Phase State Influence on Photoluminescence of MAPb(BrxI1−x)3 Perovskites towards Optimized Photonics Applications

Perovskite halide has many advantages that attracted the attention of researchers in the last years, but many challenges prevent the use of halide perovskites in different applications. One of these challenges is the low thermal stability resulting in phase transitions with temperatures. Here, the photoluminescence (PL) characteristics and related phase transitions of different CH3NH3Pb(BrxI1−x)3 (MA(BrxI1−x)3)3 perovskites structures have been investigated under a wide temperature range. The work that has been conducted demonstrates that under temperature, the exciton behavior of the halide anions, I and Br, has a considerable impact on structural phases and the fluorescence process. The obtained results for the temperature dependence of PL for MAPb(BrxI1−x)3 showed a wide range of emission wavelengths, between 500–800 nm with a decrease in PL intensity with increasing temperature. In addition, the ratio of both bromine and iodine in MAPb(BrxI1−x)3 affects the range of phase transition temperatures, where at x = 0.00, 0.25, and 0.50 the first transition occurs below room temperature (orthorhombic to tetragonal) phase and the other occurs above room temperature (tetragonal to cubic) phase. Furthermore, increasing the proportion of bromine causes all the transitions to occur below room temperature. The presented findings suggest a suitable halide component under a temperature-controlled phase transformation to benefit these materials in photonics devices

Surface Passivation for Promotes Bi-Excitonic Amplified Spontaneous Emission in CsPb(Br/Cl)₃ Perovskite at Room Temperature

Perovskite-type lead halides exhibit promising performances in optoelectronic applications, for which lasers are one of the most promising applications. Although the bulk structure has some advantages, perovskite has additional advantages at the nanoscale owing to its high crystallinity given by a lower trap density. Although the nanoscale can produce efficient light emission, its comparatively poor chemical and colloidal stability limits further development of devices based on this material. Nevertheless, bulk perovskites are promising as optical amplifiers. There has been some developmental progress in the study of optical response and amplified spontaneous emission (ASE) as a benchmark for perovskite bulk phase laser applications. Therefore, to achieve high photoluminescence quantum yields (PLQYs) and large optical gains, material development is essential. One of the aspects in which these goals can be achieved is the incorporation of a bulk structure of high-quality crystallization films based on inorganic perovskite, such as cesium lead halide (CsPb(Br/Cl)3), in polymethyl methacrylate (PMMA) polymer and encapsulation with the optimal thickness of the polymer to achieve complete surface coverage, prevent degradation, surface states, and surface defects, and suppress emission at depth. Sequential evaporation of the perovskite precursors using a single-source thermal evaporation technique (TET) effectively deposited two layers. The PL and ASEs of the bare and modified films with a thickness of 400 nm PMMA were demonstrated. The encapsulation layer maintained the quantum yield of the perovskite layer in the air for more than two years while providing added optical gain compared to the bare film. Under a picosecond pulse laser, the PL wavelength of single excitons and ASE wavelength associated with the stimulated decay of bi-excitons were achieved. The two ASE bands were highly correlated and competed with each other; they were classified as exciton and bi-exciton recombination, respectively. According to the ASE results, bi-exciton emission could be observed in an ultrastable CsPb(Br/Cl)3 film modified by PMMA with a very low excitation energy density of 110 µJ/cm2. Compared with the bare film, the ASE threshold was lowered by approximately 5%. A bi-exciton has a binding energy (26.78 meV) smaller than the binding energy of the exciton (70.20 meV)

Phase State Influence on Photoluminescence of MAPb(Br_xI_1−x)₃ Perovskites towards Optimized Photonics Applications

Perovskite halide has many advantages that attracted the attention of researchers in the last years, but many challenges prevent the use of halide perovskites in different applications. One of these challenges is the low thermal stability resulting in phase transitions with temperatures. Here, the photoluminescence (PL) characteristics and related phase transitions of different CH3NH3Pb(BrxI1−x)3 (MA(BrxI1−x)3)3 perovskites structures have been investigated under a wide temperature range. The work that has been conducted demonstrates that under temperature, the exciton behavior of the halide anions, I and Br, has a considerable impact on structural phases and the fluorescence process. The obtained results for the temperature dependence of PL for MAPb(BrxI1−x)3 showed a wide range of emission wavelengths, between 500–800 nm with a decrease in PL intensity with increasing temperature. In addition, the ratio of both bromine and iodine in MAPb(BrxI1−x)3 affects the range of phase transition temperatures, where at x = 0.00, 0.25, and 0.50 the first transition occurs below room temperature (orthorhombic to tetragonal) phase and the other occurs above room temperature (tetragonal to cubic) phase. Furthermore, increasing the proportion of bromine causes all the transitions to occur below room temperature. The presented findings suggest a suitable halide component under a temperature-controlled phase transformation to benefit these materials in photonics devices