the doping of perovskite with regulation of the source contact/perovskite Schottky junction. With the drain modulation, a superior photoresponse with enhanced responsivity of 16 A W1– and a low dark current are simultaneously obtained under light illumination, leading to a high detectivity of 1014 Jones. Our research may open up new possibilities for perovskite electronics, such as logic applications for various flexible, wearable, and disposable devices.

Numerical Investigation into Photovoltaic Performance of Organolead Trihalide Perovskite Quantum Dot Intermediate Band Solar Cell

In this work, an intermediate band solar cell (IBSC) model consisting of MAPbI3 quantum dots (QD) and MAPbCl3 barrier material is explored analytically with MATLAB. Titanium di-oxide (TiO2) is used as transport layer for electron and Spiro-OMeTAD (2,2',7,7'-tet-rakis (N,N'-di-p-methoxyphenylamine)–9,9' spirobifluorene) is used as transport layer for hole. Fluorine-doped tin oxide (FTO) and Silver (Ag) is used as top and bottom contact. The impact of QD size and dot spacing on the key parameters of MAPbI3 QD-IBSC is illustrated throughout this paper. In order to identify the number of IB in a single regime, Schrödinger equation is solved as a function of host energy gap using Kronig–Penney model. The detailed balance limit assumptions with unity fill factor are applied to extract highest efficiency from the system. For any case, face centered cubic (FCC) crystal structure is assumed. The (100) crystal orientation is considered as charge carriers from n–region to p–region transport in this orientation. Major performance indicators of the device such as photocurrent intensity Jsc, open circuit voltage Voc and power conversion efficiency η have been delineated. Highest efficiency of 63% is attained for dot size of 4 nm and dot spacing of 1.5 nm.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Reduced Defects and Enhanced Performance of (FAPbI3)0.97(MAPbBr3)0.03-Based Perovskite Solar Cells by Trimesic Acid Additives.

A high-quality organolead trihalide perovskite film with large-sized crystalline grains and smooth surfaces is required to obtain efficient perovskite solar cells (PSCs). Herein, high-quality (FAPbI3)0.97(MAPbBr3)0.03 perovskite films were fabricated using trimesic acid (TMA) additives in a halide perovskite precursor solution to obtain efficient PSCs. The X-ray diffraction analysis and scanning electron microscopy of the films revealed that the TMA had a significant effect on the roughness of the films by acting as a surface link, thus reducing the surface defects and recombination at the grain boundaries. In addition, with the addition of the TMA additive, a smooth perovskite film with a flat surface and no pinholes was obtained. The perovskite film was used to fabricate a PSC device, and the device exhibited a high power conversion efficiency of 17.26%, which was higher than that of the control device (15.15%) under the same conditions. This study demonstrates a facile method to passivate defects on the perovskite layer via surface modification.

Impact of stress testing and passivation strategies on low-cost carbon-based perovskite solar cell under ambient conditions

The use of organolead trihalide perovskite material has been an important milestone in the field of photovoltaics with power conversion efficiencies reaching up to 25.6% in 2021. The light absorbing layer of the perovskite solar cell (PSC) plays a pivotal role in establishing long-term efficiency and stability. Stabilization of these perovskite phases is crucial for the efficient charge transfer dynamics, leading to a better optoelectronic performance. However, the perovskite layer may undergo undesirable phase transitions when exposed to environmental stressors. This impediment can be allayed by having a better understanding of the stress testing regimes and proper passivation strategies leading to their commercial scalability. In the present study, three types of perovskite materials are used for stress testing so as to observe the influence of atmospheric stressors on the type of perovskite materials used. An accelerated ageing test was performed on PSCs with simultaneous combination of heat and humidity. Our results show that FA-MA-Cs based mixed cationic lead halide perovskite are better suited for endurance against environmental stressors retaining almost 50% of PCE post stress test. The champion PSC samples were then subjected to two different modes of low-cost passivation techniques for perovskite absorber layer using acetic acid and CaCl2 as passivating agents. Acetic acid treated samples managed to have lower hysteresis values, lower yellow phase-based degradation and a PCE of up to 15% as compared to control samples. CaCl2 treated samples on the other hand had improved open-circuit voltage values and had more homogenous distribution with better resistance against recombined electrons.

High-Temperature Stable FAPbBr3 Single Crystals for Sensitive X-ray and Visible Light Detection toward Space.

