Enhanced Incorporation of Guanidinium in Formamidinium‐Based Perovskites for Efficient and Stable Photovoltaics: The Role of Cs and Br

Zhou, Yang; Xue, Haibo; Jia, Yong; Brocks, G.; Tao, Shuxia; Zhao, Ni

doi:10.1002/adfm.201905739

Cited by 47 publications

(56 citation statements)

References 33 publications

(41 reference statements)

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“…In addition, Figure S2 (Supporting Information) shows the XRD and optical absorption spectra of the GA‐CsRb films modifies with GABr. The smaller angle shift with increasing GABr concentration reveal a gradual expansion of the crystal unit, indicating partial incorporation of the larger GA cation . The additional diffraction peaks (6.02°, 11.9°, and 28.2°) and emerging absorption transition at 540 nm (Figure S2c, Supporting Information) indicate that excess GABr tends to induce the formation of 2D GA 2 PbI 4 perovskite at the surface of the CsRb film as suggested by the grazing incidence X‐ray diffraction (GIXRD) results (Figure S2d, Supporting Information) .…”

Section: Resultsmentioning

confidence: 82%

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs_{(1 − x)}Rb_xPbI₂Br Inorganic Perovskite Solar Cells

Zhang

Xiong

et al. 2020

Solar RRL

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Inorganic CsPbI2Br perovskite has gained growing attention due to its potential for improving device performance and stability. However, the notorious phase transition from the photoactive to photoinctive phase in ambient atmosphere hinders its further development. Herein, air‐stable rubidium (Rb)‐incorporated Cs(1 − x)RbxPbI2Br perovskite with guanidinium bromide (GABr) post‐treatment is demonstrated. The incorporation of smaller monovalent Rb cation contributes to a contraction of the perovskite crystal, leading to an improvement in structure stability. In addition, GABr modification induces a 2D/3D heterostructure perovskite with high crystallinity, appropriate surface morphology, favorable electronic properties, and significantly reduced trap‐state density. Consequently, the fabricated perovskite solar cells deliver a power conversion efficiency (PCE) of 15.6%, which is much higher than the 12.9% reported for reference CsPbI2Br‐based devices. Meanwhile, the significantly enhanced long‐term (88% of initial PCE after 60 days), thermal (76% of initial PCE after 30 days) as well as light soaking (90% of initial PCE after 300 min) stability in ambient atmosphere is demonstrated.

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Section: Resultsmentioning

confidence: 82%

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs_{(1 − x)}Rb_xPbI₂Br Inorganic Perovskite Solar Cells

Zhang

Xiong

et al. 2020

Solar RRL

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“…The increased Coulomb interactions upon the incorporation of Cs + and Rb + is expected to increase the formation energy of iodide vacancies, effectively suppressing the creation and diffusion of the halide defects. [ 40,41 ] Using Rb‐modified perovskite as an example, we found an increase of about 200 meV in the defect formation energy of one of the iodide vacancies, which exhibits about 3% increase in net charge when sits near Rb. Considering the average increase in the net charge is about 4.6% (for Cs) or 5.9% (for Rb), we infer that the formation energies of other I vacancies near Rb or Cs would increase in a similar magnitude, i.e., within a few hundreds meV.…”

Section: Figurementioning

confidence: 98%

Stabilizing Perovskite Light‐Emitting Diodes by Incorporation of Binary Alkali Cations

Song

Jia

et al. 2020

Advanced Materials

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high-performance LEDs due to high photoluminescence (PL) quantum efficiency, narrow emission linewidth (i.e., high color purity), and low density of sub-gap electronic trap states. [6][7][8][9] Significant breakthroughs have been achieved in perovskite LEDs (PeLEDs) in the past 5 years, with the external quantum efficiency (EQE) boosted from 0.76% in 2014 to over 21% recently, [1,10,11] comparable to the stateof-the-art performance of organic LEDs (OLEDs). [12] Nevertheless, despite rapid development of electroluminescence (EL) efficiency, the commercialization of PeLEDs is still challenging due to the poor device stability, [13] which mainly stems from degradation of perovskite materials upon air exposure or electrical bias. As demonstrated in perovskite-based photovoltaic (PV) devices, migration of mobile ions under electrical bias stress causes destruction of the perovskite lattices and infiltration of mobile ions into adjacent layers. [14,15] In PeLEDs, a higher electricfield is present and may aggravate the ion migration issue. In particular, in contrast to the thick perovskite absorber layer in PV devices, the perovskite light-emitting layer in PeLEDs is much thinner (typically a few tens of nanometers) as required for spatial confinement of charge carriers and efficient radiative recombination. [1] Therefore, mobile ions in the thin perovskite layer would be The poor stability of perovskite light-emitting diodes (PeLEDs) is a key bottleneck that hinders commercialization of this technology. Here, the degradation process of formamidinium lead iodide (FAPbI 3 )-based PeLEDs is carefully investigated and the device stability is improved through binary-alkalication incorporation. Using time-of-flight secondary-ion mass spectrometry, it is found that the degradation of FAPbI 3 -based PeLEDs during operation is directly associated with ion migration, and incorporation of binary alkali cations, i.e., Cs+ and Rb + , in FAPbI 3 can suppress ion migration and significantly enhance the lifetime of PeLEDs. Combining experimental and theoretical approaches, it is further revealed that Cs + and Rb + ions stabilize the perovskite films by locating at different lattice positions, with Cs + ions present relatively uniformly throughout the bulk perovskite, while Rb + ions are found preferentially on the surface and grain boundaries. Further chemical bonding analysis shows that both Cs + and Rb + ions raise the net atomic charge of the surrounding I anions, leading to stronger Coulomb interactions between the cations and the inorganic framework. As a result, the Cs + -Rb + -incorporated PeLEDs exhibit an external quantum efficiency of 15.84%, the highest among alkali cation-incorporated FAPbI 3 devices. More importantly, the PeLEDs show significantly enhanced operation stability, achieving a half-lifetime over 3600 min.In recent years, solution-processed metal halide perovskites have attracted tremendous interests in the scientific community including the field of light-emitting diodes (LEDs). [1][2][3][4][5] Besides low fab...

