Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Francisco‐López, Adrián; Charles, Bethan; Alonso, M.; Garriga, M.; Weller, Mark T.; Goñi, A. R.

doi:10.1002/adom.202001969

Cited by 17 publications

(25 citation statements)

References 74 publications

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“…Taken together, the above evidence makes shallow defects and bound excitons strong contenders for the origin of X 2 : although detectable, its absorption is much lower than the 1s transition associated with X 1 . Furthermore, it coincidences energetically with shallow defects in PbI 2 (Figure S6, Supporting Information) as well as bound excitons in bulk perovskites, [ 38 ] and exhibits an activation energy similar to one attributed to shallow traps in diffusion experiments on PEA 2 PbI 4 single crystals. [ 39 ] Non‐linearities and irreversible changes of the PL intensity could easily be explained through the well‐known photoactivation of halide‐related defects.…”

Section: Resultsmentioning

confidence: 92%

Photophysics of Two‐Dimensional Perovskites—Learning from Metal Halide Substitution

Kahmann

Duim

Fang

et al. 2021

Adv Funct Materials

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2D perovskites offers a rich playing field to explore exciton physics and they possess a great potential for a variety of opto-electronic applications. Whilst their photophysics shows intricate interactions of excitons with the lattice, most reports have so far relied on single compound studies. With the exception of variations of the organic spacer cations, the effect of constituent substitution on the photophysics and the nature of emitting species, in particular, have remained largely under-explored. Here PEA 2 PbBr 4 , PEA 2 PbI 4 , and PEA 2 SnI 4 (where PEA stands for phenylethylammonoium) are studied through a variety of optical spectroscopy techniques to reveal a complex set of excitonic transitions at low temperature. Weak high-energy features are attributed to vibronic transitions breaking Kasha's, for which the responsible phonons cannot be accessed through simple Raman spectroscopy. Bright peaks at lower energy are due to two distinct electronic states, of which the upper is a convolution of the free exciton and a localized dark state and the lower is attributed to recombination involving shallow defects. This study offers deeper insights into the photophysics of 2D perovskites through compositional substitution and highlights critical limits to the communities' current understanding of processes in these compounds.

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Section: Resultsmentioning

confidence: 92%

Photophysics of Two‐Dimensional Perovskites—Learning from Metal Halide Substitution

Kahmann

Duim

Fang

et al. 2021

Adv Funct Materials

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“…Optical Mater. 2022, 10, 2101661 radiative decay mechanism, due to the reason that bound excitons interact with defects located to the impurities, [61] while no impurities are induced in our sample with high crystallinity. Combining the optical features of Rb 2 ZrCl 6 MCs (including broad emission spectrum, large Stokes shift, and long PL lifetime), we draw a conclusion that the PL emission of the as-obtained Rb 2 ZrCl 6 MCs is attributed to intrinsic STEs.…”

Section: Resultsmentioning

confidence: 92%

“…[ 60 ] While the PL spectrum of Rb 2 ZrCl 6 MCs is broad (approximately from 1.913 to 3.885 eV), the emission energy (2.795 eV) is much lower than the optical bandgap (3.895 eV, shown in Table 2), indicating that it does not conform to free excitons luminescence emission. Also, the PL emission of Rb 2 ZrCl 6 MCs cannot be attributed to bound excitons radiative decay mechanism, due to the reason that bound excitons interact with defects located to the impurities, [ 61 ] while no impurities are induced in our sample with high crystallinity. Combining the optical features of Rb 2 ZrCl 6 MCs (including broad emission spectrum, large Stokes shift, and long PL lifetime), we draw a conclusion that the PL emission of the as‐obtained Rb 2 ZrCl 6 MCs is attributed to intrinsic STEs.…”

Section: Resultsmentioning

confidence: 99%

Vacancy‐Ordered Double Perovskite Rb₂ZrCl₆₋_xBr_x: Facile Synthesis and Insight into Efficient Intrinsic Self‐Trapped Emission

