Origin of High Electronic Quality in Structurally Disordered CH3NH3PbI3 and the Passivation Effect of Cl and O at Grain Boundaries

Yin, Wan‐Jian; Chen, Hangyan; Shi, Tingting; Wei, Su‐Huai; Yan, Yanfa

doi:10.1002/aelm.201500044

Cited by 195 publications

(206 citation statements)

References 57 publications

(74 reference statements)

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“…The lattice parameters a and c in tetragonal (space group I4/m) are changed, respectively, from 0.892 to 0.886 nm and from 1.261 to 1.251 nm. The apparent optical bandgap can vary by the Cl concentration in MAPbI 3 (Cl), Burstein-Moss effect (carrier concentration), quantum confinement effect, and/or grains and grain boundaries [9, 10, 26, 35–37]. The Burstein-Moss and quantum confinement effects are not pertinent to this system considering that the composition of perovskite was confirmed to be the same for all the cases, and the grain size was out of the regime where the quantum confinement effect works in [36, 37].…”

Section: Resultsmentioning

confidence: 99%

“…Generally, defects in grains or grain boundaries act as trap sites for the charge carriers and consequently decrease the charge collection efficiency [3–6]. Indeed, much effort aimed at the single-crystal perovskites caused successful results for the high photon-to-charge conversion efficiency [7–10]. Therefore, examining the strategies to control the crystallization for the defect reduction is necessary to achieve better-performing perovskite photovoltaics.…”

Section: Introductionmentioning

confidence: 99%

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Tailoring the Mesoscopic TiO2 Layer: Concomitant Parameters for Enabling High-Performance Perovskite Solar Cells

et al. 2017

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Architectural control over the mesoporous TiO2 film, a common electron-transport layer for organic-inorganic hybrid perovskite solar cells, is conducted by employing sub-micron sized polystyrene beads as sacrificial template. Such tailored TiO2 layer is shown to induce asymmetric enhancement of light absorption notably in the long-wavelength region with red-shifted absorption onset of perovskite, leading to ~20% increase of photocurrent and ~10% increase of power conversion efficiency. This enhancement is likely to be originated from the enlarged CH3NH3PbI3(Cl) grains residing in the sub-micron pores rather than from the effect of reduced perovskite-TiO2 interfacial area, which is supported from optical bandgap change, haze transmission of incident light, and one-diode model parameters correlated with the internal surface area of microporous TiO2 layers. With the templating strategy suggested, the necessity of proper hole-blocking method is discussed to prevent any direct contact of the large perovskite grains infiltrated into the intended pores of TiO2 scaffold, further mitigating the interfacial recombination and leading to ~20% improvement in power conversion efficiency compared with the control device using conventional solution-processed hole blocking TiO2. Thereby, the imperatives that originate from the structural engineering of the electron-transport layer are discussed to understand the governing elements for the improved device performance.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1809-7) contains supplementary material, which is available to authorized users.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tailoring the Mesoscopic TiO2 Layer: Concomitant Parameters for Enabling High-Performance Perovskite Solar Cells

et al. 2017

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“…of perovskite films prepared on spectrosil using the PbAc 2 and sol-eng methods and exposed to solar simulator illumination at various oxygen levels for 10 h. The pristine perovskite films prepared by both recipes exhibit a clear onset at 780 nm. [21,23,[50][51][52][53] By fitting the exponential increase in absorption at the band edge an Urbach energy (Eu) can be calculated, representing the degree of energetic disorder within the bulk of the film. At relatively low oxygen levels, the PbAc 2 absorption at 700 nm is reduced by less than 15%, while when the oxygen concentration is higher than 12%, the absorption starts to drop abruptly.…”

Section: Effect Of Degradation On the Optical Properties Of Perovskitmentioning

confidence: 99%

Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films

Sun

Faßl

Becker‐Koch

et al. 2017

Advanced Energy Materials

205

210

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photovoltaic technology, where lifetimes greater than 25 years are required. [2] Although the issue of device stability has attracted increased attention of the photovoltaic research community in the last two years, reports that systematically study the fundamental causes (e.g., heat, electrical stress, humidity, oxygen, (UV) light, chemical precursors, processing conditions, influence of film quality and morphology) and mechanisms limiting the material and device stability remain scarce. [2][3][4][5] While the degradation of methylammonium lead iodide (MAPbI 3 ) in humid air has been studied experimentally as well as theoretically and was long thought to be the main factor for material degradation in ambient environment, [6][7][8][9][10][11][12][13][14][15] studies exploring the influence of oxygen and light on the solar cell performance have only recently been reported. [16][17][18][19][20] It has been shown that photoexcited electrons in the perovskite layer can form superoxide (O 2 − ) via electron transfer to molecular oxygen, which through deprotonation of the methylammonium cation in turn results in irreversible material degradation. The severity of the degradation has been linked to the efficiency of electron extraction via the electron extracting layer (EEL): devices employing a compact-TiO 2 /mesoporous Al 2 O 3 or compact-TiO 2 as EELs degraded in dry air on a timescale of less than 1 h, while with the use of a mesoporous TiO 2 layer, an EEL which results in faster electron extraction, the lifetimes were significantly increased. However, in these reports only the degradation of complete photovoltaic device was reported, with limited information on the degradation of the perovskite active layer itself and the impact of its microstructure was not identified.In this work, we systematically study the degradation of MAPbI 3 films under precisely controlled exposure to various oxygen levels (0-20%) under simulated sunlight in order to shed light on the progression of perovskite degradation under these conditions. We investigate two types of perovskite layers that are formed using different fabrication methods. The two recipes allow us to include the effect of layer microstructure on the dynamics of oxygen-induced degradation. We characterize the electronic, optical, compositional, and structural properties of the degraded perovskite films and correlate these results This paper investigates the impact of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI 3 ) perovskite films upon exposure to light and oxygen. By comparing the oxygen induced degradation of perovskite films of different microstructure-fabricated using either a lead acetate trihydrate precursor or a solvent engineering technique-it is demonstrated that films with larger and more uniform grains and better electronic quality show a significantly reduced degradation compared to films with smaller, more irregular grains. The effect of degradation on the optical, compositional, and microstructural properties of the perovsk...

