Hybrid Organic-inorganic Lead Halide Perovskites Research Articles

Self-Seeding Growth for Perovskite Solar Cells with Enhanced Stability

Summary Hybrid organic-inorganic lead halide perovskite solar cells have shown a remarkable rise in power conversion efficiency over a short period of time; however, long-term stability remains a key challenge hindering the practical application of these cells. Here, we report an approach to sequentially apply a typical one-step solution formulation—self-seeding growth (SSG)—to realize high-quality perovskite thin films with reduced defect density, fewer apparent grain boundaries, improved charge-carrier transport and lifetime, and enhanced hydrophobicity for enhanced stability. Using FA-MA-Cs-based perovskite, SSG devices showed improved efficiency from 17.76% (control) to 20.30% (SSG), with an unencapsulated device retaining >80% of its initial efficiency over 4,680-h storage in an ambient environment with high relative humidities. The SSG devices also exhibited much improved thermal and operational stabilities. In addition, SSG can be applied to different substrates and perovskite compositions, which makes it a viable method for preparing high-quality perovskite thin films for device applications.

Direct-Bandgap 2D Silver-Bismuth Iodide Double Perovskite: The Structure-Directing Influence of an Oligothiophene Spacer Cation.

Three-dimensional (3D) hybrid organic-inorganic lead halide perovskites (HOIPs) feature remarkable optoelectronic properties for solar energy conversion but suffer from long-standing issues of environmental stability and lead toxicity. Associated two-dimensional (2D) analogues are garnering increasing interest due to superior chemical stability, structural diversity, and broader property tunability. Toward lead-free 2D HOIPs, double perovskites (DPs) with mixed-valent dual metals are attractive. Translation of mixed-metal DPs to iodides, with their prospectively lower bandgaps, represents an important target for semiconducting halide perovskites, but has so far proven inaccessible using traditional spacer cations due to either intrinsic instability or formation of competing non-perovskite phases. Here, we demonstrate the first example of a 2D Ag-Bi iodide DP with a direct bandgap of 2.00(2) eV, templated by a layer of bifunctionalized oligothiophene cations, i.e., (bis-aminoethyl)bithiophene, through a collective influence of aromatic interactions, hydrogen bonding, bidentate tethering, and structural rigidity. Hybrid density functional theory calculations for the new material reveal a direct bandgap, consistent with the experimental value, and relatively flat band edges derived principally from Ag-d/I-p (valence band) and Bi-p/I-p (conduction band) states. This work opens up new avenues for exploring specifically designed organic cations to stabilize otherwise inaccessible 2D HOIPs with potential applications for optoelectronics.

Chiral 2D Perovskites with a High Degree of Circularly Polarized Photoluminescence.

Chiral materials are of particular interest and have a wide range of potential applications in life science, material science, spintronic, and optoelectronic devices. Two-dimensional (2D) hybrid organic-inorganic lead halide perovskites have attracted increasing attention. Incorporating the chiral organic ligands into the layered lead iodide frameworks would introduce strong chirality in pure 2D perovskites for potential applications in circularly polarized light (CPL) emission and detection; nonetheless, studies on those aspects are still in their infancy. Here, we report on the strong CPL emission and sensitive CPL detection in the visible-wavelength range in pure chiral ( R-/ S-MBA)2PbI4 (MBA = C6H5C2H4NH3) 2D perovskites, which are successfully synthesized with a needle shape and millimeter size by incorporating the chiral molecules. The chiral 2D perovskites ( R-MBA)2PbI4 and ( S-MBA)2PbI4 exhibit an average degree of circularly polarized photoluminescence (PL) of 9.6% and 10.1% at 77 K, respectively, and a maximum degree of the circularly polarized PL of 17.6% is achieved in ( S-MBA)2PbI4. The degree of circularly polarized PL dramatically decreases with increasing temperature, implying that the lattice distortion induced by the incorporated chiral molecules and/or temperature-dependent spin flipping might be the origin for the observed chirality. Finally, CPL detection has been achieved with decent performance in our chiral 2D perovskite microplate/MoS2 heterostructural devices. The high degree of the circularly polarized PL and excellent CPL detection together with the layered nature of pure chiral 2D perovskites enables them to be a class of very promising materials for developing and exploring spin associated electronic devices based on the chiral 2D perovskites.