Organolead trihalide perovskite single crystals (SCs) offer unprecedented opportunity for X-ray and visible light detection. Nevertheless, it remains a challenge to keep simultaneous high-performance and stability at a high-temperature working mode. Herein, formamidinium lead bromide (FAPbBr3) SCs are developed to successfully address these issues. Low-temperature crystallized induced FAPbBr3 SCs possess an excellent mobility-lifetime product and an ultralow surface charge recombination velocity, thus exhibiting an X-ray dose rate as low as 0.3 μGyair s-1 as a sensitive radiation detector. Furthermore, it also contributes a specific detectivity as high as 3.5 × 1012 cm Hz1/2 W-1, keeping stable at high-temperature of 460 K as a photodetector. A prototype of an imaging system with diffuse reflection mode is constructed using detectors as receivers, enabling defined scanning images in a high temperature environment. The bifunctional FAPbBr3 SC detectors will motivate new strategies for stable detection in an extreme space environment.

Cesium Doping for Performance Improvement of Lead(II)-acetate-Based Perovskite Solar Cells.

Lead(II)-acetate (Pb(Ac)2) is a promising lead source for the preparation of organolead trihalide perovskite materials, which avoids the use of inconvenient anti-solvent treatment. In this study, we investigated the effect of cesium doping on the performance of Pb(Ac)2-based perovskite solar cells (PSCs). We demonstrate that the quality of the CH3NH3PbI3 perovskite film was improved with increased crystallinity and reduced pinholes by doping the perovskite with 5 mol% cesium. As a result, the power conversion efficiency (PCE) of the PSCs was improved from 14.1% to 15.57% (on average), which was mainly induced by the significant enhancements in short-circuit current density and fill factor. A PCE of 18.02% was achieved for the champion device of cesium-doped Pb(Ac)2-based PSCs with negligible hysteresis and a stable output. Our results indicate that cesium doping is an effective approach for improving the performance of Pb(Ac)2-based PSCs.

Upconversion Plasmonic Lasing from an Organolead Trihalide Perovskite Nanocrystal with Low Threshold

The understanding of nonlinear light–matter interactions at the nanoscale has fueled worldwide interest in upconversion emission for imaging, lasing, and sensing. Upconversion lasers with anti-Stok...

In situ NMR Investigation of the Photoresponse of Perovskite Crystal

Summary Hybrid perovskites are outstanding candidates for use in optoelectronic devices. Nonetheless, hybrid perovskites present numerous fundamental issues that are not yet fully understood. This study seeks to address this problem by reporting on the occurrence of ultraslow dynamic orientation changes in the methylammonium (MA) cations and the corresponding changes in the inorganic lattice of MAPbI3 perovskite crystals occurring over a time scale of 100 s under continuous illumination based on in situ single-crystal 2H nuclear magnetic resonance and in situ X-ray diffraction results. The demonstrated ultraslow dynamic changes in MAPbI3 are far slower than elementary molecular motions typically having time scales of femtoseconds and picoseconds and have never been reported previously. The ultraslow dynamic changes have been correlated with the reduction of band gap and the increase of absorption coefficient of MAPbI3, providing the molecular origins of the stabilization process in the photoresponse of the MAPbI3 device.

A Highly Sensitive Single Crystal Perovskite-Graphene Hybrid Vertical Photodetector.

Organolead trihalide perovskites have attracted significant attention for optoelectronic applications due to their excellent physical properties in the past decade. Generally, both grain boundaries in perovskite films and the device structure play key roles in determining the device performance, especially for horizontal-structured device. Here, the first optimized vertical-structured photodetector with the perovskite single crystal MAPbBr3 as the light absorber and graphene as the transport layer is shown. The hybrid device combines strong photoabsorption characteristics of perovskite and high carrier mobility of flexible graphene, exhibits excellent photoresponse performance with high photoresponsivity (≈1017.1 A W-1 ) and high photodetectivity (≈2.02 × 1013 Jones) in a low light intensity (0.66 mW cm-2 ) under the actuations of 3 V bias and laser irradiation at 532 nm. In particular, an ultrahigh photoconductive gain of ≈2.37 × 103 is attained because of fast charge transfer in the graphene and large recombination lifetime in the perovskite single crystal. The vertical architecture combining perovskite crystal with highly conductive graphene offers opportunities to fulfill the synergistic effect of perovskite and 2D materials, is thus promising for developing high-performance electronic and optoelectronic devices.

