Efficient carrier multiplication in CsPbI3 perovskite nanocrystals

Weerd, Chris de; Gómez, Leyre; Capretti, Antonio; Lebrun, Delphine; Matsubara, Eiichi; Lin, Junhao; Ashida, Masaaki; Spoor, Frank C. M.; Siebbeles, Laurens D. A.; Houtepen, Arjan J.; Suenaga, Kazu; Fujiwara, Yoshihiro; Gregorkiewicz, T.

doi:10.1038/s41467-018-06721-0

Cited by 117 publications

(109 citation statements)

References 59 publications

(72 reference statements)

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“…For instance, Li et al demonstrated enhanced MEG with threshold down to 2.25 times of the bandgap and slope efficiency up to 75% in intermediate‐confined colloidal FAPbI 3 nanocrystals, and the efficient MEG was found to occur within 90 fs via inverse Auger process . Simultaneously, Weerd et al reported the observation of highly efficient (up to 98%) MEG or carrier multiplication in colloidal CsPbI 3 nanocrystals, with the threshold near the energy conservation limit of twice the bandgap . Such efficient MEG process observed in perovskite nanocrystals may lead to the realization of next generation of solar cells that can overcome the Shockley–Queisser limit.…”

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 98%

“…Many other studies also revealed the ultrafast behaviors of localized excitons, biexcitons, trions and multiple exciton generation in perovskites by transient techniques. He et al reported that the radiative recombination of the photogenerated species in solution‐processed methylammonium–lead–halide films was dominated by excitons weakly localized in band tail states, under the excitation level close to the working regime of solar cells, and such exciton localization effect was found to be general in several solution‐process perovskite films .…”

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

“…Makarov et al demonstrated that, similar to other types of nanocrystals, cesium–lead–halide perovskite QDs were prone to photocharging, leading to the formation of trions that decayed primarily via the Auger process on the time scale of ≈20–100 ps . More interestingly, since the recent observations of a hot‐phonon bottleneck effect existed in perovskites with slow hot‐carrier cooling dynamics, multiple exciton generation (MEG) process that competes with hot‐carrier cooling was able to be observed in perovskite nanocrystals with the property of slow hot‐carrier cooling due to the intrinsic phonon bottleneck . For instance, Li et al demonstrated enhanced MEG with threshold down to 2.25 times of the bandgap and slope efficiency up to 75% in intermediate‐confined colloidal FAPbI 3 nanocrystals, and the efficient MEG was found to occur within 90 fs via inverse Auger process .…”

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

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Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

2019

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their great success in photovoltaics (PVs), with a phenomenally rapid rise of the power conversion efficiency (PCE) from 3.8% [1] to over 23% [2,3] in the past few years. Such high PCE of perovskite solar cells has been ascribed to the ultralong carrier lifetimes, [4][5][6][7][8] long carrier diffusion lengths, [9][10][11][12][13][14] and the extraordinarily defect tolerance. [15][16][17] Following the success of perovskites in photovoltaics, research on light-emitting diodes (LEDs), [18,19] amplified spontaneous emission (ASE) or lasers, [20][21][22][23][24] and photodetectors [25][26][27][28][29] have also gained substantial interests. Meanwhile, the rapid progress of MHPs on various applications spurred a flurry of photophysical studies in order to understand the origin of the high performance of these devices, of which the nature of the photoexcitation species has been mostly debated. [5,22,30,31] Since the photoexcitation states near the bandgap affect the key processes such as charge transport and light emission of optoelectronic devices, there is no doubt that the investigation of electronic excitations near the optical band edge is crucial for MHPs. Such knowledge is essential not only for understanding the correlation between the fundamental photophysics and device performances, but also offering a guideline for their further applications with improved performances. Generally, there are two kinds of photoexcitations near the band edge for direct bandgap semiconductors: free carriers and excitons. Exciton binding energy that reflects the Coulomb interaction strength between photoexcited electrons and holes determines the balance of the populations between the two species. Typically, inorganic semiconductors are free-carrier materials with the exciton binding energies only in few meV at room temperature and their excited states being populated principally by free carriers. While organic semiconductors are excitonic materials with the exciton binding energies in hundreds of meV and thus excitons prevailing in the excited states. Whereas, MHPs that combine some merits of organic and inorganic semiconductors seem to stand for an exotic class of semiconductors between these two limiting cases, with the experimentally determined exciton binding energy varying in a wide range of 2 to more than 50 meV for the prototype perovskite MAPbI 3 . [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Such large variations of the exciton binding energies reported for MHPs give rise to a strongly debated question, that is, whether free carriers or excitons are generated upon photoexcitation? In other words, what is the nature of the photoexcitation species Metal halide perovskites (MHPs) have recently attracted great attention from the scientific community due to their excellent photovoltaic performance as well as their tremendous potential for other optoelectronic applications such as light-emitting diodes, lasers, and photodetectors. Despite the rapid progress in device applications, a solid unders...

