MAPbI3, one of the archetypical metal halide perovskites, is an exciting semiconductor for a variety of optoelectronic applications. The photoexcited charge-carrier diffusion and recombination are important metrics in optoelectronic devices. Defects in grain interiors and boundaries of MAPbI3 films cause significant nonradiative recombination energy losses. Besides defect impact, carrier diffusion and recombination anisotropy introduced by structural and electronic discrepancies related to the crystal orientation are vital topics. Here, large-sized MAPbI3 single crystals (SCs) were grown, with the (110), (112), (100), and (001) crystal planes simultaneously exposed through the adjusting ratios of PbI2 to methylammonium iodide (MAI). Such MAPbI3 SCs exhibit a weak n-type semiconductor character, and the Fermi levels of these planes were slightly different, causing a homophylic p–n junction at crystal ledges. Utilizing MAPbI3 SCs, the photoexcited carrier diffusion and recombination within the crystal planes and around the crystal ledges were investigated through time-resolved fluorescence microscope. It is revealed that both the (110) and (001) planes were facilitated to be exposed with more MAI in the growth solutions, and the photoluminescence (PL) of these planes manifesting a red-shift, longer carrier lifetime, and diffusion length compared with the (100) and (112) planes. A longer carrier diffusion length promoted photorecycling. However, excessive MAI-assisted grown MAPbI3 SCs could increase the radiative recombination. In addition, it revealed that the carrier excited within the (001) and (112) planes was inclined to diffuse toward each other and was favorable to be extracted out of the grain boundaries or crystal ledges.

Nevertheless, the inherent high trap density existed around the grain boundaries of PCF is ineluctable, [14][15][16] which restricts unobstructed carrier transport and boosts carrier recombination probability. Therefore, the performance enhancement of perovskite PCF has reached a bottleneck.Owing to its conspicuous crystallinity, high mobility, and low trap density, perovskite SCF within dozens of micrometers, is more attractive as light absorber for PDs than perovskite PCF. [17,18] Meanwhile, the larger area of perovskite crystal means a larger light receiving area. This makes large-area perovskite crystals are well received in the field of solar cells, integrated circuits, and light sensor arrays. [19][20][21] Unfortunately, due to the lack of immature technology for growing largesize thin SCF, reports about perovskite SCF PDs with ultra-fast response and high sensitivity remain scarce. Besides, the rotation hysteresis of organic components (FA, MA, etc) under an electric field and their instabilities against humidity and oxygen hinder the application of hybrid perovskite PDs with ultra-fast response. Fully inorganic cesium halide perovskites CsPbBr 3 (X = Br, I) demonstrate better stability and optoelectronic performances, and are therefore expected to obtain high stability and ultra-fast response optical communication devices. [22][23][24][25][26][27] Herein, we firstly report the growth of centimeter scale CsPbBr 3 SCFs with high quality and controllable thickness (40 µm) by an improved space-limited inverse temperature crystallization (ISLITC) procedure, in which the crystal growth process is controlled through variable heat areas. The MSM high-performance PD based on CsPbBr 3 SCF shows a fast response speed (500 kHz). Moreover, the use of our PD in an optical communication system is finally demonstrated. Results and DiscussionFigure 1a briefly shows the alterable heating area growth method of CsPbBr 3 SCF. Once stable nuclei are formed in a small heating region, the heating area is enlarged from 0.01 to 13 cm 2 to reduce the wafer growth rate and thus obtain high-quality and large-size wafers. To obtain large thin singleThe photodetector (PD) is the key component to realize efficient optoelectronic conversion signal in the visible light communication (VLC) system. The response speed directly determines the bandwidth of the whole system. Metal halide perovskite is a neotype of low-cost solution processing semiconductor, with strong optical absorption, low trap density, and high carrier mobility, thus has been widely explored in photoelectric detection applications. However, previously reported perovskite polycrystalline photodetectors exhibit limited response speed due to the existence of grain boundaries.Here, an improved confined space method is developed through adjusting the heating area to control nucleation, resulting in centimeter scale fully inorganic perovskite CsPbBr 3 thin single crystal films (SCFs) (<40 µm). The smooth surface and high crystallinity of CsPbBr 3 SCFs render admirable exciton lif...

FA1–x–y MA x Cs y PbI3–z Br z perovskites exhibit excellent stability and optoelectronic performances in solar cells. However, the detailed contributions of each component toward preventing decomposition and phase transition are not understood. Here, we link the contributions of each component to lattice stability and carrier transport from a single crystal perspective, which eliminates the interference of grain boundaries and amorphous perovskite. The exquisite long-term stable trigonal FA1–x–y MA x Cs y PbI3–zBrz SCs under 90% humidity proves that Br is indispensable, which shrinks the lattice and brings contributive distortions for both octahedron (Oh ) and lattice framework, consequently weakening the lattice strain against phase transition. The Br content should be controlled within 15% to avoid phase segregation. Less than 5% content of MA adjusts Oh distortion and promotes carrier transport, but excessive MA increases the extraction risk by H2O. Introduction of Cs (5%) assists Br in bringing sufficient distortion to maintain lattice stability, and exceeding 10% can lead to the phase segregation.

The isolated [PbBr 6 ] octahedra in the zero-dimensional (0-D) perovskite Cs 4 PbBr 6 crystal lattice trigger localized optical transitions, which exhibits extremely unique optical properties and brings controversial topics concerning its optical properties, particularly about its photoluminescence (PL) nature. Herein, we successfully grown a series of large-scale Cs 4 PbBr 6−m X m (X = Cl, I) single crystals (SCs) from Cs-rich solutions, partially replacing Br with Cl and I, taking advantage of superiorities from SCs to explore optical behavior and eliminate the mutual transformation distraction between Cs 4 PbBr 6 and CsPbBr 3 . No CsPbBr 3 is detected in our Cs 4 PbBr 6−m X m (X = Cl, I) large SCs, whereas they exhibit obvious PL phenomena. It is revealed that the Cs 4 PbBr 6 SC exhibits intense PL, and the replacements of Br with Cl and I can regularly alter the crystal lattice, optical absorption cutoffs, and PL positions and bring multiple PL peaks, among which one is attributed to the Br vacancy (V Br ) and another originates from crystal lattice distortions triggered by both halogen replacements. Therefore, we proposed that the PL nature of CsPbBr 3−m X m (X = Cl, I) SCs originates from crystal lattice distortions that can be induced by both halogen replacements and V Br . Severe local lattice distortion, for example, in Cs 4 PbBr 6 films and powders, definitely can induce Cs 4 PbBr 6−m X m to transform toward CsPbBr 3 and therefore enhance the PL yield.

Large-scale, high-quality MAPbBr3 SCFs with high carrier lifetime and carrier mobility are grown by the altering heating area assisted space confined method.