Continuous wave amplified spontaneous emission in phase-stable lead halide perovskites

Sustained stimulated emission under continuous-wave (CW) excitation is a prerequisite for new semiconductor materials being developed for laser gain media. Although hybrid organic-inorganic lead-halide perovskites have attracted much attention as optical gain media, the demonstration of room-temperature CW lasing has still not been realized. Here, we present a critical step towards this goal by demonstrating CW amplified spontaneous emission (ASE) in a phase-stable perovskite at temperatures up to 120 K. The phase-stable perovskite maintains its room-temperature phase while undergoing cryogenic cooling and can potentially support CW lasing also at higher temperatures. We find the threshold level for CW ASE to be 387 W cm-2 at 80 K. These results indicate that easily-fabricated single-phase perovskite thin films can sustain CW stimulated emission, potential at higher temperatures as well, by further optimization of the material quality in order to extend the carrier lifetimes.

A two-dimensional organic-inorganic hybrid perovskite-type semiconductor: poly[(2-azaniumylethyl)trimethylphosphanium [tetra-μ-bromido-plumbate(II)]

Recently, with the prevalence of `perovskite fever', organic-inorganic hybrid perovskites (OHPs) have attracted intense attention due to their remarkable structural variability and highly tunable properties. In particular, the optical and electrical properties of organic-inorganic hybrid lead halides are typical of the OHP family. Besides, although three-dimensional hybrid perovskites, such as [CH3NH3]PbX3 (X = Cl, Br or I), have been reported, the development of new organic-inorganic hybrid semiconductors is still an area in urgent need of exploration. Here, an organic-inorganic hybrid lead halide perovskite is reported, namely poly[(2-azaniumylethyl)trimethylphosphanium [tetra-μ-bromido-plumbate(II)]], {(C5H16NP)[PbBr4]}n, in which an organic cation is embedded in inorganic two-dimensional (2D) mesh layers to produce a sandwich structure. This unique sandwich 2D hybrid perovskite material shows an indirect band gap of ∼2.700 eV. The properties of this compound as a semiconductor are demonstrated by a series of optical characterizations and indicate potential applications for optical devices.

Influence of Cl Incorporation in Perovskite Precursor on the Crystal Growth and Storage Stability of Perovskite Solar Cells.

Solar cells based on organic-inorganic hybrid lead-halide perovskites are very promising because of their high performance and solution process feasibility. Elemental engineering on perovskite composition is a facile path to obtain high-quality crystals for efficient and stable solar cells. It was found that partially substituting I- with Cl- in the perovskite precursor promoted crystal growth, with the grain size larger than the layer thickness, and facilitated the generation of a self-passivation layer of PbI2. Whereas the residual Cl- ions were suspected to diffuse to the hole-transport layer consisting of ubiquitously spiro-OMeTAD, the formation of highly bounded ionic pairing of Cl- with the oxidized state of spiro-OMeTAD led to insufficient charge extraction and severely reversible performance degradation. This issue was effectively alleviated upon Br- doping owing to the generation of Pb-Br bonds in the lattice that strengthened the phase stability by improving the binding energy between each unit. The binary halide (Br-/Cl-)-doped perovskites resulted in a champion power conversion efficiency of 20.2% with improved long-term storage stability.

Revealing lattice and photocarrier dynamics of high-quality MAPbBr3 single crystals by far infrared reflection and surface photovoltage spectroscopy

Hybrid organic-inorganic lead halide perovskite materials show great promise in a number of optoelectronic applications, including solar cells, light emitting diodes, and photodetectors. Understanding their intrinsic material properties is critical to enhancing device performance and enabling innovative material and device designs. Here, we study lattice dynamics using far-infrared (FIR) reflectance and photogenerated carrier dynamics using surface photovoltage (SPV) measurements on high-quality methylammonium lead bromide (MAPbBr3) single crystals. FIR reflectance shows three coherent infrared-active phonon modes between 40 and 200 cm−1 that result in reststrahlen bands with much higher peak reflectance than has been previously reported. The phonon mode strength and damping are comparable to classical oxide perovskite single crystals. However, the effects of defects on photogenerated carrier recombination are still evident in SPV measurements. By performing SPV over different spectral ranges, we are able to separate the effects of surface and bulk defects on the recombination dynamics of photogenerated charge carriers. We further apply SPV measurements to obtain the minority carrier (electron) diffusion length for the MAPbBr3 crystal. This study demonstrates that both FIR reflectance and SPV measurements provide useful information on the electromagnetic response properties of halide perovskite single crystals.

Fe2+/Fe3+ Doped into MAPbCl3 Single Crystal: Impact on Crystal Growth and Optical and Photoelectronic Properties

As one type of organic–inorganic hybrid lead halide perovskites, MAPbX3 has attracted immense interests in applications of optoelectronic devices because of its remarkable properties. However, the ...

