We analyzed the crystallization process of the CH3NH3PbI3 perovskite by observing real-time X-ray diffraction immediately after combining a PbI2 thin film with a CH3NH3I solution. A detailed analysis of the transformation kinetics demonstrated the fractal diffusion of the CH3NH3I solution into the PbI2 film. Moreover, the perovskite crystal was found to be initially oriented based on the PbI2 crystal orientation but to gradually transition to a random orientation. The fluctuating characteristics of the crystallization process of perovskites, such as fractal penetration and orientational transformation, should be controlled to allow the fabrication of high-quality perovskite crystals. The characteristic reaction dynamics observed in this study should assist in establishing reproducible fabrication processes for perovskite solar cells.

We report the fabrication of high quality thin films for semiconducting organic donor-acceptor charge-transfer (CT) compounds, (diC8BTBT)(FnTCNQ) (diC8BTBT = 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene and FnTCNQ [n = 0,2,4] = fluorinated derivatives of 7,7,8,8,-tetracyanoquinodimethane), which have a high degree of layered crystallinity. Single-phase and uniaxially oriented polycrystalline thin films of the compounds were obtained by co-evaporation of the component donor and acceptor molecules. Organic thin-film transistors (OTFTs) fabricated with the compound films exhibited n-type field-effect characteristics, showing a mobility of 6.9 × 10−2 cm2/V s, an on/off ratio of 106, a sub-threshold swing of 0.8 V/dec, and an excellent stability in air. We discuss the suitability of strong intermolecular donor–acceptor interaction and the narrow CT gap nature in compounds for stable n-type OTFT operation.

Silicon nanocrystals (Si-ncs) with quantum confinement properties represent an attractive photovoltaic material. The ability to collect the photogenerated current through efficient electronic transport and exciton dissociation is a current challenge for the deployment of Si-nc based solar cells. We report here on prospective and cost-effective approaches to engineer the surface of electrochemically etched Si-ncs by laser fragmentation in ethanol and water. The properties of the engineered Si-ncs have been analyzed in detail by photoluminescence and absorption measurements together with Fourier transform infrared spectroscopy. To demonstrate the advantageous attributes of Si-nc surface engineering in liquid media, a few photovoltaic devices based on different architectures have been fabricated. First, anatase TiO2 nanotubes have been used as a host template for laser-fragmented Si-ncs to form inorganic-sensitized solar cell architectures. Second, we have produced bulk-heterojunction solar cells with a Si-nc/fullerene photoactive interface. This design has been further improved by functionalizing the Si-nc surface with water-soluble poly(3,4-ethylenedioxythiophene), i.e., PEDOT. All the devices produced here have been characterized with external quantum efficiency measurements, and in some cases the current−voltage characteristic has been also measured.

We demonstrate that nanosecond-pulsed laser chemistry in water leads to closely packed and stable luminescent assemblies of silicon nanocrystals (SiNCs) that can be electronically coupled with fullerenes (C60) without any additional surfactant or catalyst. We show that the fragmentation time in water determines the photoluminescence (PL) intensity (>40%) and redshifts the PL maxima (45 nm) of the SiNCs. Heterojunction solar cells made out of these laser-produced self-assemblies of SiNCs and C60 show photovoltaic action with increased quantum efficiency in the region where the absorption of SiNCs appears.

Photodisintegration cross sections were measured for deuterium with Laser-Compton scattering ␥ beams at seven energies near threshold. Combined with the preceding data, R(E)ϭN a v for the p(n,␥)D reaction is for the first time evaluated based on experimental data with 6% uncertainty in the energy region relevant to the big bang nucleosynthesis ͑BBN͒. The result confirms the theoretical evaluation on which the BBN in the precision era relies.