Despite tremendous progress in optoelectronic devices using lead perovskite (CH3NH3(+)PbI3(-)), there has been a paucity of mechanistic information on how photoactive micron-sized crystals of lead perovskite grow from a mixture of a layered crystal of lead(II) iodide and methylammonium iodide mediated by a polar solvent, DMSO or DMF. We report here that the whole process of the lead perovskite synthesis consists of a series of equilibria driven by reversible solvent participation involving a polymeric strip of plumbate(II) oligomer as a key intermediate. A significant finding includes quick decomposition of perovskite crystal upon exposure to DMSO or DMF at room temperature, where the solvent molecules act as a base to remove acidic ammonium iodide from the perovskite crystal. This observation accounts for the difficulty in controlling perovskite solar cell fabrication. Overall, the polar solvent is indispensible first to degrade a 2-D sheet of crystals of lead(II) iodide into 1-D fibrous intermediates and then to promote Oswald ripening of perovskite crystals. The detailed chemical information provided here will help to rationalize the photovoltaic device studies that have so far remained empirical and to open a new venue to a developing field of microscale lead perovskite devices, as illustrated by fabrication of photovoltaic devices and photodetectors.

We fi rst describe the preparation of a fi lm of PVP-PV nanocrystals. A 4:1:1 molar mixture of dry crystalline methylammonium iodide (MAI), PbI 2 , and PbCl 2 , and x wt% of PVP ( x = 0, 3, 6; M w = 40 k) were dissolved in N , N -dimethylformamide (DMF) at 60 °C for 12 h and used as a precursor solution. While the value x was varied, the concentration of the precursors excluding PVP was kept at 25 wt%. We then spincoated the precursor solution on either glass/ITO or glass/ITO/ PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate)), followed by heating at 100 °C for 25 min and rapid cooling to room temperature under nitrogen. In accordance with a recent report, [ 26 ] the PV fi lm thus prepared contains 97.1% iodine atoms and only 2.9% Cl atoms, indicating that the chloride anion was largely extruded as MA + Cl − (see Figure S1, Supporting Information, Energy-dispersive X-ray spectroscopic (EDS) data). Thus, the composition of the active layer discussed below is denoted CH 3 NH 3 PbI 3x Cl x (PV), where x is a very small number. PVP ( M w = 40 k) is widely used for the stabilization of inorganic nanoparticles [ 27 ] and was found to be the best among several different types of polymers (e.g., polymethylmethacrylate, polyvinylpyridine).Next, we describe differential scanning calorimetry (DSC) analysis of PVP-PV fi lms prepared on glass/ITO. A thin fi lm for analysis was carefully scraped off from the glass/ITO/PVP-PV with a surgical blade (note that mechanical stress causes a phase change, as discussed below). The DSC data are shown in Figure S2 (Supporting Information), providing evidence for the persistence of a cubic lattice over 5-100 °C. The 0 wt% PVP-PV samples, upon cooling to 5 °C or to -50 °C as shown in Figure S2a,b (Supporting Information), underwent a CTT transition at 52 °C, and a reverse transition at 55 °C upon heating to 100 °C and cooling, respectively. These data conform to the standard behavior of lead PV. [ 28 ] By contrast, the 3 wt% PVP-PV sample in Figure S2c (Supporting Information) cooled from 100 to -50 °C showed no discernable peak, but showed a broad peak at 42 °C upon heating from -50 °C. When we performed the cooling/heating cycle between 100 and 5 °C, we did not observe any phase transition, indicating that the cubic phase persists between 5 and 100 °C, as supported by X-ray diffraction (XRD) analysis described below.We fi rst describe the surface morphology of glass/ITO/ PEDOT:PSS/PVP-PV. The atomic force microscopy (AFM) analysis ( Figure 2 a-c) gave us the surface roughness parameter (Rq, root mean square). The Rq value of the surface of 0 wt% PVP-PV was 14.55 nm, the value for 3.0 wt% PVP (Figure 2 b) was 3.11 nm, i.e., much smoother, and the value for 6 wt% was 2.91 nm (Figure 2 c). The scanning electron microscopic (SEM) images are consistent with the AFM roughness data (Figure 2 d-f).We next discuss a low-angle diffraction peak of out-of-plane XRD of glass/ITO/PEDOT:PSS fi lms, as well as high-angle peaks of a stack of fi lms carefully removed from the substrate (w...

The dramatic and distinctive color changes induced upon the addition of fluoride, chloride, or dihydrogen phosphate ions (A−) to solutions of calix[4]pyrroles bearing anthraquinone moieties attached through a conjugating ethyndiyl linker (see picture) in dichloromethane allow the presence of these anionic substrates to be determined by simple visual means.

The oxidized octaethyltetraphenylporphyrin (1, OETPP) and the corresponding newly prepared octaisobutyltetraphenylporphyrin (3, OisoBuTPP) could be isolated from the reaction of OETPPLi2 (or OisoBuTPPLi2) with SOCl2. The X-ray analysis and the characteristic UV-vis spectra of 1 and 3 revealed that these are the first examples of 16 pi nonaromatic porphyrins.