Zheng

Chen

Xie

et al. 2021

Advanced Optical Materials

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X-ray imaging, [17][18][19] and light-emitting diodes (LEDs) due to their remarkable optoelectronic properties. [20][21][22][23][24][25][26] However, the lead toxicity and instability are serious issues toward their commercialization, [27,28] promoting the exploration of lead-free perovskite derivatives in the past several years. [29,30] One straightforward approach to replace Pb 2+ is to employ isovalent substitution of Sn 2+ and Ge 2+ owing to the same electronic configuration of ns 2 np 0 . [31] Regrettably, due to the high-energy-lying Sn 2+ 5s 2 and Ge 2+ 4s 2 states, Sn 2+ and Ge 2+ can be easily oxidized into Sn 4+ and Ge 4+ in ambient atmosphere, resulting in dominant defects of halogen vacancies and interstitial metals. [32][33][34] Another strategy to alleviate the toxicity of Pb 2+ is to adopt monovalent B + cations and trivalent B 3+ cations to form double perovskites with a general chemical formula of A 2 B + B 3+ X 6 , [35][36][37] such as Cs 2 AgBiX 6 , Cs 2 AgInX 6 , and Cs 2 AgSbX 6 , which suffer from low emission efficiencies ascribed to indirect bandgaps or direct forbidden bandgaps. [28,[38][39][40] Recently, vacancy-ordered perovskites have emerged as promising candidate for substitution of lead halide perovskites, owing to their advantages of high stability and high defect tolerance. The crystal unit of vacancy-ordered perovskites is very similar to that of the double perovskites, formed by doubling the conventional perovskite ABX 3 unit cell along all three crystallographic axes, subsequently removing every other B site cations. [41][42][43][44] Some efforts have been made to fabricate vacancy-ordered double perovskites in the past few years. For example, solvent-thermal method was adopted to fabricate Cs 2 ZrCl 6 (need 180 °C for 10 h), [31] and Cs 2 ZrX 6 (X = Cl, Br) nanocrystals were also got by using strict air-free Schlenk line technique. [45] Cs 2 TeI 6 film was fabricated by employing antisolvent method under a nitrogen atmosphere with controlled levels of H 2 O (<5 ppm). [46] Cs 2 SnI 6 nanocrystals were synthesized via hot-injection process at high temperature of 220 °C. [47] Obviously, challenges still lay ahead in terms of developing facile and low cost strategies under mild conditions to explore novel vacancy-ordered double perovskites.The grinding approach based on mechanochemistry as one of green and emerging efficient synthetic method which was Lead-free vacancy-ordered double perovskites with formula of A 2 M(IV)X 6 have become promising alternatives to lead halide perovskites. Herein, novel direct bandgap lead-free vacancy-ordered double perovskites Rb 2 ZrCl 6−x Br x (0 ≤ x ≤ 2) with highest photoluminescence quantum yield (PLQY) of 90% are synthesized by using a facile wet grinding approach. Experimental and theoretical analyses demonstrate that the bright emissions originate from the self-trapped excitons (STEs). Additionally, thermally activated delayed fluorescence (TADF) is observed in these perovskites, confirmed by temperature-dependent steadystate PL spectra and ...

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“…For example, increasing the size of the A‐site cation from Cs + to MA to FA narrows the bandgap due to decreased octahedral tilting. [ 8,9 ] Furthermore, cryogenic studies have demonstrated that the A‐site cation also impacts the temperature‐dependent optical [ 10–17 ] and structural properties. [ 14,15,18–24 ] Temperature‐dependent neutron/X‐ray diffraction and photoluminescence (PL) measurements on MAPbBr 3 revealed that the MA cation transformation from an ordered to a disordered state is correlated with an increased integrated PL intensity, and is also suggested to induce the orthorhombic to tetragonal phase transition.…”

Section: Introductionmentioning

confidence: 99%

Mixed Dimethylammonium/Methylammonium Lead Halide Perovskite Crystals for Improved Structural Stability and Enhanced Photodetection

et al. 2022

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The solvent acidolysis crystallization technique is utilized to grow mixed dimethylammonium/methylammonium lead tribromide (DMA/MAPbBr3) crystals reaching the highest dimethylammonium incorporation of 44% while maintaining the 3D cubic perovskite phase. These mixed perovskite crystals show suppression of the orthorhombic phase and a lower tetragonal‐to‐cubic phase‐transition temperature compared to MAPbBr3. A distinct behavior is observed in the temperature‐dependent photoluminescence properties of MAPbBr3 and mixed DMA/MAPbBr3 crystals due to the different organic cation dynamics governing the phase transition(s). Furthermore, lateral photodetectors based on these crystals show that, at room temperature, the mixed crystals possess higher detectivity compared to MAPbBr3 crystals caused by structural compression and reduced surface trap density. Remarkably, the mixed‐crystal devices exhibit large enhancement in their detectivity below the phase‐transition temperature (at 200 K), while for the MAPbBr3 devices only insignificant changes are observed. The high detectivity of the mixed crystals makes them attractive for visible‐light communication and for space applications. The results highlight the importance of the synthetic technique for compositional engineering of halide perovskites that governs their structural and optoelectronic properties.

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Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Cited by 17 publications

References 74 publications

Photophysics of Two‐Dimensional Perovskites—Learning from Metal Halide Substitution

Photophysics of Two‐Dimensional Perovskites—Learning from Metal Halide Substitution

Vacancy‐Ordered Double Perovskite Rb₂ZrCl₆₋_xBr_x: Facile Synthesis and Insight into Efficient Intrinsic Self‐Trapped Emission

Mixed Dimethylammonium/Methylammonium Lead Halide Perovskite Crystals for Improved Structural Stability and Enhanced Photodetection

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Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Cited by 17 publications

References 74 publications

Photophysics of Two‐Dimensional Perovskites—Learning from Metal Halide Substitution

Photophysics of Two‐Dimensional Perovskites—Learning from Metal Halide Substitution

Vacancy‐Ordered Double Perovskite Rb2ZrCl6−xBrx: Facile Synthesis and Insight into Efficient Intrinsic Self‐Trapped Emission

Mixed Dimethylammonium/Methylammonium Lead Halide Perovskite Crystals for Improved Structural Stability and Enhanced Photodetection

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Vacancy‐Ordered Double Perovskite Rb₂ZrCl₆₋_xBr_x: Facile Synthesis and Insight into Efficient Intrinsic Self‐Trapped Emission