Enhanced Seebeck Effect of a MAPbBr3 Single Crystal by an Organic and a Metal Modified Layer

AbstractThe organic–inorganic hybrid lead halide perovskite single crystal has drawn much attention of researchers for excellent characteristics, such as more excellent stability than the polycrystalline film. However, during the crystal preparation process, there are inevitably generated surface defect states, which seriously affect the charge transport properties of the single crystal. In this article, the MAPbBr3 single crystal is prepared by the inverse temperature crystallization method, the semiconductor characteristics of the crystal surface defect states are studied by the Seebeck effect method, and the crystal Seebeck coefficient is enhanced. It is confirmed that there are N‐type defect states on the surface of the MAPbBr3 single crystal. Then the organic semiconductor layer and metal surface modified layer are utilized to reduce the concentration of defects and got the enhancement of the Seebeck coefficient of MAPbBr3 single crystal. At last, the Au/MAPbBr3/PFO/Au structure device is designed and prepared to improve the thermoelectric properties of the MAPbBr3 single crystal. Results show that the thermal voltage keeps increasing, and the Seebeck coefficient is also enhanced.

A high performance perovskite CH3NH3PbCl3 single crystal photodetector: benefiting from an evolutionary preparation process

Hybrid organic–inorganic lead halide perovskites (CH3NH3PbX3, X = Cl, Br, or I) are deemed to be the highest potential semiconducting materials due to their unique optoelectronic properties.

Lead-free, stable, and effective double FA4GeIISbIIICl12 perovskite for photovoltaic applications

Organic-inorganic hybrid lead halide perovskite solar cells emerge as a breakthrough photovoltaic technology with high power conversion efficiency. However, some inherent shortcomings impede their further industrialization: 1) the toxicity of Pb, 2) unstable, sensitive to moisture and/or light. To circumvent these issues, we study the lead-free and solution-processed photovoltaic devices based on the double-metals <111>-oriented 2D layered formamidinium germanium-antimony halide perovskites (FA4GeIISbIIICl12) in this contribution. Compared with benchmark MAPbI3, the larger formamidinium is selected to replace methylammonium to form a more stable crystal structure while the double metals germanium-antimony (GeII-SbIII) are chosen to replace Pb under the considerations that expanding the possible metal combinations in the design of new perovskite with analogous photovoltaic performance. The FA4GeIISbIIICl12 perovskite behaves as a stable and efficient semiconductor with direct bandgap of ~ 1.3 eV and its conductivity is one order of magnitude higher than that of MAPbI3. Meanwhile, FA4GeIISbIIICl12 based solar cell with power conversion efficiency up to 4.7% can be achieved without use of any additives. This approach opens up new possibilities of exploiting lead-free perovskite that incorporates metals in different valence states and offers great potential application in photoelectric field.

First-Principle Insights of Electronic and Optical Properties of Cubic Organic–Inorganic MAGexPb(1–x)I3 Perovskites for Photovoltaic Applications

Owing to power conversion efficiencies of as high as 22.1%, hybrid organic–inorganic lead halide perovskites have become the fastest growing solar technology, competing with the conventional thin-f...

Improving the Bulk Emission Properties of CH3NH3PbBr3 by Modifying the Halide-Related Defect Structure

The peculiar defect chemistry of hybrid organic–inorganic lead halide perovskites is believed to be partially responsible for the outstanding performance of this solution-processed material in optoelectronic devices. While most effort has been put on the management of halide defects (the ones presenting the highest mobility) for CH3NH3PbI3, its bromide counterpart has not been so widely studied. Although the former is the material of choice for photovoltaics, the latter is present in most light-emitting applications. Here, we report how the exposure of CH3NH3PbBr3 single crystals to a bromine atmosphere strongly affects its emission properties. Such improvement takes place in the absence of apparent signs of degradation and remains for tens of hours. We propose an explanation based on the defect structure for this material where bromine-related defects can act as deep or shallow traps. These results are of relevance for a material expected to be present in a new generation of solution-processed light-emitting devices.

New Tin(II) Fluoride Derivative as a Precursor for Enhancing the Efficiency of Inverted Planar Tin/Lead Perovskite Solar Cells

Hybrid organic-inorganic lead halide perovskite has become one of the most attractive materials for future low-cost and high-efficiency solar technology. However, serious concern about the content ...

Inorganic and Lead-Free AgBiI4 Rudorffite for Stable Solar Cell Applications

Organic–inorganic hybrid lead halide perovskites have recently realized significant development. However, the toxicity of lead (Pb) and the poor stability might eventually hamper the commercialization of perovskite solar cells (PSCs). Here, we present an environment friendly and stable all inorganic rudorffite AgBiI4 as solar absorber by solution-based synthesis of thin-films. AgBiI4 films fabricated by 0.6 M solution and annealed at 150 °C show dense grains and high surface coverage. Furthermore, the AgBiI4 films exhibit greater thermal stability and photostability than CH3NH3PbI3. Ultimately, by judiciously choosing the hole transport material with appropriate energy level, the solar cell device demonstrates high carrier extraction efficiency and achieve a power conversion efficiency (PCE) of 2.1% under standard 1 sun (AM 1.5). The devices also show excellent long-term air stability and still maintain 96% of its initial PCE even after 1000h at relative humidity of 26%. This work highlights new direction...

