Improved Power Conversion Efficiency and Stability of Perovskite Solar Cells Induced by Molecular Interaction with Poly(ionic liquid) Additives.

Ionic liquid (IL) additives proved to have a positive effect on the device efficiency and stability of perovskite solar cells. However, since ILs are small molecules and undergo Coulomb interactions, they can easily aggregate and evaporate over long times, which would cause instabilities during a long-term device operation. To overcome these problems, we polymerize ILs into macromolecules and incorporate them into perovskite films as well as into the corresponding solar cells. Both cations and anions of the used poly[1-(2-acryloylethyl)-3-methylimidazolium] bis (trifluoromethane) sulfonamides (PAEMI-TFSIs) are designed to coordinate with the Pb and I of PbI62- octahedra, respectively, which changes the crystallization behavior of the perovskite films. Importantly, the PAEMI-TFSI efficiently passivates electronic defects on the grain boundaries and thereby enhances the charge-carrier transport in the perovskite film. As a result, PAEMI-TFSI-modified MAPbI3 solar cells show a high power conversion efficiency of 22.4% and an excellent storage stability (92% of the initial efficiency remains after 1200 h operation in a nitrogen atmosphere for nonencapsulated devices).

SnO2 Passivation and Enhanced Perovskite Charge Extraction with a Benzylamine Hydrochloric Interlayer.

Perovskite solar cells (PSCs) have gained much attention because of their expressive power conversion efficiency (PCE) of up to 25.5%. A good contact and a well-aligned energy level at the buried interfaces between electron transport layers (ETLs) and perovskite films play an essential role in promoting charge-carrier collection and suppressing nonradiative recombination. Currently, low-temperature-processed SnO2 thin films are widely used as the ETLs to achieve efficient and stable planar PSCs. However, fabricating proper SnO2/perovskite interfaces with a good contact and a well-aligned energy level is necessary but implies a great challenge. Herein, we modify the SnO2 ETL using benzylamine hydrochloride (BH), which is expected to facilitate the energy level alignment and to enhance perovskite crystallization. Moreover, the BH interlayer is found to effectively reduce the trap-state density and thereby improve the charge-carrier extraction between the ETL and the perovskite layer. Consequently, the PSC with BH modification yields a higher PCE, a lower hysteresis, and better stability than the device without a BH interlayer. This study highlights the key role of molecule modification of ETLs in designing efficient and stable PSCs.

Ultraviolet lasing action in ZnO nanosheets.

We report room-temperature ultraviolet lasing action in large quantities of uniform multilayer ZnO nanosheets grown by a vapor-transport method via thermal evaporation of Zn powder. An excellent multimode lasing emission at a center wavelength of 390 nm with a mode linewidth less than 0.33 nm occurs above an excitation threshold of 8 mJ pulse(-1) cm(-2). The observed multimode lasing action may be attributed to microcavity effect and low concentration of defects in the nanosheets. We believe that the single-mode lasing emission can be obtained by growing completely uniform nanosheets. ZnO nanosheet is an attractive candidate as gain medium to realize ultraviolet semiconductor diode lasers.

Realization of blue, green, and white inverted microcavity top-emitting organic light-emitting devices based on the same emitting layer.

High efficiency blue, green, and white inverted microcavity top-emitting organic light-emitting devices based on blue emitter p-bis(p-N,N-diphenyl-amino-styryl) benzene-doped 2-methyl-9,10-di(2-naphthyl) anthracene as the emitting layer are demonstrated. The different colors can be well realized by simply changing the thickness of the hole-transporting layer, thus modifying the cavity length to obtain various resonance wavelengths. The comprehensive analysis on the emission mechanism is presented.

Amplified spontaneous emission from an Ag-backed red-fluorescent-dye-doped polymer film.

We demonstrate that the amplified spontaneous emission (ASE) in an Ag-backed red-fluorescent-dye-doped polymer film can be controlled by the effect of the film thickness. Optical losses associated with the metallic contacts necessary for charge injection, an obstacle to the development of an electrically pumped organic solid-state laser, may be possible to be reduced by increasing the gain medium layer thickness. The study of ASE characteristics of Ag-backed 4-(Dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB)-doped polystyrene (PS) films with different thicknesses shows that increasing the film thickness can reduce the influence of the Ag layer. The threshold, gain, and loss of the device with a thickness of 800 nm are comparable to those of a metal-free device. Our findings demonstrate that the Ag-backed DCJTB:PS film can still be a good organic gain medium material for the fabrication of solid-state lasers, when the thickness of the DCJTB:PS layer increases to an appropriate value.

Highly efficient inverted top-emitting organic light-emitting diodes using a lead monoxide electron injection layer.

By introducing an effective electron injection layer (EIL) material, i.e., lead monoxide (PbO), combined with the optical design in device structure, a high efficiency inverted top-emitting organic light-emitting diode (ITOLED) with saturated and quite stable colors for different viewing angles is demonstrated. The green ITOLED based on 10-(2-benzothiazolyl)-1, 1, 7, 7-tetramethyl-2, 3, 6, 7-tetrahydro-1H, 5H, 11H-[1] benzopyrano [6, 7, 8-ij] quinolizin-11-one exhibits a maximum current efficiency of 33.8 cd/A and a maximum power efficiency of 16.6 lm/W, accompanied by a nearly Lambertian distribution as well as hardly detectable color variation in the 140 degrees forward viewing cone. A detailed analysis on the role mechanism of PbO in electron injection demonstrates that the insertion of the PbO EIL significantly reduces operational voltage, thus greatly improving the device efficiency. More importantly, the optically optimized device structure by setting the resonant wavelength at the peak wavelength of the intrinsic emission of the emitter and adding an effective outcoupling layer further enhances the device efficiency, at the same time, also reduces the color shift with viewing angles, leading to the simultaneous optimization in efficiency and angular emission characteristics in the fabricated ITOLEDs.