Solution-processed hybrid organolead trihalide (MAPbX 3 ) perovskite solar cells (PSCs) have now achieved 20.1% certified power conversion efficiencies (1), following a rapid surge of development since perovskite based devices were first reported in 2009 (2). A key to the success of PSCs is the long diffusion length of charge carriers in the absorber perovskite layer (3). This parameter is expected to depend strongly on film crystallinity and morphology. Thermally evaporated MAPbI 3 films fabricated using a Cl --based metal salt precursor were reported to exhibit carrier diffusion lengths three times those of the best solution-processed materials, yet no measurable Cl -was incorporated in the final films, hinting at amajor but unclear mechanism in the control of crystallinity and morphology (4, 5). These observations suggest that there may be room to improve upon already remarkable PSC efficiencies via the optimization of three key parameters: charge carrier lifetime, mobility, and diffusion length.The quest for further improvements in these three figures of merit motivated our exploration of experimental strategies for the synthesis of large single-crystal MAPbX 3 perovskites that would exhibit phase purity and macroscopic (millimeter) dimensions. Unfortunately, previously published methods failed to produce single crystals with macroscopic dimensions large enough to enable electrode deposition and practical characterization of electrical properties (6). Past efforts based on cooling-induced crystallizationwere hindered by (i) the limited extent to which solubility could be influenced by controlling temperature, (ii) the complications arising from temperature-dependent phase transitions inMAPbX3, and(iii) the impact of convective currents (arising from thermal gradients in the growth solution) that disturb the ordered growth of the crystals.We hypothesized that a strategy using antisolvent vapor-assisted crystallization (AVC), in which an appropriate antisolvent is slowly diffused into a solution containing the crystal precursors, could lead to the growth of sizableMAPbX3 crystals of high quality (with crack-free, smooth surfaces,well-shaped borders, and clear bulk transparency). Prior attempts to grow hybrid perovskite crystals with AVC have fallen short of these qualities-a fact we tentatively attributed to the use of alcohols as antisolvents (7). Alcohols act as good solvents for the organic salt MAX (8) due to solventsolute hydrogen bond interactions; as a result, they can solvate MA+ during the ionic assembly of the crystal, potentially disrupting long-range lattice order.We instead implemented AVC (Fig. 1A) using a solvent with high solubility and moderate coordination for MAX and PbX 2 [N,Ndimethylformamide (DMF) or g-butyrolactone (GBA)] and an antisolvent in which both perovskite precursors are completely insoluble [dichloromethane (DCM)]. We reasoned that DCM, unlike alcohols, is an extremely poor solvent for both MAX and PbX 2 and lacks the ability to form hydrogen bonds, thus minimizing asymmetric i...

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.

Supporting Information Materials and MethodsChemicals and reagents. Lead bromide (≥ 98%), lead iodide (99.999% trace metal basis), DMF (anhydrous, 99.8%) and GBL (≥ 99%) were purchased from Sigma Aldrich. MABr, FABr and FAI were purchased from Dyesol Limited (Australia). All salts and solvents were used as received without any further purification. MAPbBr 3 , FAPbBr 3 and FAPbI 3 single crystals were grown by Inverse Temperature Crystallization (ITC) technique from 1 M solution of PbBr 2 /MABr in DMF, 1 M solution PbBr 2 /FABr in DMF:GBL (1:1 v/v) and 0.8 M solution of PbI 2 /FAI in GBL, respectively, as it was previously reported by Saidaminov et al. 1,2Powder X-ray diffraction was performed on a Bruker AXS D8 diffractometer using Cu-Kα radiation.

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.

Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells. Nature Materials.