ABSTRACT
We report the CsPbI3 random lasing at room temperature fabricated by a chemical deposition method. The CsPbI3 thin films with high crystalline quality have intense PL emission and easily achieve the lasing behavior with the Q-factor value over 7000. The lasing behavior of CsPbI3 thin films can be classified as random lasing by measuring lasing spectra at different collective angles. The fast Fourier transform analysis of the lasing spectra is employed to determine the effective cavity length. Most important of all, the lasing stability investigation shows the prolonged lasing stability over 4.8 X 105 laser shots in air.
ABSTRACT
The development of hole-transport layers (HTLs) that elevate charge extraction, improve perovskite crystallinity, and decrease interfacial recombination is extremely important for enhancing the performance of inverted perovskite solar cells (PSCs). In this work, the nanoporous nickel oxide (NiO x ) layer as well as NiO x thin film was prepared via chemical bath deposition as the HTL. The sponge-like structure of the nanoporous NiO x helps to grow a pinhole-free perovskite film with a larger grain size compared to the NiO x thin film. The downshifted valence band of the nanoporous NiO x HTL can improve hole extraction from the perovskite absorbing layer. The device based on the nanoporous NiO x layer showed the highest efficiency of 13.43% and negligible hysteresis that was better than the one using the NiO x thin film as the HTL. Moreover, the PSCs sustained 80% of their initial efficiency after 50 days of storage. This study provides a powerful strategy to design PSCs with high efficiency and long-term stability for future production.
ABSTRACT
Two new phosphine ligands, diphenylmethylphosphine (DPMP) and triphenylphosphine (TPP), were introduced onto cesium lead bromoiodide nanocrystals (CsPbBrI2 NCs) to improve air stability in the ambient atmosphere. Incorporating DPMP or TPP ligands can also enhance film-forming and optoelectronic properties of the CsPbBrI2 NCs. The results reveal that DPMP is a better ligand to stabilize the emission of CsPbBrI2 NCs than TPP after storage for 21 days. The increased carrier lifetime and photoluminescence quantum yield (PLQY) of perovskite NCs are due to the surface passivation by DPMP or TPP ligands, which reduces nonradiative recombination at the trap sites. The DPMP and TPP-treated CsPbBrI2 NCs were successfully utilized as red emitters for fabricating perovskite light-emitting diodes with enhanced performance and prolonged device lifetime relative to the pristine one.
ABSTRACT
We realized a single-mode laser with an ultra-high quality factor in individual cesium lead bromide (CsPbBr3) perovskite micro-hemispheres fabricated by chemical vapor deposition. A series of lasing property analysis based on cavity size was reported under this material system. Due to good optical confinement capability of the whispering gallery resonant cavity and high optical gain of CsPbBr3 perovskite micro-hemispheres, single-mode lasing behavior was achieved with an ultra-high quality factor as large as 11,460 at room temperature. To study in detail the physical effects between lasing threshold and cavity, a set of cavity size dependence photoluminescence analyses were performed. We found that the lasing threshold increases while the cavity size decreases. Time-resolved PL analysis was conducted to confirm the relation between cavity size and lasing threshold. The larger cavity stands for longer PL lifetime and indicates easier-to-achieve carrier population inversion. Strong Purcell enhancement could be further investigated by the spontaneous emission coupling factor ß and internal quantum efficiency as a function of cavity size. A high ß-factor of 0.37 could be obtained from a 2.2 µm diameter hemisphere microcavity and a high Purcell factor of 14 in a 1.9 µm diameter hemisphere microcavity showing strong Purcell enhancement effect in our system.
ABSTRACT
Thermal photoluminescence (PL) quenching is fundamentally important for perovskite optoelectronic applications. Herein, we investigated PL characteristics of CsSnBr3 microsquares and micropyramids synthesized by chemical vapor deposition (CVD) and their PL quenching behavior at high temperature. These microstructures have favorable PL performances in ambient atmosphere. Under two-photon excitation, we observed whispering gallery modes (WGMs) in microsquares and amplified spontaneous emission (ASE) in micropyramids. Reversible PL losses due to thermal effect were observed for both samples. Monotonic blue shifts in PL emission upon temperature increase suggest a band gap widening associated with an emphanisis effect. Temperature-dependent spectral line width analysis reveals that a line width broadening is attributed to the dominant electron-longitudinal optical phonon interaction. The estimated activation energy of thermally assisted nonradiative recombination for CsSnBr3 microsquares and micropyramids is over 310 meV by the Arrhenius equation, which is higher than CsPbBr3. These results prove that CsSnBr3 exhibits better thermal stability than Pb-based perovskites.