Defects are generally regarded to have negative impacts on carrier recombination, charge-transport and ion migration in materials, which thus lower the efficiency, speed and stability of optoelectronic devices. Meanwhile, lots of efforts which focused on minimizing defects have greatly improved the performances of devices. Then, can defects be positive in optoelectronic devices? Herein, relying on in-depth understanding of defect-associated effects in semiconductors, trapping of photo-generated carriers by defects is applied to enlarge photoconductive gain in photodetection. Therefore, the record photoconductive gain, gain-bandwidth product and detection limit were achieved in this photodetector. Exceeding the general concept that defects are harmful, we identify a new view that the defects can be positive in photodetection, which may guide us to design high-performance photodetectors.
Halide perovskites are promising materials for light-emitting and light-harvesting applications. In this context, two-dimensional perovskites such as nanoplatelets or Ruddlesden-Popper and Dion-Jacobson layered structures are important because of their structural flexibility, electronic confinement, and better stability. This review article brings forth an extensive overview of the recent developments of two-dimensional halide perovskites both in the colloidal and non-colloidal forms. We outline the strategy to synthesize and control the shape and discuss different crystalline phases and optoe…
The observation of low energy edge photoluminescence and its beneficial effect on the solar cell efficiency of Ruddlesden-Popper perovskites has unleashed an intensive research effort to reveal its origin. This effort, however, has been met with more challenges as the underlying material structure has still not been identified; new modellings and observations also do not seem to converge. Using 2D (BA)2(MA)2Pb3Br10 as an example, we show that 3D MAPbBr3 is formed due to the loss of BA on the edge. This self-formed MAPbBr3 can explain the reported edge emission under various conditions, while t…
It is thought that growing large, oriented grains of perovskite can lead to more efficient devices. We study MAPbI3 films fabricated via Flash Infrared Annealing (FIRA) consisting of highly oriented, large grains. Domains observed in the SEM are often misidentified with crystallographic grains, but SEM images don't provide diffraction information. We measure the grain size, crystal structure and grain orientation using Electron Back-Scattered Diffraction (EBSD) and we study how these affect the optoelectronic properties as characterized by local photoluminescence (PL) and time-resolved microwa…
Organometallic perovskite is one of the potential materials in the various optoelectronic research fields. This research work demonstrates the synthesis of CH3NH3PbI3-ZnS microrods via one-step spin coating for optoelectronic applications. Incorporation of ZnS in the perovskite material caused bandgap variation in the visible wavelength range.
Previous theoretical calculations show azetidinium has the right radial size to form a 3D perovskite with lead halides [1], and has been shown to impart, as the A-site cation of ABX3 unit, beneficial properties to ferroelectric perovskites [2]. However, there has been very limited research into its use as the cation in lead halide perovskites to date. In this communication we report the synthesis and characterization of azetidinium-based lead mixed halide perovskite colloidal nanocrystals. The mixed halide system is iodine and chlorine unlike other reported nanocrystals in the literature where…
Halide perovskites perform remarkably in optoelectronic devices including tandem photovoltaics. However, this exceptional performance is striking given that perovskites exhibit deep charge carrier traps and spatial compositional and structural heterogeneity, all of which should be detrimental to performance. Here, we resolve this long-standing paradox by providing a global visualisation of the nanoscale chemical, structural and optoelectronic landscape in halide perovskite devices, made possible through the development of a new suite of correlative, multimodal microscopy measurements combining…
Metal halide perovskites single-crystalline thin films (SCTFs) have recently emerged as promising materials for the next generation of optoelectronic devices due to their superior intrinsic properties. However, it is still challenging to transfer and integrate them with other functional materials for hybrid multilayer devices because of their substrate-dependent growth. Herein, a method that allows the SCTFs to be transferred with high quality onto arbitrary substrates has been reported. By introducing hydrophobic treatment to the growth substrates, the adhesion between SCTFs and growth substr…
We demonstrate the critical role of surface recombination in mixed-cation, mixed-halide perovskite, FA0.83Cs0.17Pb(I0.85Br0.15)3. By passivating non-radiative defects with the polymerizable Lewis base (3-aminopropyl)trimethoxysilane (APTMS) we transform these thin films. We demonstrate average minority carrier lifetimes > 4 μs, nearly single exponential monomolecular PL decays, and concomitantly high external photoluminescence quantum efficiencies (>20%, corresponding to ~97% of the maximum theoretical quasi-Fermi-level splitting) at low excitation fluence. We confirm both the composition and …
Point defects in metal halide perovskites play a critical role in determining their properties and optoelectronic performance; however, many open questions remain unanswered. In this work, we apply impedance spectroscopy and deep-level transient spectroscopy to characterize the ionic defect landscape in methylammonium lead triiodide ($MAPbI_3$) perovskites in which defects were purposely introduced by fractionally changing the precursor stoichiometry. Our results highlight the profound influence of defects on the electronic landscape, exemplified by their impact on the device built-in potentia…
