Multipass inkjet printing and vacuum drying of MAPbI3 perovskite for better film thickness and crystal size control.

This paper reports on the impact of outdoor temperature variations on the performance of organo metal halide perovskite solar cells (PSCs). It shows that the open-circuit voltage ( V) of a PSC decreases linearly with increasing temperature. Interestingly, in contrast to these expected trends, the current density ( J) of PSCs is found to decline strongly below 20% of the initial value upon cycling the temperatures from 10 to 60 °C and back. This decline in the current density is driven by an increasing series resistance and is caused by the fast temperature variations as it is not apparent for solar cells exposed to constant temperatures of the same range. The effect is fully reversible when the devices are kept illuminated at an open circuit for several hours. Given these observations, an explanation that ascribes the temperature variation-induced performance decline to ion accumulation at the contacts of the solar cell because of temperature variation-induced changes of the built-in field of the PSC is proposed. The effect might be a major obstacle for perovskite photovoltaics because the devices exposed to real outdoor temperature profiles over 4 h showed a performance decline of >15% when operated at a maximum power point.

We report on the performance and stability of distributed feedback lasers based on the solution-processed methylammonium lead iodide perovskite (CH3NH3PbI3). The CH3NH3PbI3 layers are processed via solution-casting in ambient atmosphere onto nanoimprinted second order Bragg gratings. This way, we achieve highly polarized surface-emitted lasing at room temperature with a linewidth of less than 0.2 nm and a laser threshold of 120 kW/cm2. The lasing is stable; no change in the laser emission within 15 h of pulsed excitation with a repetition rate of 1 kHz (corresponding to >5 × 107 pulses) is observed, exceeding the stability achieved for solution processed organic semiconductor lasers. Furthermore, adjustment of the grating period allowed the lasing wavelength to be varied over the entire bandwidth of the amplified spontaneous emission (between 781 and 794 nm). The fabrication process of nanoimprinting followed by solution-casting of the gain material demonstrates that stable CH3NH3PbI3 lasers are compatible with scalable production technologies and offers a route towards electrically pumped diode architectures.

Intermetallic Cu 11 In 9 nanoparticles with diameters of 10−30 nm were prepared via a facile, easy-to-scale-up polyol-mediated synthesis. Citrate is used as surface-capping and guarantees for efficient stabilization of the Cu 11 In 9 nanoparticles against oxidation in suspension and of powder samples in contact to air. Moreover, the citrate-capping suppresses particle-to-particle agglomeration and allows to prepare high-quality suspensions and even to redisperse Cu 11 In 9 powder samples. The latter is essential to obtain stable inks with precise element composition that can be directly used for thin-film deposition via doctor blading. Based on as-deposited thin-films, high-quality CuInSe 2 (CIS) solar cells with power-conversion efficiencies up to 7% were produced by a simple and low-cost, vacuum-free selenization process without the need of additional reducing or sintering processes. Cu 11 In 9 nanoparticles and CIS thin-films as well as the completed solar cells were characterized by various independent analytical tools, including electron microscopy (SEM/STEM), DLS, FT-IR spectroscopy, EDX, XFA, XRD, and SIMS/SNMS.

Novel geometrical architectures of hybrid nanoparticle–protein complexes are generated by chemically synthesizing monodisperse metal nanoparticles in situ in the presence of a stable, stress‐related protein. The catalytic activity of the protein–particle hybrids is examined for the reduction of 4‐nitrophenol, providing future biofunctional nanoparticle labels for catalytic signal amplification in optical assays.

Charge-transfer (CT) states across organic heterojunctions play an important role in determining the efficiency of organic solar cells. These states can be the precursors of free charges or lead to geminate recombination losses. Here, we use time-resolved photoluminescence measurements to study charge-transfer states in a sequence of polythiophene:fullerene derivative blends with different mixing ratios, over the temperature range from 10 to 290 K, and after excitation with various photon energies. Our results show that (1) excess fullerene leads to a higher probability of CT state formation per absorbed photon and (2) the CT emission intensity is temperature-dependent whereas its emission lifetime is temperature-independent. Observation 1 cannot be explained solely by the increased fraction of excitations formed on fullerene-derivatives in the fullerene-rich blends, suggesting that disruption of the polymer packing at high fullerene loadings can negatively influence charge separation. Observation 2 suggests that relaxed, emissive CT states are formed in this system through a short-lived intermediate state whose separation into freecharges or relaxation into a bound CT state is temperature-dependent. Analysis of the temperature dependence suggests that there is no single activation energy for the CT*-to-CS transition, but rather a wide variety of different sites ranging in activation energy.

Formamidinium and guanidinium lead tri-iodide powders (FAPbI 3 and GUAPbI 3 respectively) were prepared by self-organization processes in solutions. The XRD analysis detected the formation, at room temperature, of a trigonal structure (α-FAPbI 3 , space group P3m1), of a (non-perovskitic) hexagonal structure (δ-FAPbI 3 , space group P63mc) for FAPbI 3 , and the presence of orthorhombic (space group Pnma) and hexagonal structures for GUAPbI 3 respectively. The morphological investigation revealed the growth of aggregated (α-FAPbI 3 phase) and stripe-like crystallites (GUAPbI 3) respectively. The infrared spectra (IR) confirmed the strong influence of additional C-N bonds on vibrational properties of GUA-containing system. Optical absorption measurements indicated that α-FAPbI 3 and GUAPbI 3 systems reveal direct energy band gaps of 1.42eV and 1.92eV respectively at room temperature. Photoluminescence measurements revealed emissions in the infra-red (IR) (for α-FAPbI 3) and visible (Vis) ranges (for GUAPbI 3). Films formation of GUAPbI 3 was demonstrated, and solar cells devices were fabricated with average power conversion of 0.3%.

We demonstrate that water filling has a significant, tube-diameter dependent effect on the effective mass density of individual single-walled carbon nanotubes suspended in aqueous suspension. On the basis of extensive molecular dynamics simulations of water-filled carbon nanotubes we have estimated the number density and properties of water molecules inside different types of nanotubes. As the tube diameter becomes comparable with the size of a water molecule, the number density of water molecules jumps discontinously. For tube diameters just above this threshold the water molecules organize into a single file. Shell-like arrangements are found for even larger radii. Buoyant densities are predicted to change accordingly.