Search

Photon-induced trap deactivation is commonly observed in organometal halide perovskites. Trap deactivation is characterized by an obvious photoluminescence (PL) enhancement. In this work, the properties of traps in CH3NH3PbI3 perovskite films were studied based on the PL enhancement excited by lasers of different wavelengths (633 nm and 405 nm). Two types of electron traps were identified; one can be deactivated by both 633 nm and 405 nm illuminations, whereas the other one can only be deactivated by 405 nm illumination. The energy levels of both types of traps were beneath the conduction band minimum. The expressions of the PL enhancement kinetics due to the trap deactivations by lasers of different wavelengths were derived. The ratio of the constants of the radiative recombination rate and the initial capture rates for both traps was determined from the PL enhancement. The trap deactivation was a photon-related process rather than a photocarrier-related process, and the deactivation time was inversely proportional to the photon flux density. [ABSTRACT FROM AUTHOR]

We have studied the nanoscale changes in morphology and optical properties during annealing for bulk-heterojunction poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) composite film. Thermal atomic force microscopy was used to monitor the morphology evolution of the film in situ quantitatively, which showed a migration and aggregation of PCBM with increasing temperature. Scanning near-field microscopy was used to investigate the quantitative changes in absorption behavior of the film in nanoscale with increasing annealing time at 140 °C, which indicated that the extent of absorption of the film was increased with increasing annealing time. However, a large PCBM aggregate (1 μm) was formed after the film annealed at 140 °C for 1 h. The aggregate interrupted the bicontinous morphology of the film and further affected the absorption behavior in nanoscale. Furthermore, the refractive index and extinction coefficient of the films increased after annealed 30 min at 140 °C, but decreased after an extended annealing for 60 min. The increase in optical properties indicated the film achieving a highly ordered structure upon heating. The results suggested that an optimized annealing process was at 140 °C for 30 min. Finally, devices with different annealing times at 140 °C were fabricated and evaluated. The highest charge mobility and power conversion efficiency of the device were fabricated as suggested annealing conditions. The nanoscale monitoring of the P3HT/PCBM film has been found to be very useful to determine the optimized annealing conditions for high efficiency photovoltaic device. [ABSTRACT FROM AUTHOR]

It is demonstrated that magnetic periodic arrays can be easily fabricated from direct writing water developable La0.7Sr0.3MnO3 electron beam resist. Two unique features of our approach are (1) the patterned La0.7Sr0.3MnO3 resist film can be developed using nontoxic and environmentally friendly pure water and (2) either positive or negative patterns can be fabricated depending on the dosage of electron beam. The mechanism of the dual function characteristic of the resist was studied using Kelvin probe microscope. The surface potential of patterned La0.7Sr0.3MnO3 resist increases with increasing electron beam dosage due to the changes of resist composition. The formations of periodic magnetic arrays were confirmed by the studies of scanning electron microscope and magnetic force microscope. The magnetization of La0.7Sr0.3MnO3 can be enhanced by postsintering the sample at 900 °C after electron beam irradiation. We have therefore provided a one-step, simple, and convenient alternative technique for the fabrication of nanoscale magnetic patterns, which form the building blocks for the study of physical properties in periodic magnetic arrays. [ABSTRACT FROM AUTHOR]

Lead halide perovskite-structured solar cells (PSCs) have drawn great attention due to a rapid improvement in their photoelectric conversion efficiency in recent years. In this study, we have enhanced photovoltaic performance by using mesoscopic zinc-doped TiO2 (meso-Zn:TiO2) as the electron extraction layer. Zn:TiO2 nanoparticles (Zn:TiO2 NPs) with various zinc doping levels were synthesized by combining sol–gel and hydrothermal methods. The synthesized Zn:TiO2 NPs were used to fabricate electron extraction layers by a screen-printing method. We systematically investigated the surface morphology, crystal structure, contact angle, charge carrier dynamics, electron mobility, and electrical conductivity of various meso-Zn:TiO2. Furthermore, photo-assisted Kelvin probe force microscopy (KPFM) was used to analyze the surface potential of perovskite films coated with various meso-Zn:TiO2 to understand the electron extraction behavior under the illumination of light at various wavelengths. Moreover, the energy levels of various meso-Zn:TiO2 were estimated by ultraviolet photoelectron spectroscopy (UPS) and UV-vis absorption spectroscopy. We discovered that the 5.0 mol% meso-Zn:TiO2 exhibited the optimal band alignment with perovskite. Finally, the average power conversion efficiency (PCE) of PSCs with meso-Zn:TiO2 was enhanced from 13.1 to 16.8%, and such fabricated PSC yielded a champion PCE of 18.3%. [ABSTRACT FROM AUTHOR]

Various silver‐doped titanium dioxide (Ag‐TiO2) hole blocking layers are used to improve the organolead halide perovskite‐structured solar cells (PSCs) performances. In this work, a series of Ag‐TiO2 compact layers with various dopant levels are successfully synthesized, and they are used to fabricate PSCs. The silver doping effects on the morphology and physical properties of Ag‐TiO2 compact layers are studied using X‐ray diffractometer, UV‐visible spectroscopy, contact angle meter, scanning electron microscope, atomic force microscope, and time‐resolved photoluminescence spectroscopy. Furthermore, the photo‐assisted Kelvin probe force microscopy is used to monitor the surface potentials. With 1.0 mol% Ag‐TiO2 PSCs, the short‐circuit current density increases notably because of the lower electron–hole recombination, which increases the electron injection. After optimizing the synthesis conditions, the champion device based on 1.0 mol% Ag‐TiO2 exhibits a power conversion efficiency of 14.1% under AM 1.5 G irradiation (100 mW · cm−2). [ABSTRACT FROM AUTHOR]