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“…Yin et al also suggested that chlorine and oxygen could spontaneously segregate into the grain boundaries and passivate those defect levels and deactivate the trap state. [53] Another way to minimize the negative impact of the grain boundaries was investigated by Son et al [54] They added excessive amounts of CH 3 NH 3 I to the precursor solution, and noted that at 6 mole-% excess, CH 3 NH 3 I layers formed at the perovskite grain boundaries, which helped suppress non-radiative recombination and formed highly conductive ionic pathways that improved electron and hole extraction at the grain. [54] Conductive AFM (c-AFM) was used to investigate the conductive properties at the grain boundaries through local current-voltage measurements, with Figure 4a,b showing a film without excess CH 3 NH 3 I and one with 6 mole-% excess, respectively.…”

Section: Grain Boundaries Passivation and Ion Migrationmentioning

confidence: 99%

Microstructural Characterisations of Perovskite Solar Cells – From Grains to Interfaces: Techniques, Features, and Challenges

Rothmann

Etheridge

et al. 2017

Advanced Energy Materials

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group of crystals that all share the same type of crystal structure based on CaTiO 3 , namely ABX 3 , with A cations, such as methylammonium (CH 3 NH 2 + ), formamidinium (CH(NH 2 ) 2 + ), and cesium (Cs + ); B cations such as tin (Sn 2+ ) and lead (Pb 2+ ); and halides, such as iodide (I − ), bromide (Br − ), and chloride (Cl − ), as the X anion. Since the first report of a solar cell using a hybrid organic-inorganic perovskite by Miyasaka et al. in 2009, the solar cells' efficiency has rapidly increased from 3.8% [2] to over 22.1% [3] certified for laboratoryscale devices. This rapid increase is due in part to intense efforts to develop novel device architectures that are energetically favorable for charge generation and extraction, coupled with basic studies detailing the intrinsic properties of the photoactive perovskite materials. [4] However, this record efficiency is still well below the theoretical limit of ≈31% for a singlejunction photovoltaic device. [5] Significant improvements in processing technologies are needed, which in turn require a detailed understanding of microstructures, interface structures, and overall architectures of the solar cell device."Microstructure", the fine structure of a material from the micrometer to the atomic scale, plays an important role in determining the performance of many types of solar cells in use and under development today. In single crystal photoactive materials like silicon, the intragrain defects, such as stacking faults and dislocations, attract significant research interest since these intragrain defects tend to be decorated by impurities, causing higher recombinative losses in these areas. [6] In polycrystalline materials, such as CdTe, grain boundaries have been found to be a limiting factor in solar cell performance due to an enhanced recombination at the grain boundaries. [7] Modification of the grain boundaries by chlorine can assist electron-hole pair separation and positively contribute to carrier collection efficiency. [7,8] Clearly, detailed knowledge of the microstructures in conventional solar cell materials has played a significant role in understanding and improving the underlying processes that govern overall solar cell performance. Further improvements in power conversion efficiency beyond the current record of 22.1%, as well as improved performance stability of perovskite solar cells, are therefore anticipated through in-depth characterization and understanding of their microstructures.Organic-inorganic hybrid perovskite solar cells form a new type of thin film photovoltaic technology, which has achieved extraordinary improvements in power conversion efficiency in a relatively short time. To further improve the efficiency and stability of the perovskite solar cells, it is critical to understand and control the microstructure of both the functional materials and their interfaces. Much effort has already been made to understand the microstructure of perovskite solar cells and its influence on their performance. This has proved particularly cha...

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Origin of High Electronic Quality in Structurally Disordered CH₃NH₃PbI₃ and the Passivation Effect of Cl and O at Grain Boundaries

Cited by 195 publications

References 57 publications

Tailoring the Mesoscopic TiO2 Layer: Concomitant Parameters for Enabling High-Performance Perovskite Solar Cells

Tailoring the Mesoscopic TiO2 Layer: Concomitant Parameters for Enabling High-Performance Perovskite Solar Cells

Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films

Microstructural Characterisations of Perovskite Solar Cells – From Grains to Interfaces: Techniques, Features, and Challenges

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