CH3NH3PbI3 Single Crystals Research Articles

Excitonic Properties of 3D Hybrid Organic-Perovskites

A renewed interest in hybrid organic perovskites (HOPs) has emerged since 2012 following the increase of HOP solar cell efficiency. Despite the impressive performances of the devices, there is still lot of room for improvement. In particular, the development of applications will benefit of a better understanding of the photophysics of HOPs. In this talk, we will discuss about the excitonic properties of CH3NH3PbI3 (MAPI) single crystals at low temperature, and compare them to those of thin polycrystalline films. The main feature is the appearance of a sharp emission line (FWHM ~ 5 meV) at high energy that is attributed to the free exciton signature, and which is completely absent in thin-films. The observation of the free excitonic emission in the low temperature phase allow to monitor the huge thermal broadening due to electron-LO-phonon coupling [1].

Atomic force microscopy investigation of a step generation and bunching on the (100) facet of a CH3NH3PbI3 crystal, grown from γ‐Butyrolactone

Single crystal of organolead trihalide perovskite (CH3NH3PbI3) is proved to be one of the most promising semiconductor materials. Growing large size and high quality CH3NH3PbI3 single crystals is urgently demanded by photoelectric device applications. However, the growth mechanism in microscopic scale for CH3NH3PbI3 single crystal is still unrevealed. In this paper, we are focusing on observing surface structures on (100) facet of CH3NH3PbI3 single crystal via atomic force microscopy (AFM), especially surface structure conversion related to growth kinetics. The results reveal that the growth of (100) facet of CH3NH3PbI3 single crystal is dependent on bunching steps and step slope. The elemental steps, with step height about 0.45 nm, corresponded to half of the unit cell, are generated from screw dislocations when the growth rate is about 0.2 mm per hour. Elemental steps can bunch together and form bunching steps with growth rate of 0.5 mm per hour, in which only even numbers elementary steps are involved, suggesting even numbers elementary steps are stable than that of odd numbers. Additionally, in terms of the surface structures and solution stabilities, large size and high quality CH3NH3PbI3 single crystals were grown.

Femtosecond Laser Direct Ablating Micro/Nanostructures and Micropatterns on CH3NH3 PbI3 Single Crystal

Single crystal perovskite materials with the intriguing properties of wide optical absorption range, low trap density, photoluminescence, and superior charge-transfer have emerged as a new class of revolutionary photovoltaic semiconductors promising for various applications. A technique to realize microstructures or microdevices on the surface of single crystal can facilitate the incorporation of these materials into optoelectronic applications. Here, we first reported the fabrication of 1-D mciropores, microlines, and 2-D micropatterns such as word “USTC,” number “2016” and “Olympic rings” on the surface of CH3NH3 PbI3 single crystal by femtosecond laser ablating. The effect of parameters such as exposure time, laser peak intensity, and scanning speed was quantitatively investigated to determine the parameter intervals capable of ensuring the required resolution. By fabricating periodic grating microstructures, the perovskite surfaces showed bright iridescence from dark blue to red due to the grating diffraction effect. Moreover, it is found that the fluorescence peak strength of processed area obviously grows with laser peak intensity and scanning speed, which is attributed to the increasing surface roughness caused by higher laser peak intensity and slower scanning speed. These works are beneficial for researchers to better understand the intrinsic property of single crystal perovskite and accelerate perovskite-based optoelectronics applications.

Impact of White Light Illumination on the Electronic and Chemical Structures of Mixed Halide and Single Crystal Perovskites

This study investigates the effect of white light illumination on the electronic and chemical properties of mixed halide perovskite (CH3NH3PbI3−xClx) thin films and CH3NH3PbI3 single crystals using photoelectron and absorption spectroscopy. The pristine materials' surfaces are found to be n‐type because of surface band bending due to the presence of donor levels, likely consisting of reduced lead (Pb0) that acts as surface traps. When illuminating the sample with white light (up to 1 sun), the valence features shifted to lower binding energy due to surface photovoltage, i.e., the bulk of the materials is much less n‐type. However, the surface photovoltage is only partially reversible and vanishes for prolonged illumination time. Concomitantly, a high concentration of metallic Pb0 is found, which induces strong Fermi‐level pinning and quenching of the surface photovoltage. This is accompanied also by the formation of PbI2 defects. Similar experiments on single crystals reveal the presence of a high concentration of reduced (metallic) Pb0 at the sample surface after cleaving. The present findings indicate that the chemical and electronic properties of perovskite films are very sensitive to white light illumination. Accounting for these light‐induced material changes is important to fully understand its photophysical properties and for improving the lifetime of perovskite‐based devices.

