Halide Perovskite Single Crystals: Optoelectronic Applications and Strategical Approaches

Asymmetrical Electrical Performance across Different Planes of Solution-Grown MAPbBr3 Crystals of mm Dimensions

Throughout a few years, carrier transport studies across HaP single crystals have gained enormous importance for current generation photovoltaic and photodetector research with their superior optoelectronic properties compared to commercially available polycrystalline materials. Utilizing the room-temperature solution-grown method, we synthesized MAPbBr₃ crystals and examined their electrical transport properties. Although the X-ray diffraction reveals the cubical nature of the crystals, we have observed anisotropy in the electrical transport behavior and variation in dielectric constant across the three opposite faces of the crystals of mm dimensions. The face with a higher dielectric constant depicts improved parameters from electrical characteristics such as lower trap densities and higher mobility values. We further explore the origin of its anisotropic nature by performing X-ray diffraction on three opposite faces of crystals. Our studies define the specific faces of cuboid-shaped MAPbBr₃ crystals for efficient electrical contact in the fabrication of optoelectronic devices.

High-Brightness Perovskite Microcrystalline Light-Emitting Diodes

Here a high-brightness perovskite microcrystalline light-emitting diode (LED) is reported, in which the perovskite microcrystals were grown directly on the conductive substrate and a simple metal-insulator-semiconductor structure was adopted. A peak external quantum efficiency of 0.46% was obtained, which is high for perovskite microcrystalline LEDs. Importantly, the maximum luminance of the device reaches 8848.4 cd m^-2, indicating an ultrahigh brightness of >1.2 × 10⁶ cd m^-2 for the microcrystals (corresponding to an ultrahigh current density of 80.9 A cm^-2), because the light-emitting area of the microcrystals accounts for only ∼0.7% of the device area. In addition, we have studied the degradation of the device at a high current density by in situ microscopic observation and found that a severe Joule heating effect at large injection is the primary problem to be solved to realize electrically pumped perovskite microcrystal lasing.

Impact of Cesium Concentration on Optoelectronic Properties of Metal Halide Perovskites

Performance of a perovskite solar cell is largely influenced by the optoelectronic properties of metal halide perovskite films. Here we study the influence of cesium concentration on morphology, crystal structure, photoluminescence and optical properties of the triple cation perovskite film. Incorporation of small amount (x = 0.1) of cesium cations into Csx(MA0.17FA0.83)1−x Pb(I0.83Br0.17)3 leads to enhanced power conversion efficiency (PCE) of the solar cell resulting mainly from significant rise of the short-current density and the fill factor value. Further increase of Cs concentration (x > 0.1) decreases the film’s phase purity, carrier lifetime and correspondingly reduces PCE of the solar cell. Higher concentration of Cs (x ≥ 0.2) causes phase segregation of the perovskite alongside with formation of Cs-rich regions impeding light absorption.

Advanced Polymer and Perovskite Solar Cells

This special issue was designed to draw attention to photovoltaic technology, which harnesses sunlight—the most promising renewable energy source—for our sustainable future [...]

Monocrystalline Methylammonium Lead Halide Perovskite Materials for Photovoltaics

Lead halide perovskite solar cells have been gaining more and more interest. In only a decade, huge research efforts from interdisciplinary communities enabled enormous scientific advances that rapidly led to energy conversion efficiency near that of record silicon solar cells, at an unprecedented pace. However, while for most materials the best solar cells were achieved with single crystals (SC), for perovskite the best cells have been so far achieved with polycrystalline (PC) thin films, despite the optoelectronic properties of perovskite SC are undoubtedly superior. Here, by taking as example monocrystalline methylammonium lead halide, the authors elaborate the literature from material synthesis and characterization to device fabrication and testing, to provide with plausible explanations for the relatively low efficiency, despite the superior optoelectronics performance. In particular, the authors focus on how solar cell performance is affected by anisotropy, crystal orientation, surface termination, interfaces, and device architecture. It is argued that, to unleash the full potential of monocrystalline perovskite, a holistic approach is needed in the design of next-generation device architecture. This would unquestionably lead to power conversion efficiency higher than those of PC perovskites and silicon solar cells, with tremendous impact on the swift deployment of renewable energy on a large scale.

Quasi-Zero Dimensional Halide Perovskite Derivates: Synthesis, Status, and Opportunity

In recent decades, many technological advances have been enabled by nanoscale phenomena, giving rise to the field of nanotechnology. In particular, unique optical and electronic phenomena occur on length scales less than 10 nanometres, which enable novel applications. Halide perovskites have been the focus of intense research on their optoelectronic properties and have demonstrated impressive performance in photovoltaic devices and later in other optoelectronic technologies, such as lasers and light-emitting diodes. The most studied crystalline form is the three-dimensional one, but, recently, the exploration of the low-dimensional derivatives has enabled new sub-classes of halide perovskite materials to emerge with distinct properties. In these materials, low-dimensional metal halide structures responsible for the electronic properties are separated and partially insulated from one another by the (typically organic) cations. Confinement occurs on a crystal lattice level, enabling bulk or thin-film materials that retain a degree of low-dimensional character. In particular, quasi-zero dimensional perovskite derivatives are proving to have distinct electronic, absorption, and photoluminescence properties. They are being explored for various technologies beyond photovoltaics (e.g. thermoelectrics, lasing, photodetectors, memristors, capacitors, LEDs). This review brings together the recent literature on these zero-dimensional materials in an interdisciplinary way that can spur applications for these compounds. The synthesis methods, the electrical, optical, and chemical properties, the advances in applications, and the challenges that need to be overcome as candidates for future electronic devices have been covered.