Excitons versus free charges in organo-lead tri-halide perovskites

D’Innocenzo, Valerio; Grancini, Giulia; Alcocer, Marcelo J. P.; Kandada, Ajay Ram Srimath; Stranks, Samuel D.; Lee, Michael M.; Lanzani, Guglielmo; Snaith, Henry J.; Petrozza, Annamaria

doi:10.1038/ncomms4586

Cited by 1,585 publications

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“…The question as to which optically excited species may couple to the THz probe pulse, either excitons or free charge-carriers has been addressed several times in earlier reports. [ 17,18,[39][40][41][42] We note that for MAPbI 3 the sole response to the THz conductivity probe has already been shown to be that of a free-charge carrier density, as inferred from the Drude shape of the conductivity spectra. [ 17,18 ] Here we also report highly similar Drude conductivity spectra for FAPbBr 3 (see the Supporting Information), which suggests that excitonic effects are negligible at room temperature for these mixed I/Br materials.…”

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confidence: 71%

Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

et al. 2015

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by at least four orders of magnitude. [ 17,18 ] MAPbI 3 also appears to exhibit only shallow trap-levels and although the grain boundaries have recently been shown to induce nonradiative decay, [ 19 ] regions only a few tens of nm away from the grain boundaries appear to be unaffected. [ 20,21 ] Furthermore, low Urbach energies, which are extracted from near band edge optical absorption measurements and serve as a benchmark for crystalline phase disorder, indicate low disorder and sharp band edges for lead tri-halide perovskites (15-23 meV). [ 22,23 ] All of these properties contribute to high open-circuit voltages, long charge-carrier lifetimes, and micrometer diffusion lengths, which are crucial for planar-hetero junction photovoltaics. [ 1,24 ] Nonetheless, these parameters are also expected to depend on the infl uence of crystallization condition on perovskite morphology in fabricated fi lms. [ 25 ] A distinct benefi t of organic-inorganic perovskite materials (e.g., over silicon) is that their bandgap can be tuned relatively easily with chemical composition, allowing attractive coloration and multijunction or tandem cell designs. For example, changing the metal cation at the M site from Pb 2+ to the less toxic Sn 2+ to form CH 3 NH 3 SnI 3 shifts the optical bandgap from 1.55 to 1.3 eV into the range of the "ideal" single-junction solar cell bandgap between 1.1 and 1.4 eV. [ 26,27 ] However, stability issues arising from the oxidation of tin have so far prevented widespread use. Alternatively, tuning the size of the A site cation has been proven to change optical and electronic properties of the perovskite and to signifi cantly infl uence solar cell performance. [ 28 ] Replacing MA in MAPbI 3 by the larger cation formamidinium HC(NH 2 ) 2 + (FA) was found to decrease the bandgap from 1.57 to 1.48 eV, [29][30][31] yield long photoluminescence (PL) lifetimes, high PCEs, [ 28 ] and lower recombination and device hysteresis. [ 32 ] Highest PCEs of 20.1% have been reported [12][13][14] to date for solar cells based on FAPbI 3 making this an attractive system to explore. In addition, the gradual replacement of the MA cation by FA through the fi lm was shown to create a mixed cation-lead-iodide PSC allowing for energetic gradients. [ 33 ] However, mixing of the halide component in the perovskite offers the fi nest tuning of the optical properties of the perovskite fi lm. Here, the mixed organic lead iodide/bromide system has recently gained strong interest for application in PSCs. [ 11,28 ] By changing the ratio between bromide and iodide (at the X site anion), the bandgap can be tailored between 1.55 eV (MAPbI 3 ) and 2.3 eV (MAPbBr 3 ), which results in the coverage of much of the visible spectrum and paves the way for the development of tandem solar cells. [ 11 ] In addition to MAPb(Br y I 1-y ) 3 , its formamidinium relative FAPb(Br y I 1-y ) 3 has been explored. [ 28 ] Most fractional mixtures of FAPb(Br y I 1-y ) 3 were found to be crystalline, with the exception of the region between y = 0.3 and Recent year...