Quantification of re-absorption and re-emission processes to determine photon recycling efficiency in perovskite single crystals

Photon recycling, that is, iterative self-absorption and re-emission by the photoactive layer itself, has been speculated to contribute to the high open-circuit voltage in several types of high efficiency solar cells. For organic–inorganic halide perovskites that have yielded highly efficient photovoltaic devices, however, it remains unclear whether the photon recycling effect is significant enough to improve solar cell efficiency. Here we quantitatively evaluate the re-absorption and re-emission processes to determine photon recycling efficiency in hybrid perovskite with its single crystals by measuring the ratio of the re-emitted photons to the initially excited photons, which is realized by modulating their polarization to differentiate them. The photon recycling efficiencies are revealed to be less than 0.5% in CH3NH3PbI3 and CH3NH3PbBr3 single crystals under excitation intensity close to one sun, highlighting the intrinsically long carrier recombination lifetime instead of the photon-recycling-induced photon propagation as the origin of their long carrier diffusion length.

Electron\u2013acoustic phonon coupling in single crystal CH3NH3PbI3 perovskites revealed by coherent acoustic phonons

Despite the great amount of attention CH3NH3PbI3 has received for its solar cell application, intrinsic properties of this material are still largely unknown. Mobility of charges is a quintessential property in this aspect; however, there is still no clear understanding of electron transport, as reported values span over three orders of magnitude. Here we develop a method to measure the electron and hole deformation potentials using coherent acoustic phonons generated by femtosecond laser pulses. We apply this method to characterize a CH3NH3PbI3 single crystal. We measure the acoustic phonon properties and characterize electron-acoustic phonon scattering. Then, using the deformation potential theory, we calculate the carrier intrinsic mobility and compare it to the reported experimental and theoretical values. Our results reveal high electron and hole mobilities of 2,800 and 9,400 cm2 V−1 s−1, respectively. Comparison with literature values of mobility demonstrates the potential role played by polarons in charge transport in CH3NH3PbI3.

Anisotropic moisture erosion of CH3NH3PbI3single crystals

The anisotropy of moisture erosion was observed in CH3NH3PbI3 single crystals. When exposed to moisture, the (001) facet exhibited greater sensitivity to water molecules and showed a faster erosion rate compared to the (100) facet and (112) facet. Structural and chemical origins responsible for anisotropic moisture erosion were elucidated.

Extra long electron–hole diffusion lengths in CH3NH3PbI3−xClxperovskite single crystals

Both trap-state densities and energy levels affect carrier transfer, resulting in a maximum diffusion length of 380 μm in CH3NH3PbI3−xClx(x= 0.005).

Ultra-high Seebeck coefficient and low thermal conductivity of a centimeter-sized perovskite single crystal acquired by a modified fast growth method

A centimeter-sized organic–inorganic hybrid lead-based perovskite CH3NH3PbI3(MAPbI3) single crystal was obtained by using a modified fast and inverse-temperature growth method.

Narrow Linewidth Excitonic Emission in Organic-Inorganic Lead Iodide Perovskite Single Crystals.

Hybrid perovskite thin films have demonstrated impressive performance for solar energy conversion and optoelectronic applications. However, further progress will benefit from a better knowledge of the intrinsic photophysics of materials. Here, the temperature-dependent emission properties of CH3NH3PbI3 single crystals are investigated and compared to those of thin polycrystalline films by means of steady-state and time-resolved photoluminescence spectroscopy. Single crystals photoluminescence present a sharp excitonic emission at high energy, with full width at half maximum of only 5 meV, assigned to free excitonic recombination. We highlight a strong thermal broadening of the free excitonic emission, due to exciton-LO-phonon coupling. The emission turned to be very short-lived with a subnanosecond dynamics, mainly induced by the fast trapping of the excitons. The free excitonic emission is completely absent of the thin film spectra, which are dominated by trap state bands.

Free Excitons and Exciton-Phonon Coupling in CH3NH3PbI3 Single Crystals Revealed by Photocurrent and Photoluminescence Measurements at Low Temperatures.

