Humidity-Induced Grain Boundaries in MAPbI<sub>3</sub> Perovskite Films

Li, Dan; Bretschneider, Simon A.; Bergmann, V.; Hermes, Ilka; Mars, Julian; Klasen, Alexander; Lu, Hao; Tremel, Wolfgang; Mezger, Markus; Butt, Hans‐Jürgen; Weber, Stefan A. L.; Berger, Rüdiger

doi:10.1021/acs.jpcc.6b00335

Cited by 108 publications

(117 citation statements)

References 41 publications

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“…[18][19][20] To date, most of the stability studies have been performed on perovskite films fabricated from stoichiometric precursor solutions (PbI2:MAI in 1:1 molar ratio) or with an excess of MAI. [17,[21][22][23] However, recently reported champion perovskite solar cells showing power conversion efficiencies (PCE) exceeding 20% contain a 5-10% molar excess of PbI2. [24][25][26][27][28] The remnant PbI2 excess within the final absorber layer is believed to improve perovskite crystallization and to reduce non-radiative recombination rates by passivation of crystal grain boundaries, which could explain the additional boost in PCE.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

et al. 2016

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We investigated the influence of moisture on CH3NH3PbI3 perovskite films and solar cells derived from non-stoichiometric precursor mixtures. We followed both the structural changes under controlled air humidity via in-situ X-ray diffraction, and the electronic behavior of devices prepared from these films. A small PbI2 excess in the films improved the stability of the perovskite compared to stoichiometric samples. We assign this to excess PbI2 layers at the perovskite grain boundaries or to the termination of the perovskite crystals with lead and iodine. In contrast, the MAI-excess films composed of smaller perovskite crystals showed increased electronic disorder and reduced device performance due to poor charge collection. Upon exposure to moisture followed by dehydration ("solvent annealing"), these films recrystallized to form larger, highly oriented crystals with fewer electronic defects and a remarkable improvement in photocurrent and photovoltaic efficiency.

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Section: Introductionmentioning

confidence: 99%

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

et al. 2016

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“…We find an increasing prevalence of small grains in deteriorated films that indicates grain fracturing. 37 Compared to the pristine film, the GBs become highly resistive and wider in the | S 11 | image, evidence of the accumulation of reduced-conductivity material and the apparent disappearance of local trap passivation. The S 11 image now also shows significant variations within individual grains with well-defined but small regions of reduced conductivity giving an overall granular appearance to the film.…”

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confidence: 99%

“…Under continued exposure and possibly further aided by light, the moisture is capable of penetrating into individual grains as well as GBs, leading to deterioration that ultimately leads to reduced PV performance. 25,37 …”

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Electronic and Morphological Inhomogeneities in Pristine and Deteriorated Perovskite Photovoltaic Films

et al. 2017

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We perform scanning microwave microscopy (SMM) to study the spatially varying electronic properties and related morphology of pristine and degraded methylammonium lead-halide (MAPI) perovskite films fabricated under different ambient humidity. We find that higher processing humidity leads to the emergence of increased conductivity at the grain boundaries but also correlates with the appearance of resistive grains that contain PbI2. Deteriorated films show larger and increasingly insulating grain boundaries as well as spatially localized regions of reduced conductivity within grains. These results suggest that while humidity during film fabrication primarily benefits device properties due to the passivation of traps at the grain boundaries and self-doping, it also results in the emergence of PbI2-containing grains. We further establish that MAPI film deterioration under ambient conditions proceeds via the spatially localized breakdown of film conductivity, both at grain boundaries and within grains, due to local variations in susceptibility to deterioration. These results confirm that PbI2 has both beneficial and adverse effects on device performance and provide new means for device optimization by revealing spatial variations in sample conductivity as well as morphological differences in resistance to sample deterioration.

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“…Despite its high performance, its practical use is limited by low thermal stability due to MA. 5,6 Many efforts have been made to improve the stability and lifetime by interfacial modification or compositional changes of the perovskite layer. 7,8 Formamidinium (FA)-based perovskite is used as an alternative to MAPbI 3 owing to the suitable band gap structure and thermal stability.…”

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Low-temperature and Ambient Air Processes of Amorphous SnO_x-based Mixed Halide Perovskite Planar Solar Cell

Pinpithak¹,

Chen²,

Kulkarni³

et al. 2017

Chem. Lett.