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“…Regarding the concentration of GA + , it is calculated with the XRD peak shift in Figure S12 in the Supporting Information. [ 37 ] As summarized in Table S2 in the Supporting Information, the ratio of GA + in the film is ≈6.47% when the concentration of GAI in the IPA solution is 8 mg mL −1 . Therefore, we have used a close value of

x = \frac{1}{16}

(6.25%) to simulate the experimental concentrations of Br − , Cs + , and GA + .…”

Section: Figurementioning

confidence: 99%

“…The remnant PbI 2 peak in the perovskite films is eliminated with a higher Cs + concentration of 5% or 10%, while a higher concentration of GA + can deliver a better crystallinity for the perovskite films with Cs + & GA + . It is noted that the low-dimensional GA-related phases are not detected in the film with Cs + & GA + due to a relatively lower concentration of GA + in the film (<10%), [13,37] while the film formed from the PbI 2 and pure GAI (100%) will lead to the formation of GAPbI 3 and GA 2 PbI 4 , [45] as shown in Figure S18 in the Supporting Information. Figure 5c shows the absorption spectra of different perovskite films, and the film with Cs + & GA + exhibits a relatively smaller optical bandgap calculated from Tauc plots.…”

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confidence: 99%

Precise Control of Perovskite Crystallization Kinetics via Sequential A‐Site Doping

et al. 2020

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film deposition process to achieve desired morphology and microstructure. [2-6] Most of the high-efficiency PSCs were produced by either one-step or two-step fabrication methods. The very first MAPbI 3-based PSC was fabricated via a one-step spincoating process developed by Kojima et al. in 2009. [7] However, the one-step fabricated perovskite film typically exhibited a dendritic morphology with poor coverage. To address the morphology issue, a two-step spin-coating process was developed by Xiao et al. [8] and Im et al. [9] in 2014, which consisted of sequential depositions of an inorganic PbI 2 layer and an organic salt MAI. This two-step method gave rise to compact and pinhole-free MAPbI 3 perovskite films, significantly increasing the efficiency of MA-based PSCs to ≈17%. [9] In 2015, the record PCE received another boost through the development of a simpler antisolvent-assisted one-step method, which could form a very uniform perovskite thin film by promoting the crystallization process. [4,10] Meanwhile, MA cations were replaced by CH(NH 2) 2 + (FA) cations to improve the light Two-step-fabricated FAPbI 3-based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI 3-based perovskite film with sequential A-site doping of Cs + and GA + is revealed by in situ X-ray scattering and first-principles calculations. Incorporating Cs + in the first step induces an alternative pathway from δ-CsPbI 3 to perovskite α-phase, which is energetically more favorable than the conventional pathways from PbI 2. However, pinholes are formed due to the nonuniform nucleation with sparse δ-CsPbI 3 crystals. Fortunately, incorporating GA + in the second step can not only promote the phase transition from δ-CsPbI 3 to the perovskite α-phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two-step process over the one-step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.

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Enhanced Incorporation of Guanidinium in Formamidinium‐Based Perovskites for Efficient and Stable Photovoltaics: The Role of Cs and Br

Cited by 47 publications

References 33 publications

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs_{(1 − x)}Rb_xPbI₂Br Inorganic Perovskite Solar Cells

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs_{(1 − x)}Rb_xPbI₂Br Inorganic Perovskite Solar Cells

Stabilizing Perovskite Light‐Emitting Diodes by Incorporation of Binary Alkali Cations

Precise Control of Perovskite Crystallization Kinetics via Sequential A‐Site Doping

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Enhanced Incorporation of Guanidinium in Formamidinium‐Based Perovskites for Efficient and Stable Photovoltaics: The Role of Cs and Br

Cited by 47 publications

References 33 publications

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs(1 − x)RbxPbI2Br Inorganic Perovskite Solar Cells

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs(1 − x)RbxPbI2Br Inorganic Perovskite Solar Cells

Stabilizing Perovskite Light‐Emitting Diodes by Incorporation of Binary Alkali Cations

Precise Control of Perovskite Crystallization Kinetics via Sequential A‐Site Doping

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Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs_{(1 − x)}Rb_xPbI₂Br Inorganic Perovskite Solar Cells

Guanidinium Passivation for Air‐Stable Rubidium‐Incorporated Cs_{(1 − x)}Rb_xPbI₂Br Inorganic Perovskite Solar Cells