We investigated the exciton-phonon couplings and exciton binding energy in CH3NH3PbI3 (MAPbI3) single crystals using temperature-dependent photocurrent (PC) and photoluminescence (PL) spectroscopy. The PC and PL data provide clear evidence of the existence of excitons in orthorhombic-phase MAPbI3. The temperature-dependent PC data were found to be less influenced by the bound excitons than the PL data, and thus the PC data reflect the intrinsic scatterings of excitons. We observed that the exciton-phonon couplings were strong in MAPbI3 and determined the longitudinal optical phonon energy to be 16.1 meV. Moreover, on the basis of the temperature dependences of the PC and PL data, we evaluated the exciton binding energy to be 12.4 meV for orthorhombic-phase MAPbI3 single crystals. Our findings pave a way for using simultaneous PC and PL measurements to determine precisely fundamental properties of perovskites.

Near infrared photodetectors based on sub‐gap absorption in organohalide perovskite single crystals

AbstractOrganohalide perovskite optoelectronics based upon large (mm‐sized) single crystals present exciting opportunities for new device platforms and fundamental studies. Herein, we report CH3NH3PbBr3 and CH3NH3PbI3 single crystals prepared via an inverse temperature crystallization method with strong near infrared photoresponses significantly below the optical gap. Light intensity dependent photocurrent measurements reveal the photoresponse is not a two‐photon phenomenon, but rather is derived from a linear mechanism. The effect (including responsivity and speed) is enhanced in a photoresistor architecture, indicating that the photoresponse is due to absorption into surface trap states in the crystal. Without any optimisation, respectable NIR responsivities at room temperature of ∼10‐2 A W−1 at a low 1V bias operating voltage are achieved. These results again demonstrate the remarkable potential of organohalide perovskites as light sensing materials, and the possibilities for engineering a new class of single crystal‐based optoelectronics. image

Regulating Carrier Dynamics in Single Crystal Halide Perovskite via Interface Engineering and Optical Doping

High-quality CH3NH3PbI3 single crystals are synthesized with desired intrinsic carrier dynamics revealed by time-resolved photoluminescence spectroscopy and Hall effect measurement. Quantitative anisotropy of electron/hole mobility in CH3NH3PbI3 single crystal is unveiled with a double diode configuration and anisotropic photon illumination. With intentional optical doping, the switching dynamics of the double diode photo­detectors is regulated.

High-quality inorganic–organic perovskite CH3NH3PbI3 single crystals for photo-detector applications

Single crystals of organolead trihalide perovskites (CH3NH3PbI3) are supposed to be one of the most promising materials as photo-detectors. Because of their large absorption coefficient, long-range balanced electron, and hole-transport lengths, it is considered to break through the responsivity and efficiency. To systematically investigate the potentiality as photo-detector, high-quality CH3NH3PbI3 single crystals with large size are highly demanded. In the paper, large CH3NH3PbI3 single crystals with various crystal shapes were grown from γ-butyrolactone. At optimized precursor concentration and growth temperature, the growth rate was fixed at about 0.2 mm h−1. Under such growth conditions, the growth steps, originated from screw dislocation on (100) facet, were revealed to be about 0.45 nm. This value is corresponded to half of the unit cell, implying the slow growth rate of (100) facet. With slow growth rate, the absorption edge of the CH3NH3PbI3 single crystal was extended to 860 nm, correlated with a calculated bandgap of ~1.44 eV. By depositing a pair of Au electrodes, a metal–semiconductor–metal (MSM) photo-detector on the basis of the CH3NH3PbI3 single crystal active layer (3 mm) was fabricated and its photo-response features were investigated systematically. About 2.531 A W−1 responsivity was obtained from the device under 780 nm laser illumination, while the external quantum efficiency reached to 396.20 %, better than some GaN, GaAs, and GaP photo-detectors with a MSM device structure.

Perovskite CH3NH3PbI3(Cl) Single Crystals: Rapid Solution Growth, Unparalleled Crystalline Quality, and Low Trap Density toward 10(8) cm(-3).

Single crystal reflects the intrinsic physical properties of a material, and single crystals with high-crystalline quality are highly desired for the acquisition of high-performance devices. We found that large single crystals of perovskite CH3NH3PbI3(Cl) could be grown rapidly from chlorine-containing solutions. Within 5 days, CH3NH3PbI3(Cl) single crystal as large as 20 mm × 18 mm × 6 mm was harvested. As a most important index to evaluate the crystalline quality, the full width at half-maximum (fwhm) in the high-resolution X-ray rocking curve (HR-XRC) of as-grown CH3NH3PbI3(Cl) single crystal was measured as 20 arcsec, which is far superior to so far reported CH3NH3PbI3 single crystals (∼1338 arcsec). The unparalleled crystalline quality delivered a low trap-state density of down to 7.6 × 10(8) cm(-3), high carrier mobility of 167 ± 35 cm(2) V(-1) s(-1), and long transient photovoltaic carrier lifetime of 449 ± 76 μs. The improvement in the crystalline quality, together with the rapid growth rate and excellent carrier transport property, provides state-of-the-art single crystalline hybrid perovskite materials for high-performance optoelectronic devices.