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Herein, we report an amorphous tin oxide (SnO x )-based planar solar cell using a mixed organic cation mixed halide perovskite ((FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 ) absorber prepared via low-temperature solution processes under the ambient air condition (relative humidity 40%). The device performance demonstrated power conversion efficiency (PCE) up to 16%. Additionally, the device with a SnO 2 compact layer (CL) also reveals superior lightharvesting properties under weak incident light in comparison with those of TiO 2 .Keywords: Perovskite solar cell | Tin oxide (SnO x ) | Mixed organic cation and halideHybrid organicinorganic halides perovskite compounds have attracted great attention of research communities due to their excellent optoelectronic properties backed by the microscale range of electronhole diffusion lengths, in addition to good lightharvesting ability. With its first trial reporting 3.8% of power conversion efficiency (PCE), the performance of perovskite solar cells has been rapidly evolved to PCE beyond 22% by improvement in the crystallization method.14 Methylammonium lead iodide (MAPbI 3 ) has been widely used as a perovskite absorber with band gap energy of 1.55 1.60 eV. Despite its high performance, its practical use is limited by low thermal stability due to MA. 5,6 Many efforts have been made to improve the stability and lifetime by interfacial modification or compositional changes of the perovskite layer. 7,8Formamidinium (FA)-based perovskite is used as an alternative to MAPbI 3 owing to the suitable band gap structure and thermal stability.9,10 Nevertheless, the inactive δ-phase (yellow phase) of FAPbI 3 usually appears at room temperature. To solve this, compositional engineering by doping a small amount of MA and/or Br ions in the optimal ratio can stabilize the active phase (α-phase) and improve the performance with PCE of over 17%. 11,12 With stabilized FA perovskite absorbers, it is also essential for future industrialization to establish a low-cost process for device manufacture. To minimize the production cost, low-temperature is an important prerequisite to realize the roll-to-roll printing process. In case of perovskite devices, electron transporting materials (ETLs) are required to meet this condition. Replacing metal oxide ETLs with low-temperature processed TiO 2 -graphene, 13 19 However, there are a few reports detailing the fabrication of tin oxide-based FA/MA perovskite via low-temperature solution processes exposed to ambient and humid atmosphere conditions. Schematic illustration of device fabrication is shown in Figure 1a, and the detail of procedures is provided in the Supporting Information (SI). Scanning electron microscope (SEM) images of the layered structures are given in Figures 1b 1d. A tin oxide thin layer was synthesized in situ on the surface of F-doped SnO 2 (FTO). Using SnCl 2 ¢2H 2 O as a source of precursor, 0.1 M of SnCl 2 solution in ethanol was spin-coated twice on Fdoped SnO 2 conductive glass. Pin hole-free and high transparency tin oxide thin film ...

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Humidity-Induced Grain Boundaries in MAPbI₃ Perovskite Films

Cited by 108 publications

References 41 publications

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

Electronic and Morphological Inhomogeneities in Pristine and Deteriorated Perovskite Photovoltaic Films

Low-temperature and Ambient Air Processes of Amorphous SnO_x-based Mixed Halide Perovskite Planar Solar Cell

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Humidity-Induced Grain Boundaries in MAPbI3 Perovskite Films

Cited by 108 publications

References 41 publications

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

The Influence of Water Vapor on the Stability and Processing of Hybrid Perovskite Solar Cells Made from Non‐Stoichiometric Precursor Mixtures

Electronic and Morphological Inhomogeneities in Pristine and Deteriorated Perovskite Photovoltaic Films

Low-temperature and Ambient Air Processes of Amorphous SnOx-based Mixed Halide Perovskite Planar Solar Cell

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Humidity-Induced Grain Boundaries in MAPbI₃ Perovskite Films

Low-temperature and Ambient Air Processes of Amorphous SnO_x-based Mixed Halide Perovskite Planar Solar Cell