Interplay between Exciton and Free Carriers in Organolead Perovskite Films

Wang, Wei; Liu, Yu; Wang, Xiangyuan; Liu, Yang; Lv, Yanping; Wang, Shufeng; Wang, Kai; Shi, Yantao; Xiao, Lixin; Chen, Zhijian; Gong, Qihuang

doi:10.1038/s41598-017-15097-y

Cited by 8 publications

(17 citation statements)

References 30 publications

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“…Under high excitation intensities, the FC density is half‐power‐law to and the FE density is linear to the excitation intensity. [ 39 ] As such, FC density always exhibits a half‐power‐law correlation to FE density. In a time‐integrated PL mode, the PL intensity for both the FC and FE is linearly proportional to the initial charge density, which thus results in the relationship of I FC – I FE 1/2 .…”

Section: Resultsmentioning

confidence: 99%

Exciton Character and High‐Performance Stimulated Emission of Hybrid Lead Bromide Perovskite Polycrystalline Film

Shi

et al. 2020

Advanced Optical Materials

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optical communication, detecting, and photovoltaic applications, owing to their advantages of tunable bandgap, long car rier lifetime, and high light absorption. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] These advantages have arisen because of the distinctive semiconductor and photo physics properties that such materials possess, including ultrahigh bandedge density of states, [15] ultralow charge trap ping crosssection, [16] and low defect den sities. [17] Recent findings, including the ultraslow hot carrier cooling, [18,19] ultralong polarization memory, [20] giant spinorbit Rashba splitting, [21] and weak electronlattice coupling, [22] further increase mys tery of the perovskites. Underlying these alluring characteristics are intrinsic elec tronic states of the perovskite materials, while the electronic structure ultimately determines their photoelectric conversion mechanisms and performances. [23,24] As such, exploring electronic states of the hybrid perovskite pos sesses important implications for improving performance of current devices and expanding application horizons of these materials.Nonetheless, a clear understanding of the intrinsic elec tronic structure and chargecarrier characters of the perovskite remains lacking, and controversies on these properties have always been ongoing. These endless controversies arise because of the observed complicated photophysics characteristics and distinct scenarios proposed for interpreting them. For instance, the electronic origin for bandedge dual emission bands within both the single crystal and polycrystalline perovskites is one of the controversial focuses. [25][26][27][28][29][30][31][32] These dual emission bands pro vide important spectroscopic information for elucidating the fine structure of bandedge electronic states. Photon recycling provided a satisfied explanation for this phenomenon within the single crystal methylammonium lead bromide (MAPbBr 3 ). [25] Indirect band structure induced by a static or dynamical Rashba effect is another common interpretation [30][31][32] since a giant Rashba splitting within MAPbBr 3 was indeed observed using angular resolved photoelectron spectroscopy. [21] The indirect band structure scenario was also proposed to explain an unu sual temperature dependent secondorder radiative recombina tion velocity. [33] In contrast, an experimental result supporting the direct bandgap structure was observed recently. [34] Another controversial focus is on the charge character of perovskite. The bandedge emission of the bromide perovskite was once Electronic states of hybrid perovskites enable their exceptional optoelectronic applications. Herein, through heterojunction enhanced exciton dissociation and global tracing of multiple radiative electronic states across wide temperature regions, it has been found that excitons while not free carriers dominate the bandedge photoelectric properties of hybrid lead bromide perovskite (MAPbBr 3 ). MAPbBr 3 has exhibited two types of excitons with giant binding energies and superior phas...

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Section: Resultsmentioning

confidence: 99%

Exciton Character and High‐Performance Stimulated Emission of Hybrid Lead Bromide Perovskite Polycrystalline Film

Shi

et al. 2020

Advanced Optical Materials

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“…As we mentioned in former parts, the surface roughness, the small scale of the domain, and the a 1 -a 2 phase characteristics are the obstacles for direct observation in working layers [21,63]. Fortunately, we developed a convenient optical method to identify the broad existence of subgrain twin domains hidden in MAPbI 3 active layers [85].…”

Section: Optical Methods To Observe the Broad Existence Of Subgrain Twmentioning

confidence: 99%

“…A 1 and A 2 represent the decay rate of monomolecular and bimolecular recombination, A 3 is another decay rate that originated from exciton-carrier collision (ECC). At high excitation density, the fixed fluorescence intensity I(n) performs as power index 1 representing coexistence of exciton and free carriers without ECC, while power index 3/2 which implies the dominance of ECC behavior at perovskite thin films [85]. For freshly made perovskite films without heat annealing (or slightly heated for removing solvent), the exciton and free carriers co-existed and interconverted to each other dynamically as shown in Figure 10a with obvious power index 1 at high excitation density.…”

Section: Optical Methods To Observe the Broad Existence Of Subgrain Twmentioning

confidence: 99%

“…For freshly made perovskite films without heat annealing (or slightly heated for removing solvent), the exciton and free carriers co-existed and interconverted to each other dynamically as shown in Figure 10a with obvious power index 1 at high excitation density. For thin films experiencing adequate heat annealing, the collision-induced quenching of exciton and free carriers (ECC) happened as illustrated in Figure 10b with power index 3/2 at high excitation density [85]. Since the non-annealed and annealed film were all with tetragonal phase, there must be some intrinsic morphological change appearing.…”

Section: Optical Methods To Observe the Broad Existence Of Subgrain Twmentioning

confidence: 99%

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Twin Domains in Organometallic Halide Perovskite Thin-Films

Liu

et al. 2018

Crystals

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The perovskite is a class of material with crystalline structure similar to CaTiO 3. In recent years, the organic-inorganic hybrid metallic halide perovskite has been widely investigated as a promising material for a new generation photovoltaic device, whose power conversion efficiency (PCE) record reaches 22.7%. One of its underlying morphological characteristics is the twin domain within those sub-micron sized crystal grains in perovskite thin films. This is important for discussion since it could be the key for understanding the fundamental mechanism of the device's high performance, such as long diffusion distance and low recombination rate. This review aims to summarize studies on twin domains in perovskite thin films, in order to figure out its importance, guide the current studies on mechanism, and design new devices. Firstly, we introduce the research history and characteristics of widely known twin domains in inorganic perovskite BaTiO 3. We then focus on the impact of the domain structure emerging in hybrid metallic halide perovskite thin films, including the observation and discussion on ferroelectricity/ferroelasity. The theoretical analysis is also presented in this review. Finally, we present a spectroscopic method, which can reveal the generality of twin domains within perovskite thin films. We anticipate that this summary on the structural and physical properties of organometallic halide perovskite will help to understand and improve the high-performance of photovoltaic devices.

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“…Thus, we attribute the PL peaks of P 1 and P 2 to the FC recombination and exciton recombination, respectively. Recent reports suggest that both excitons and free carriers coexist in MAPbI 3 , presenting a significant emissive exciton–FC collision . The lower‐than‐expected power‐law exponent for P 1 in this study may be caused by probably energy transfer from P 1 to P 2 , or/and the transition from FCs to excitons.…”

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confidence: 45%

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

Chen

et al. 2018

Advanced Optical Materials

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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...

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Interplay between Exciton and Free Carriers in Organolead Perovskite Films

Cited by 8 publications

References 30 publications

Exciton Character and High‐Performance Stimulated Emission of Hybrid Lead Bromide Perovskite Polycrystalline Film

Exciton Character and High‐Performance Stimulated Emission of Hybrid Lead Bromide Perovskite Polycrystalline Film

Twin Domains in Organometallic Halide Perovskite Thin-Films

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

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