Facile and noninvasive passivation, doping and chemical tuning of macroscopic hybrid perovskite crystals

Halide vacancies and associated metallic lead (Pb°) observed at the surface and deep inside macroscopic organolead trihalide perovskite crystals is removed through a facile and noninvasive treatment. Indeed, Br2 vapor is shown to passivate Br-vacancies and associated Pb° in the bulk of macroscopic crystals. Controlling the exposure time can markedly improve the overall stoichiometry for moderate exposures or introduce excessive bromide for long exposures, resulting in p-doping of the crystals. In the low dose passivation regime, Hall effect measurements reveal a ca. 3-fold increase in carrier mobility to ca. 15 cm2V-1s-1, while the p-doping increases the electrical conductivity ca. 10000-fold, including a 50-fold increase in carrier mobility to ca. 150 cm2V-1s-1. The ease of diffusion of Br2 vapor into macroscopic crystals is ascribed to the porosity allowed in rapidly grown crystals through aggregative processes of the colloidal sol during growth of films and macroscopic crystals. This process is believed to form significant growth defects, including open voids, which may be remnants of the escaping solvent at the solidification front. These results suggest that due to the sol-gel-like nature of the growth process, macroscopic perovskite crystals reported in this study are far from perfect and point to possible pathways to improving the optoelectronic properties of these materials. Nevertheless, the ability of the vapor-phase approach to access and tune the bulk chemistry and properties of nominally macroscopic perovskite crystals provides interesting new opportunities to precisely manipulate and functionalize the bulk properties of hybrid perovskite crystals in a noninvasive manner.

Machine-Learning-Accelerated Perovskite Crystallization

Summary Perovskites have seen significant research interest in the last decade. As ternary and quaternary compounds, their chemical space is exceptionally large, yet perovskite development has been limited to a restricted set of chemical constituents often discovered through trial and error. Here, we report a high-throughput experimental framework for the discovery of new perovskite single crystals. We use machine learning (ML) to guide the sequence of ever-improved robotic synthetic trials. We perform high-throughput syntheses of perovskite single crystals with a protein crystallization robot and characterize the outcomes with the aid of convolutional neural network-based image recognition. We then use an ML model to predict the optimal conditions for the synthesis of a new perovskite single crystal, enabling us to report the first synthesis of (3-PLA)2PbCl4.This material exhibits strong blue emission, illustrating the applicability of the method in identifying new optoelectronic materials.

Light-Enhanced Spin Diffusion in Hybrid Perovskite Thin Films and Single Crystals.

Organolead trihalide perovskites have attracted substantial interest with regard to applications in charge-based photovoltaic and optoelectronic devices because of their low processing costs and remarkable light absorption and charge transport properties. Although spin is an intrinsic quantum descriptor of a particle and spintronics has been a central research theme in condensed matter physics, few studies have explored the spin degree of freedom in the emerging hybrid perovskites. Here, we report the characterization of a spin valve that uses hybrid perovskite films as the spin-transporting medium between two ferromagnetic electrodes. Because of the light-responsive nature of the hybrid perovskite, a high magnetoresistance of 97% and a large spin-diffusion length of 81 nm were achieved at 10 K under light illumination in polycrystalline films. Furthermore, by using thin perovskite single crystals, we discovered that the spin-diffusion length was able to reach 1 μm at low temperatures. Our results indicate that the spin relaxation is not significant as previously expected in such lead-containing materials and demonstrate the potential of low-temperature-processed hybrid perovskites as new active materials in spintronic devices.

Improving the performance of lead-acetate-based perovskite solar cells using solvent controlled crystallization process

Lead accetate is an important lead source for preparation of organolead trihalide perovskites. In this work, we improved the performance of lead accetate based perovskite solar cells (PSCs) using a mix-solvent of γ-butyrolactone/dimethyl-sulfoxide (GBL/DMSO). Compared with the use of N,N-dimethylformamide (DMF)/DMSO, using GBL/DMSO efficiently retarded the crystallization of perovskite, which improved the crystallinity of the perovskite films. Consequently, the perovskite films processed from GBL/DMSO showed higher light harvesting, longer carrier lifetime and suppressed charge recombination properties in the PSCs. Power conversion efficiency (PCE) of the PSCs was significantly improved from 16.6 to 17.7% with simultaneous improvement in open-circuit voltage, short-circuit current density and fill factor. The best PSC showed a champion PCE of 18.1%, with a stable power output and negligible hysteresis. Moreover, the flexible PSCs (based on polyethylene naphthalate substrates) with perovskite processed from GBL/DMSO exhibited a high PCE of 13.2%. Our results indicate that using GBL/DMSO as a mix-solvent is a simple and effective way for performance improvement of lead-acetate-based PSCs.