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Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

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“…The flawed films further led to the poorly performing devices 69. Moreover, due to the reaction kinetics between organic/inorganic halide and tin halide salts is faster than its lead analogs,19, 46, 156 the control of tin perovskite crystallization during the deposition process is more challenging. Therefore, developing novel preparation methods to achieve high‐quality tin perovskite film is of great importance to boost both efficiency and stability of Sn‐based PSCs.…”

Section: Lead‐free Halide Hybrid Perovskite and Related Absorbersmentioning

confidence: 99%

“…The unique electronic configuration of Pb 2+ endows 3D lead perovskites with excellent optoelectronic properties. For example, MAPbI 3 , the archetypal hybrid halide perovskite, possesses many ideal properties as a solar absorber: a direct bandgap ( E g ) of 1.53 eV,16 small exciton binding energies (37 or 45 meV),17, 18, 19 long charge carrier diffusion lengths over 3.5 µm,20, 21 and excellent charge carrier mobilities 22, 23, 24. Inherited all the merits of tribasic MAPbI 3 , the compositionally engineered polybasic 3D lead halide perovskite‐based PSCs exhibited a skyrocketing certified PCE from initial 14.9% to state‐of‐the‐art 22.1%25 within three years.…”

Section: Introductionmentioning

confidence: 99%

Lead‐Free Hybrid Perovskite Absorbers for Viable Application: Can We Eat the Cake and Have It too?

2017

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Many years since the booming of research on perovskite solar cells (PSCs), the hybrid perovskite materials developed for photovoltaic application form three main categories since 2009: (i) high‐performance unstable lead‐containing perovskites, (ii) low‐performance lead‐free perovskites, and (iii) moderate performance and stable lead‐containing perovskites. The search for alternative materials to replace lead leads to the second group of perovskite materials. To date, a number of these compounds have been synthesized and applied in photovoltaic devices. Here, lead‐free hybrid light absorbers used in PV devices are focused and their recent developments in related solar cell applications are reviewed comprehensively. In the first part, group 14 metals (Sn and Ge)‐based perovskites are introduced with more emphasis on the optimization of Sn‐based PSCs. Then concerns on halide hybrids of group 15 metals (Bi and Sb) are raised, which are mainly perovskite derivatives. At the same time, transition metal Cu‐based perovskites are also referred. In the end, an outlook is given on the design strategy of lead‐free halide hybrid absorbers for photovoltaic applications. It is believed that this timely review can represent our unique view of the field and shed some light on the direction of development of such promising materials.

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“…In these devices, perovskite layer with low exciton binding energy at room temperature acts as both light harvester and charge transport materials,94 rendering promising cost‐effective device architectures.…”

Section: Htm and Etm‐free Architecturesmentioning

confidence: 99%

High Performance Perovskite Solar Cells

et al. 2015

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Perovskite solar cells fabricated from organometal halide light harvesters have captured significant attention due to their tremendously low device costs as well as unprecedented rapid progress on power conversion efficiency (PCE). A certified PCE of 20.1% was achieved in late 2014 following the first study of long‐term stable all‐solid‐state perovskite solar cell with a PCE of 9.7% in 2012, showing their promising potential towards future cost‐effective and high performance solar cells. Here, notable achievements of primary device configuration involving perovskite layer, hole‐transporting materials (HTMs) and electron‐transporting materials (ETMs) are reviewed. Numerous strategies for enhancing photovoltaic parameters of perovskite solar cells, including morphology and crystallization control of perovskite layer, HTMs design and ETMs modifications are discussed in detail. In addition, perovskite solar cells outside of HTMs and ETMs are mentioned as well, providing guidelines for further simplification of device processing and hence cost reduction.

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Excitons versus free charges in organo-lead tri-halide perovskites

Cited by 1,585 publications

References 24 publications

Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

Charge‐Carrier Dynamics and Mobilities in Formamidinium Lead Mixed‐Halide Perovskites

Lead‐Free Hybrid Perovskite Absorbers for Viable Application: Can We Eat the Cake and Have It too?

High Performance Perovskite Solar Cells

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