Ahmed L. Abdelhady

Single crystals of methylammonium lead trihalide perovskites (MAPbX3; MA = CH3NH3(+), X = Br(-) or I(-)) have shown remarkably low trap density and charge transport properties; however, growth of such high-quality semiconductors is a time-consuming process. Here we present a rapid crystal growth process to obtain MAPbX3 single crystals, an order of magnitude faster than previous reports. The process is based on our observation of the substantial decrease of MAPbX3 solubility, in certain solvents, at elevated temperatures. The crystals can be both size- and shape-controlled by manipulating the different crystallization parameters. Despite the rapidity of the method, the grown crystals exhibit transport properties and trap densities comparable to the highest quality MAPbX3 reported to date. The phenomenon of inverse or retrograde solubility and its correlated inverse temperature crystallization strategy present a major step forward for advancing the field on perovskite crystallization.

Colloidal quantum dot research has led to significant advances in synthesis methods, in material and film processing techniques, and in characterization and optimization of optoelectronic properties. Studies of novel passivation strategies, including new or hybrid ligand systems, surface engineering, core/shell strategies, and self-healing surfaces, will reduce trap states, improve carrier transport, and reduce the extent of energy level pinning. Another route to improved electronic transport in quantum dot films will rely on densifying nanocrystal films through improved packing and, ideally ordering. Such films will eliminate diversity in path length and thus tortuosity in charge transport through the device. Significant studies have been performed on the electron-transporting component yet as the optoelectronic quality of the quantum dot solid improves, even greater enhancements will be required in both the electron- and hole-accepting layers to ensure optimal performance. Research will need to adjust existing systems or apply novel material solutions, while intensely studying the interfaces between the quantum dot film and electrodes to eliminate any potential losses. Finally, as single-junction quantum dot solar cells advance and improve, a renewed focus will be placed on multiple-junction integration, with the goal of creating high-efficiency devices through improved spectral utilization and minimal loss associated with photocarrier thermalization.

State-of-the-art perovskite solar cells with record efficiencies were achieved by replacing methylammonium (MA) with formamidinium (FA) in perovskite polycrystalline films. However, these films suffer from severe structural disorder and high density of traps; thus, the intrinsic properties of FA-based perovskites remain obscured. Here we report the detailed optical and electrical properties of FAPbX3 (where X = Br– and I–) single crystals. FAPbX3 crystals exhibited markedly enhanced transport compared not just to FAPbX3 polycrystalline films but also, surprisingly, to MAPbX3 single crystals. Particularly, FAPbBr3 crystals displayed a 5-fold longer carrier lifetime and 10-fold lower dark carrier concentration than those of MAPbBr3 single crystals. We report long carrier diffusion lengths—much longer than previously thought—of 6.6 μm for FAPbI3 and 19.0 μm for FAPbBr3 crystals, the latter being one of the longest reported values in perovskite materials. These findings are of great importance for future integrated applications of these perovskites.

Single crystals of hybrid perovskites have shown remarkably improved physical properties compared to their polycrystalline film counterparts, underscoring their importance in the further development of advanced semiconductor devices. Here we present a new method of growing sizable CH3NH3PbCl3 single crystals based on the retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy band structure, charge recombination, and transport properties of CH3NH3PbCl3 single crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility, and diffusion length comparable with the best quality crystals of methylammonium lead iodide or bromide perovskites reported so far. The high quality of the crystal along with its suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector, demonstrating its potential in optoelectronic applications.

Hybrid perovskites are promising semiconductors for optoelectronic applications. However, they suffer from morphological disorder that limits their optoelectronic properties and, ultimately, device performance. Recently, perovskite single crystals have been shown to overcome this problem and exhibit impressive improvements: low trap density, low intrinsic carrier concentration, high mobility, and long diffusion length that outperform perovskite-based thin films. These characteristics make the material ideal for realizing photodetection that is simultaneously fast and sensitive; unfortunately, these macroscopic single crystals cannot be grown on a planar substrate, curtailing their potential for optoelectronic integration. Here we produce large-area planar-integrated films made up of large perovskite single crystals. These crystalline films exhibit mobility and diffusion length comparable with those of single crystals. Using this technique, we produced a high-performance light detector showing high gain (above 10(4) electrons per photon) and high gain-bandwidth product (above 10(8) Hz) relative to other perovskite-based optical sensors.