Anion exchange offers great flexibility and high precision in phase control, compositional engineering and optoelectronic property tuning. Different from previous successful anion exchange process in liquid solution, herein, we develop a vapor-phase anion-exchange strategy to realize the precise phase and bandgap control of large-scale inorganic perovskites by using gas injection cycle, produing some perovskites such as CsPbCl3 which has never been reported in thin film morphology. Ab-initio calculations also provide the insightful mechanism to understand the impact of anion exchange on tuning…
Owing to the increasing popularity of lead-based hybrid perovskites for photovoltaic (PV) applications, it is crucial to understand their defect physics and its influence on their optoelectronic properties. In this work, we simulate various point defects in pseudo-cubic structures of mixed iodide-bromide and bromide-chloride methylammonium lead perovskites with the general formula MAPbI_{3-y}Br_{y} or MAPbBr_{3-y}Cl_{y} (where y is between 0 and 3), and use first principles based density functional theory computations to study their relative formation energies and charge transition levels. We …
Investigation of (CsMA)NaBiX$_6$ (MA= methylammonium; X=Cl,Br, I) Organic-Inorganic Hybrid Double Perovskites for Optoelectronic Applications: A First Principles Study
Light emission and detection are the two fundamental attributes of optoelectronic communication systems. Until now, both functions have been demonstrated using the p-n diode which is exploited across a wide range of applications. However, due to the competing dynamics of carrier injection and photocarrier collection, with this device light emission and detection are realized separately by switching the direction of the applied electrical bias. Here we use mobile ions in halide perovskites to demonstrate light-emitting photodetection in either condition of applied electrical bias. Our device co…
One of the key challenges for future development of efficient and stable metal halide perovskite solar cells is related to the migration of ions in these materials. Mobile ions have been linked to the observation of hysteresis in the current--voltage characteristics, shown to reduce device stability against degradation and act as recombination centers within the band gap of the active layer. In the literature one finds a broad spread of reported ionic defect parameters (e.g. activation energies) for seemingly similar perovskite materials, rendering the identification of the nature of these spe…
Photovoltaic potential of tin perovskites revealed through layer-by-layer investigation of optoelectronic and charge transport properties
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH（亥姆霍兹柏林材料与能源有限公司）；Egyptian Petroleum Research Institute（埃及石油研究所）；IPVF, Institut Photovoltaïque d'Ile-de-France（法兰西岛光伏研究所）；University of Naples Federico II（那不勒斯费德里科二世大学）；Henan University（河南大学）；University of the Basque Country UPV/EHU（巴斯克国立大学）；Bielefeld University（比勒费尔德大学）
Most traditional semiconductor materials are based on the control of doping densities to create junctions and thereby functional and efficient electronic and optoelectronic devices. The technology development for halide perovskites had initially only rarely made use of the concept of electronic doping of the perovskite layer and instead employed a variety of different contact materials to create functionality. Only recently, intentional, or unintentional doping of the perovskite layer is more frequently invoked as an important factor explaining differences in photovoltaic or optoelectronic per…
All-inorganic lead halide perovskite nanocrystals (NCs) show potential in optoelectronic devices, though their stability and efficiency have yet to improve. In this work, we explore the effect of bivalent metal site doping on the optoelectronic properties of CsPbX$_3$ (X = Br, Cl) perovskite NCs. First, the Pb$^{2+}$ ions in pristine CsPbBr$_3$ NC are partially substituted by Mn$^{2+}$ ions, and the alkaline earth metal strontium is then doped on both pristine and Mn$^{2+}$-substituted particles. The structural and photophysical properties of the pristine and the three doped NC variants have b…
The long-term stability of halide perovskite solar cells (PSCs) remains the critical problem of this photovoltaic technology. Different structural defects formed in the thin-film perovskite films were considered as a main trigger for the decomposition of the absorber and corrosion of the interfaces in the device structure. The changes in the stability performance of the PSCs require a detailed analysis of the defects generated under external stress (light and heat). Using admittance, deep-level transient spectroscopy (DLTS) and reverse DLTS we determined the evolution of the defect energy leve…
Förster Resonant Energy Transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as a new optoelectronic design element to transport energy. However, so far nanocrystal (NC) systems supported only diffusion length of 30 nm, which are too small to be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.5 cm2/s diffusivity through an ordered, two-dimensional assembly of cesium lead bromide perovskite nanocrystals (PNC). Exciton diffusion was directly measured via steady-state and time-resolved pho…
With rapidly growing photoconversion efficiencies, hybrid perovskite solar cells have emerged as promising contenders for next generation, low-cost photovoltaic technologies. Yet, the presence of nanoscale defect clusters, that form during the fabrication process, remains critical to overall device operation, including efficiency and long-term stability. To successfully deploy hybrid perovskites, we must understand the nature of the different types of defects, assess their potentially varied roles in device performance, and understand how they respond to passivation strategies. Here, by correl…