Nanocomposite perovskite based optical sensor with broadband absorption spectrum

Recently, organic-inorganic hybrid lead halide perovskite optical sensors have attracted lots of attention for their unique and remarkable optoelectronic properties like low-cost solution process deposition. Also, inorganic nanoparticles with narrow bandgap as photocarrier generator has been used in high efficiency low cost optical sensors to increase absorption spectrum. In this paper, we designed and fabricated a solution processed optical sensor by using nanocomposite of Methylammonium lead iodide and PbS nanoparticles as the active layer. It has high absorption in the broad range of spectrum that can work in small driving voltages (less than 1 V). It has low dark current and high photocurrent that are important parameters in optical sensors. This device achieves excellent photoresponsivity and high external quantum efficiency for broad range of wavelength from 370 nm to 940nm.

Nanochannel-Assisted Perovskite Nanowires: From Growth Mechanisms to Photodetector Applications.

Growing interest in hybrid organic-inorganic lead halide perovskites has led to the development of various perovskite nanowires (NWs), which have potential use in a wide range of applications, including lasers, photodetectors, and light-emitting diodes (LEDs). However, existing nanofabrication approaches lack the ability to control the number, location, orientation, and properties of perovskite NWs. Their growth mechanism also remains elusive. Here, we demonstrate a micro/nanofluidic fabrication technique (MNFFT) enabling both precise control and in situ monitoring of the growth of perovskite NWs. The initial nucleation point and subsequent growth path of a methylammonium lead iodide-dimethylformamide (MAPbI3·DMF) NW array can be guided by a nanochannel. In situ UV-vis absorption spectra are measured in real time, permitting the study of the growth mechanism of the DMF-mediated crystallization of MAPbI3. As an example of an application of the MNFFT, we demonstrate a highly sensitive MAPbI3-NW-based photodetector on both solid and flexible substrates, showing the potential of the MNFFT for low-cost, large-scale, highly efficient, and flexible optoelectronic applications.

Low-Temperature Processable Charge Transporting Materials for the Flexible Perovskite Solar Cells

Organic–inorganic hybrid lead halide perovskites have been extensively investigated for various optoelectronic applications. Particularly, owing to their ability to form highly crystalline and homogeneous films utilizing low-temperature solution processes ( 400 °C), has limited the fabrication of perovskite solar cells on flexible substrates. Therefore, the development of a low-temperature processable charge-transporting layer has emerged as an urgent task for achieving flexible perovskite solar cells. This review summarizes the recent progress in low-temperature processable electron- and hole-transporting layer materials, which contribute to improved device performance in flexible perovskite solar cells.

Correction to "Exciton-Dominated Core-Level Absorption Spectra of Hybrid Organic-Inorganic Lead Halide Perovskites".

Correction to "Exciton-Dominated Core-Level Absorption Spectra of Hybrid Organic-Inorganic Lead Halide Perovskites".

Elucidating Surface and Bulk Emission in 3D Hybrid Organic–Inorganic Lead Bromide Perovskites

AbstractThree dimensional (3D) hybrid organic–inorganic lead halide perovskites (HOIP) have emerged in recent years as promising materials for a wide variety of optoelectronic applications. However, the photoluminescence energies in bromide‐based HOIP have been reported to vary in the range from 2.16 to 2.35 eV. The occurrence of surface reconstructions due to uncompensated surface ionic charges may change the photo‐physical properties of the surface regions, but this has not been studied in detail. Herein, by performing angle‐dependent photoluminescence (PL) and spectroscopic ellipsometry of single‐crystal as well as polycrystalline HOIP crystals, the intrinsic excitonic emissions from the surface and bulk regions are clearly identified. It is verified that the high energy PL at 2.31 eV originates from a phase‐modified surface region. The large absorption coefficient of perovskite results in signal depletion of the lower energy PL at 2.16 eV, which originates from the bulk. High resolution synchrotron X‐ray diffraction reveals that air‐exposed HOIP crystals form a multilayer structure consisting of PbBr2, and an interfacial layer of orthorhombic phase, while the bulk crystal remains cubic phase. This study provides the unambiguous identification of a phase‐modified surface region with a larger band gap than the bulk and which dominates the excitonic emission in HOIP crystals.