Perovskite Photodetectors based on CH3 NH3 PbI3 Single Crystals.

As very important light-harvesting materials, organic-inorganic perovskites have showed an alluring prospect in optoelectronic devices. However, most of the perovskite devices, such as photodetectors reported recently, are based on the polycrystalline films of perovskites, and the large grain boundaries and amounts of defects existing in films are unfavorable for the further improvement of device performance. Herein, high-quality single crystals of CH3 NH3 PbI3 were successfully prepared through a simple solution immersing method. The obtained CH3 NH3 PbI3 crystals showed the morphologies of nanowires and nanoplates, which were confirmed to belong to the same tetragonal phase. Both nanowire- and nanoplate-based photodetectors exhibited improved performance over CH3 NH3 PbI3 polycrystalline thin films, with an on/off ratio approaching 103 , which is one of the highest values reported so far for perovskite photodetectors.

Amplified Spontaneous Emission from Organic–Inorganic Hybrid Lead Iodide Perovskite Single Crystals under Direct Multiphoton Excitation

Amplified spontaneous emission is observed from the orthorhombic and tetragonal phases of the solution-grown bulk CH3NH3PbI3 single crystals under simultaneous two- and three-photon excitations over a range of operation temperature. The nonlinear optical properties of the crystal are also investigated by measuring the two- and three-photon absorption coefficients of the bulk crystals at room-temperature using the Z-scan technology. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Charge Carrier Lifetimes Exceeding 15 μs in Methylammonium Lead Iodide Single Crystals.

The charge carrier lifetime in organic-inorganic perovskites is one of the most important parameters for modeling and design of solar cells and other types of devices. In this work, we use CH3NH3PbI3 single crystal as a model system to study optical absorption, charge carrier generation, and recombination lifetimes. We show that commonly applied photoluminescence lifetime measurements may dramatically underestimate the intrinsic carrier lifetime in CH3NH3PbI3, which could be due to severe charge recombination at the crystal surface and/or fast electron-hole recombination close to the surface. By using the time-resolved microwave conductivity technique, we investigated the lifetime of free mobile charges inside the crystals. Most importantly, we find that for homogeneous excitation throughout the crystal, the charge carrier lifetime exceeds 15 μs. This means that the diffusion length in CH3NH3PbI3 can be as large as 50 μm if it is no longer limited by the dimensions of the crystallites.

Controllable growth of bulk cubic-phase CH3NH3PbI3single crystal with exciting room-temperature stability

To obtain bulk cubic CH3NH3PbI3, chlorobenzene was employed to regulate the CH3NH3PbI3 γ-butyrolactone solution with high saturated solubility at room temperature and a high yield of crystal at 60 °C. As a result, bulk cubic CH3NH3PbI3 single crystal was successfully synthesized for the first time in mixed-solvent method at 60 °C, which is a little higher than the tetragonal–cubic phase inversion temperature.

A self-powered photodetector based on a CH3NH3PbI3single crystal with asymmetric electrodes

Methylammonium lead iodide perovskite (MAPbI3) has made a re-entry into the literature nowadays for its extraordinary characteristics, such as high absorption of light, long carrier diffusion length, high carrier mobility, low trap-state density, low surface recombination velocity and ease of attainment. Here, we report a self-powered photodetector based on a CH3NH3PbI3 single crystal by employing asymmetric Au–Al electrodes. The key issue of this photodetector was the metal–semiconductor contacts, owing to the Schottky junction between them. By setting the channel length between the Au–Al electrodes to 30 μm for sufficient electron–hole pair separation and transportation, the device showed good performance under 1 sun illumination. The short-circuit photocurrent density and open-circuit voltage were 6.86 mA cm−2 and 0.7 V, respectively. The photocurrent was almost 2 orders of magnitude larger than that based on a perovskite polycrystalline film with a similar device structure. More importantly, the device could detect the lowest noticeable incident power density down to 1 × 10−8 W cm−2. Under this weak light intensity, the responsivity was as high as 0.24 A W−1 without any bias. The photoresponse also had a broadband ranging from 375 nm to 808 nm accompanied by a fast response speed.