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.

This highlight article gives an overview of the development of rylene diimide-based organic field-effect transistors and solar cells.

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...

Lead perovskite materials such as methylammonium triiodoplumbate(II) (CH3NH3PbI3, PV) are promising materials for printable solar cell (SC) applications. The preparation of PV involves a series of energetically costly cleavages of the μ-iodo bridges via conversion of a mixture of PbI2 (PI) and methylammonium iodide (CH3NH3I, MAI) in N,N-dimethylformamide (DMF) into a precursor solution containing a polymeric strip of a plumbate(II) dimer [(MA(+))2(PbI3(-))2·(DMF)2]m, which then produces a perovskite film with loss of DMF upon spin-coating and heating of the substrate. We report here that the PI-to-PV conversion and the PV crystal growth to micrometer size can be accelerated by a small amount of zwitterionic sulfamic acid (NH3SO3, SA) and that sulfamic acid facilitates electron transfer to a neighboring electron-accepting layer in an SC device. As a result, an SC device on indium tin oxide (ITO)/glass made of a 320 nm thick PV film using 0.7 wt % SA showed a higher short-circuit current, open-circuit voltage, and fill factor and hence a 22.5% higher power conversion efficiency of 16.02% compared with the device made without SA. The power conversion efficiency value was reproducible (±0.3% for 25 devices), and the device showed very small hysteresis. The device without any encapsulation showed a respectable longevity on a shelf under nitrogen under ambient light. A flexible device similarly fabricated on ITO/poly(ethylene naphthalate) showed an efficiency of 12.4%.

More than 50 years have passed since the first observation of graphitic cones in the pyrolysis of carbon. However, to date there has been no report in the literature on the synthesis of such carbon allotropes. Here we present the first synthesis of a carbon nanocone, which comprises a pentagon encircled by 30 hexagons, by means of a palladium-catalyzed cross-coupling reaction. In this synthetic approach, 15 C–C bonds were constructed from a cone-shaped aromatic scaffold, corannulene, and five naphthalene dicarboximide moieties through a cascade of [3 + 3] and [4 + 2] annulations. The conical geometry of the first synthetic carbon nanocone was confirmed by X-ray crystallography. The optical and electronic properties of this graphitic cone were elucidated by UV/vis and fluorescence spectroscopy and cyclic voltammetry.