In recent years, metal halide perovskites have generated tremendous interest for optoelectronic applications and their underlying fundamental properties. Due to the large electron-phonon coupling characteristic of soft lattices, self-trapping phenomena are expected to dominate hybrid perovskite photoexcitation dynamics. Yet, while the photogeneration of small polarons was proven in low dimensional perovskites, the nature of polaron excitations in technologically relevant 3D perovskites, and their influence on charge carrier transport, remain elusive. In this study, we used a combination of fir…
Achieving control over the transport properties of charge-carriers is a crucial aspect of realizing high-performance electronic materials. In metal-halide perovskites, which offer convenient manufacturing traits and tunability for certain optoelectronic applications, this is challenging: The perovskite structure itself, poses fundamental limits to maximum dopant incorporation. Here, we demonstrate an organic modifier incorporation strategy capable of modulating the electronic density of states in halide tin perovskites without altering the perovskite lattice, in a similar fashion to substituti…
Electronic states of the hybrid perovskite enable their promising applications as distinctive optoelectronic materials. The understanding of their electronic structures and charge characters remains highly controversial. The electronic mechanism such as reabsorption, Urbach tail and indirect band for interpreting dual-peak emissions is one of the controversial focuses. Herein, we report that through heterojunction enhanced exciton dissociation and global tracing of multiple radiative electronic states across wide temperature regions, we have succeeded in directly observing free carrier emissio…
Halide perovskites have indisputably exceptional optical and electronic properties, which are attractive for next-generation optoelectronic device technologies. We report on a reversible photoluminescence (PL) peak in iodide-based organic-inorganic lead halide perovskite materials under a two-photon absorption (TPA) process, while tuning the excitation wavelength. This phenomenon occurs when the incoming femtosecond (fs) laser photon energy is higher than a threshold energy. Intriguingly, this phenomenon also occurs in other kinds of iodide perovskite materials. Moreover, two more shorter wave…
Superconducting optoelectronic networks could achieve scales unmatched in hardware-based neuromorphic computing. After summarizing recent progress in this area, we report new results in cryogenic silicon photonic light sources, components central to these architectures.
Metal-halide perovskite nanocrystals have demonstrated excellent optoelectronic properties for light-emitting applications. Isovalent doping with various metals (M2+) can be used to tailor and enhance their light emission. Although crucial to maximize performance, an understanding of the universal working mechanism for such doping is still missing. Here, we directly compare the optical properties of nanocrystals containing the most commonly employed dopants, fabricated under identical synthesis conditions. We show for the first time unambiguously and supported by first principles calculations …
Excitonic stimulated emission provides a promising mechanism and route to achieve low-threshold semiconductor lasers for micro-nano optoelectronic integrations. However, excitonic stimulated emission from quantum structure-free semiconductors has rarely been realised at room temperature due to the phase transition between excitonic and electron-hole plasma states. Herein, we show that through trap-state and band-edge engineering, bound exciton states can be stabilised within the hybrid lead bromide perovskite. Under modest pumping conditions, these states enable stimulated emission behaviour t…
Two-dimensional (2D) hybrid organic inorganic perovskite (HOIP) semiconductors have attracted widespread attention as a platform of next generation optoelectronic devices benefiting from their naturally occurring and tunable multiple quantum-well like (QW) structures, which enable a wide range of physical properties. Determining the intrinsic optical/electronic properties of 2D HOIPs is extremely important for further utility in photonic and optoelectronics devices. Here, we obtain the optical dielectric functions, complex refractive indices, and complex optical conductivities of both Ruddlesd…
It is well known that the DX center is a kind of defect that limits the n-type doping in some tetrahedral coordinated semiconductors. It is a deep negatively charged defect complex converted from a nominal shallow donor defect, which can serve as a trap center of electrons, thus is detrimental to the performance of optoelectronic devices. Similar to the DX center, we find that a donor-yielded complex center (DY center) also exists in six-fold coordinated semiconducting materials. For example, Bi is commonly expected as a shallow n-type dopant in perovskite APbX3. However, our first-principles …
Two-dimensional (2D) perovskites or Ruddleson Popper (RP) perovskites have emerged as a class of material inheriting the superior optoelectronic properties of two different materials: perovskites and 2D materials. The large exciton binding energy and natural quantum well structure of 2D perovskite not only make these materials ideal platforms to study light-matter interactions, but also render them suitable for fabrication of various functional optoelectronic devices. Nanoscale structuring and morphology control have led to semiconductors with enhanced functionalities. For example, nanowires o…
Halide perovskites have emerged recently as promising materials for many applications in photovoltaics and optoelectronics. Recent studies of their optical properties suggest many novel opportunities for a design of advanced nanophotonic devices due to low-cost fabrication, high values of the refractive index, existence of excitons at room temperatures, broadband bandgap tunability, high optical gain and nonlinear response, as well as simplicity of their integration with other types of structures. This paper provides an overview of the recent progress in the study of optical effects originatin…