Achieving Small Exciton Binding Energies in Small Molecule Acceptors for Organic Solar Cells: Effect of Molecular Packing.

Because of strong exciton binding energy (Eb), an exciton dissociation process and extra energy losses are present in organic solar cells relative to inorganic and perovskite solar cells. Here, we calculated the Eb of a series of small molecule acceptors in solid crystals by a self-consistent quantum mechanics/embedded charge approach. The results show that the Eb values are substantially reduced from the gas phase to solid state because of electronic polarization (mainly from the induction effect of charges). Moreover, in contrast to little changes in the gas phase, the Eb in the solid state can vary significantly, indicating an important molecular packing effect. Remarkably, an extremely weak Eb of 0.04 eV is achieved in a three-dimensional packing crystal, which is comparable to the Eb of organo-lead trihalide perovskites. This work underlines the importance of three-dimensional molecular packing for achieving small Eb and will be helpful in reducing energy losses in organic solar cells.

Highly sensitive X-ray detector made of layered perovskite-like (NH4)3Bi2I9 single crystal with anisotropic response

The effective detection of X-ray radiation with low threshold is essential to many medical and industrial applications. Three-dimensional (3D) organolead trihalide and double perovskites have been shown to be suitable for direct X-ray detection. However, the sensitivity and stability of 3D perovskite X-ray detectors are limited by ion motion, and there remains a demand to develop green and stable X-ray detectors with high sensitivity and low detection limit. The emerging low-dimensional perovskites have shown promising optoelectronic properties, featuring good intrinsic stability and reduced ion migration. Inspired by this, we show that our 2D layered perovskite-like (NH4)3Bi2I9 device provides unique anisotropic X-ray detecting performance with different crystal directions, effective suppression of ion migration and a low detection limit of 55 nGyair s−1. These results will motivate new strategies to achieve a high-performance X-ray detector by utilizing 2D layered perovskite or perovskite-like materials, without requiring toxic elements. Perovskite-like materials enable different X-ray detection performance along different crystal directions. A low detection limit of 55 nGyair s−1 is demonstrated.

High-Performance Inverted Perovskite Solar Cells Using Doped Poly(triarylamine) as the Hole Transport Layer

Organolead trihalide perovskite materials have attracted considerable interest because of their successful application in fabricating high-efficiency photovoltaic cells. Charge transport layers pla...

Reduced-Dimensional α-CsPbX3 Perovskites for Efficient and Stable Photovoltaics

Summary Inorganic CsPbX3 perovskites have gained great attention owing to their excellent thermal stability and carrier transport properties. However, the power conversion efficiency (PCE) of solution-processed CsPbX3 perovskite solar cells is still far inferior to that of their hybrid analogues. Insufficient film thickness and undesirable phase transition are the two major obstacles limiting their device performance. Here, we show that by adopting a new precursor pair, cesium acetate (CsAc) and hydrogen lead trihalide (HPbX3), we were able to overcome the notorious solubility limitation for Cs precursors to fabricate high-quality CsPbX3 perovskite films with large film thickness (∼500 nm). We further introduced a judicious amount of phenylethylammonium iodide (PEAI) into the system to induce reduced-dimensional perovskite formation. Unprecedentedly, the resulting quasi-2D perovskites significantly suppressed undesirable phase transition and thus reduced the film's trap density. Following this approach, we reported a state-of-the-art PCE to date, 12.4%, for reduced-dimensional α-CsPbI3 perovskite photovoltaics with greatly improved performance longevity.

Perovskites: Between the Grains

Defect reduction and device stabilization will continue to be two important thrusts toward efficient long-lasting polycrystalline perovskite solar cells. Recently in Chem, Zong et al. show that a complementary hydrophobic/hydrophilic triblock copolymer continuously incorporates into methylammonium lead tri-iodide grain boundaries. This improves solar cell stability and performance, resulting in a stabilized 19.4% power conversion efficiency, 92% of which is retained after 480 hr of continuous 1-sun illumination.