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Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 98%

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

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Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

2019

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“…The cubic structure of CsPbI 3 also can be stabilized by the colloidal quantum dot (QD) method, because the enlarging surface energy inhibits the phase transition . In addition, on the basis of the multiple exciton generation effects, the narrow bandgap colloidal QDs will exceed the single‐junction Shockley–Queisser solar efficiency limit to achieve higher theoretical efficiency …”

Section: Introductionmentioning

confidence: 99%

Spray‐Coated Colloidal Perovskite Quantum Dot Films for Highly Efficient Solar Cells

Yuan

Wang

et al. 2019

Adv Funct Materials

118

137

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A fully automated spray-coated technology with ultrathin-film purification is exploited for the commercial large-scale solution-based processing of colloidal inorganic perovskite CsPbI 3 quantum dot (QD) films toward solar cells. This process is in the air outside the glove box. To further improve the performance of QD solar cells, the short-chain ligand of phenyltrimethylammonium bromide (PTABr) with a benzene group is introduced to partially substitute for the original long-chain ligands of the colloidal QD surface (namely PTABr-CsPbI 3 ). This process not only enhances the carrier charge mobility within the QD film due to shortening length between adjacent QDs, but also passivates the halide vacancy defects of QD by Br − from PTABr. The colloidal QD solar cells show a power conversion efficiency (PCE) of 11.2% with an open voltage of 1.11 V, a short current density of 14.4 mA cm −2 , and a fill factor of 0.70. Due to the hydrophobic surface chemistry of the PTABr-CsPbI 3 film, the solar cell can maintain 80% of the initial PCE in ambient conditions for one month without any encapsulation. Such a low-cost and efficient spraycoating technology also offers an avenue to the film fabrication of colloidal nanocrystals for electronic devices.with a large bandgap of 2.82 eV. [24,25] Many efforts have tried to partly replace I − with Br − to increase the stability of the black phase. [17,26,27] Unfortunately, the introduction of the bromine component enlarges the bandgap of the perovskite, correspondingly to harm the light-harvesting performance. The cubic structure of CsPbI 3 also can be stabilized by the colloidal quantum dot (QD) method, because the enlarging surface energy inhibits the phase transition. [28][29][30] In addition, on the basis of the multiple exciton generation effects, the narrow bandgap colloidal QDs will exceed the single-junction Shockley-Queisser solar efficiency limit to achieve higher theoretical efficiency. [31,32] Several efforts have built the devices with quite inspiring efficiency using the CsPbI 3 QD film as the active layer. [14,30,[33][34][35][36][37][38] However, the CsPbI 3 QDs are usually deposited to form the thin film by the spin-coating method. This method is an undesirable way to realize the scaled manufacture of the QD thin film because of the small deposition area. [39] To economize the cost of materials and realize scalable film deposition, the spray coating is emerging as a typical process for the fabrication of the thin films and has been used in the commercial paint coat technology. [32,39] However, the spray-coating process is hard to obtain high quality compact thin-film of colloidal QD due to long chain surface organic ligands of QD that weakens the adhesive force between QD and substrate. The surface ligands are obstructive to the formation of QD films and performance of the devices by hindering the charge transport. But the surface ligands are necessary to maintain monodisperse QDs and suppress their agglomeration. How to balance the surface ligands and the adhesive f...

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“… 22 The slow cooling rates are beneficial for MEG to occur, and investigations have reported on high efficiencies hereof in perovskite QDs. 23 , 24 …”

Section: Introductionmentioning

confidence: 99%

Direct Visualization and Determination of the Multiple Exciton Generation Rate

et al. 2020

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Multiple exciton generation (MEG) takes place in competition to other hot carrier cooling processes. While the determination of carrier cooling rates is well established, direct information on MEG dynamics has been lacking. Here, we present a methodology to obtain the MEG rate directly in the initial ultrafast transient absorption dynamics. This method is most effective to systems with slow carrier cooling rates. Perovskite quantum dots exhibit this property and are used to illustrate this approach. They show a delayed carrier concentration buildup following an excitation pulse above the MEG threshold energy, which is accompanied by a faster carrier relaxation, providing a direct evidence of the MEG process. Numerical modeling within a simple framework of two competing cooling mechanisms allows us to extract the MEG rate and carrier energy cooling rates for this material. The presented methodology could provide new insights in carrier generation physics and valuable information for MEG investigations.

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Efficient carrier multiplication in CsPbI3 perovskite nanocrystals

Cited by 117 publications

References 59 publications

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

Spray‐Coated Colloidal Perovskite Quantum Dot Films for Highly Efficient Solar Cells

Direct Visualization and Determination of the Multiple Exciton Generation Rate

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