Investigation on Charge Carrier Recombination of Hybrid Organic–Inorganic Perovskites Doped with Aggregation‐Induced Emission Luminogen under High Photon Flux Excitation

Abstract

recombination is still lacking-even for the most studied perovskite MAPbI 3 , for example, which could limit their further developments. Exciton effect plays a critical role in optoelectronic devices, such as photovoltaic cells, LEDs, and lasers. [11,12] The strength of electron-hole interaction is characterized by exciton binding energy. For photovoltaic cells, the exciton binding energy needs to be overcome for producing free electrons and holes to contribute to the photocurrent. Therefore, exciton binding energies below thermal energies at room temperature (RT) are highly desirable (<26 meV). [13] While for LEDs and lasers, a relative larger exciton binding energy is needed to obtain an efficient near-band-edge exciton emission at a wide range of temperatures (≈60 meV for semiconductor ZnO). [14] To date, great efforts have been made to determine the exciton binding energy of perovskite MAPbI 3 . [15][16][17][18][19] However, such an important physical parameter obtained from various experiments distributes in a wide range from 2 to 55 meV, which is a disadvantage of an accurate understanding of the photophysical properties of perovskites and their further applications.Along with the exciton binding energy, carrier recombination is another important issue in semiconductors. [20] Previous reports focused on this question that whether free carriers (FCs) or excitons are the dominant recombination specie in perovskites. Both FC recombination [5,16,21] and exciton recombination [22][23][24] were attributed to the RT photoluminescence (PL) of MAPbI 3 . Further investigations indicate the recombination behavior in perovskites has a close relation with the excitation intensity. [15,19,25,26] Moreover, several reports found the PL intensity shows square dependence on the excitation intensity, suggesting the FC recombination is dominant in PL processes. [19,26] However, He et al. [27] have argued that when a relatively high excitation level (photocarrier density (n 0 ) > 10 15 cm −3 ) is applied, the exciton binding energy decreases due to the screening effect of the large amount of photogenerated FCs. They also demonstrated that under an excitation level close to the working regime of solar cells (≈5 × 10 14 cm −3 ), the PL A typical aggregation-induced emission luminogen (AIE-gen) is introduced into perovskite CH 3 NH 3 PbI 3 and the material and photophysical properties of hybrid films are investigated with absorption, X-ray diffraction, and steadystate photoluminescence (PL) characterization. When excited by a high photon flux (4.08 × 10 22 cm −2 s −1 ) laser beam (3.82 eV) at room temperature, the CH 3 NH 3 PbI 3 polycrystalline thin films exhibit dual emission locating at 1.64 eV (P 1 ) and 1.59 eV (P 2 ). The two PL peaks are attributed to free carrier (FC) recombination and exciton recombination, respectively. Additionally, an introduction of AIE-gen changes the peak value ratio of P 1 :P 2 , indicating the radiative recombination ratio of FCs versus excitons in perovskite films can be tuned with this method. S...

Will organic–inorganic hybrid halide lead perovskites be eliminated from optoelectronic applications?

“…The formation of metal halide perovskite depends on three factors: (1) the charge neutrality between the anions and cations, (2) the stability of the BX 6 octahedron predicted by the octahedral factor μ , and (3) the ionic radii of A, B and X are in accordance with the requirements of the Goldschmidt tolerance factor t. 9 The octahedral factor μ , which is the ratio of the radius of the B-site cation ( r B ) and the halide counter ion ( r X ), can be used to estimate the thermal stability of the BX 6 octahedra ( eqn (6) ). The binding of the B-site cation is determined by the ion size limitations defined by the X 6 octahedra.…”

“…Also for a t greater than 1, the A cation is too large to form a perovskite structure, where a hexagonal structure will be formed instead of layers that, which includes face-sharing octahedra. 9,41–45 …”

“… 7 This outstanding performance can be attributed to the characteristics of halide perovskites with a high bipolar charge carrier mobility (around 0.6 cm 2 V −1 s −1 ), 8 balanced electron and hole transport, long carrier diffusion length, high absorption coefficient and direct and adjustable band gap. 9 …”

When Aggregation‐Induced Emission Meets Perovskites: Efficient Defect‐Passivation and Charge‐Transfer for Ambient Fabrication of Perovskite Solar Cells

“…In 2016, Chen et al introduced a typical AIE-gens into CH 3 NH 3 PbI 3 thin film and tuned the free carrier recombination and exciton recombination behavior of photogenerated carriers in perovskite films. [19] In 2017, Huang et al developed a light-harvesting and three-dimensional AIE molecule as a light-capturer, grain-boundary filler and an electron-donor for perovskite hybrid film, improving the crystallinity of perovskite film and enhancing the PCE of PSCs. [20] Thereby, incorporation of AIE materials into perovskite is a feasible method to improve the quality of perovskite film as well as the performance of PSCs.…”

Vanadium-Catalyzed Synthesis of Geometrically Defined Acyclic Tri- and Tetrasubstituted Olefins from Propargyl Alcohols

“…In addition to serving as a valuable building block for a wide variety of asymmetric transformations, the geometrically defined tetrasubstituted acyclic olefin motif is found in natural products and commercialized pharmaceuticals, and is of interest in materials science . Within this class of compounds, tetrasubstituted vinyl halides are of particular interest due to their versatility as substrates for metal-catalyzed cross-coupling reactions, allowing for the rapid formation of libraries of tetrasubstituted all-carbon olefins.…”