Formation and evolution of the unexpected PbI<sub>2</sub> phase at the interface during the growth of evaporated perovskite films

Xu, Haitao; Wu, Yuna; Cui, Jian; Ni, Chaowei; Xu, Fuzong; Jiang, Cai; Hong, Fung‐E; Fang, Zebo; Wang, Wenzhen; Zhu, Jingtao; Wang, Linjun; Xu, Run; Xu, Fei

doi:10.1039/c6cp02737g

Cited by 62 publications

(51 citation statements)

References 33 publications

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“…Here, the authors found the formation of a 0.5 nm thick PbI 2 interface layer that introduced a significant interface dipole and only a negligible band bending in the perovskite layer. In good agreement, Xu et al 34. found on various substrates an interface related PbI 2 signature using x-ray diffraction on MAPbI 3 deposited on top of indium tin oxide (ITO), PEDOT:PSS, Si, and glass.…”

supporting

confidence: 74%

Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Olthof

Meerholz

2017

Sci Rep

257

326

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We present investigations on the interface formation between the hybrid perovskite MAPbI3 and various substrates, covering a wide range of work functions. The perovskite films are incrementally evaporated in situ while the electronic structure is evaluated using photoelectron spectroscopy. Our results show that there is an induction period in the growth of the perovskite during which volatile compounds are formed, catalyzed by the substrate. The duration of the induction period depends strongly on the nature of the substrate material, and it can take up to 20–30 nm of formal precursor deposition before the surface is passivated and the perovskite film starts forming. The stoichiometry of the 2–3 nm thin passivation layer deviates from the expected perovskite stoichiometry, being rich in decomposition products of the organic cation. During the regular growth of the perovskite, our measurements show a deviation from the commonly assumed flat band condition, i.e., dipole formation and band bending dominate the interface. Overall, the nature of the substrate not only changes the energetic alignment of the perovskite, it can introduce gap states and influence the film formation and morphology. The possible impact on device performance is discussed.

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supporting

confidence: 74%

Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Olthof

Meerholz

2017

Sci Rep

257

326

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“…In particular, MAI seems to have a varying affinity to physisorb on certain substrates and might even decompose, which hinders the formation of the perovskite phase in the first few nanometers. [74,75] Nevertheless, this issue can be overcome by employing a fullerene intermediate layer, allowing the fabrication of perovskite solar cells with a high stabilized efficiency. [76] For more details on vapor-based techniques, we refer the reader to the recently published review by Ono et al [77] Another emerging research topic concerns lower-dimensional perovskites that form by substitution of the organic compound with bulkier molecules, generally employing longer alkylammonium chains.…”

Section: Alternatives To Solution-processed Thin Filmsmentioning

confidence: 99%

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Petrus

Schlipf

Cheng

et al. 2017

Advanced Energy Materials

317

201

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following statement: These materials can be processed from solution and yet exhibit optoelectronic materials properties described in classic solid-state physics textbooks. This unprecedented combination has led to photovoltaic devices that can be processed at room temperature and achieve performance levels similar to industry giant polycrystalline silicon, from a starting point of 3.8% in 2009. [1][2][3][4] The first light-emitting electrochemical cells [5] and diodes [6][7][8] have also been introduced recently, leading to tunable light emission spectra and internal quantum efficiencies exceeding 15%.The road towards these achievements has been marked by a constant improvement of perovskite deposition techniques fueled by our increasing understanding of the crystallization processes. The choice of deposition technique, either from solution or vapor, and the composition and order in which precursor species are applied has a great influence on the crystallization kinetics. Here, one can distinguish one-step methods where the perovskite is formed from a precursor mixture dissolved in a common solution, and two-step methods where the inorganic compound is deposited first and transformed to the perovskite phase later by addition of the organic constituents. [9][10][11] Furthermore, many parameters during processing can have an effect on the crystallization mechanism and consequently on film morphology, such as the choice of solvents, concentrations and processing additives that are often not incorporated into the final product. [11][12][13] We discuss this aspect in Section 2, where we focus our attention on the most commonly employed solution-based techniques. Additionally, as for any new technology trying to displace an incumbent technology, higher efficiencies, lower costs, reproducibility, stability, and sustainability are paramount. In particular, reproducibility has been a major challenge in perovskite solar cells from the beginning: small variations in morphology, like crystal size, film roughness, and pinholes can have detrimental effects on photovoltaic performance. [14] On the other hand, current-voltage measurements often showed a hysteresis that is rarely seen in other photovoltaic technologies. [15] These topics are highlighted in Sections 3 and 4. Finally, in Section 5 we discuss the framework for market introduction, such as cost reduction by choosing low-cost charge transport layers, or how the lifetime of perovskite absorbers can be extended by the choice of materials composition.Hybrid metal halide perovskites have become one of the hottest topics in optoelectronic materials research in recent years. Not only have they surpassed everyone's expectations and achieved similar performance as tried and true polycrystalline silicon photovoltaic devices, but they are also finding applications in a variety of different fields, including lighting. The main advantages of hybrid metal halide perovskites are simple processability, compatible with large-scale solution processing such as roll-to-roll printing, a...

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“…45,46 XPS analysis previously revealed that the total oxygen atomic concentration calculated from the integrated area under the core level O 1s increased for decreasing MAPbI 3 film thickness (Fig. 2a).…”

Section: -44mentioning

confidence: 99%

Understanding surface chemistry during MAPbI₃ spray deposition and its effect on photovoltaic performance

et al. 2017

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aIn recent years there has been significant research into organic-inorganic halide perovskites for photovoltaic applications and has resulted in power conversion efficiencies greater than 20%. A number of deposition techniques have been utilized to produce high quality perovskite films including thermal evaporation, single and two-step spin coating and vapor assisted processes. However, these laboratory based fabrication methods are not well matched with low costing, roll to roll processing that is associated with large scale manufacture. In this work we use a low costing and rapid spray coating technique to fabricate solution processed MAPbI 3 films with controlled film thickness achieved through modifying concentration/spray volume. Investigation into the chemical composition and film morphology showed differing surface chemistries for the different film thicknesses, altering the surface morphology from large micro grained structures to small distorted grain arrangements. We have then implemented spray deposited films into solar devices (ITO/TiO 2 /MAPbI 3 /Au) and have studied the current density-voltage (JV) characteristics including light soaking effects. Through optimizing the absorber thickness the short-circuit current density is increased from 4.9 mA cm À2 to 22.3 mA cm À2, increasing overall power conversion efficiency by a factor 45. Investigation into the performance of devices under continued illumination showed an inverse relationship existed between low efficiency (thick) MAPbI 3 films and high efficiency (thin) MAPbI 3 films, where the former displayed large increases in overall performance compared to the rapid degradation in the latter. We attribute device instabilities to the increase in defect density as a consequence of the spray-induced surface chemistry, leading to trap assisted recombination at the back electrode.

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Formation and evolution of the unexpected PbI₂ phase at the interface during the growth of evaporated perovskite films

Cited by 62 publications

References 33 publications

Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Understanding surface chemistry during MAPbI₃ spray deposition and its effect on photovoltaic performance

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Formation and evolution of the unexpected PbI2 phase at the interface during the growth of evaporated perovskite films

Cited by 62 publications

References 33 publications

Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Capturing the Sun: A Review of the Challenges and Perspectives of Perovskite Solar Cells

Understanding surface chemistry during MAPbI3 spray deposition and its effect on photovoltaic performance

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Product

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Formation and evolution of the unexpected PbI₂ phase at the interface during the growth of evaporated perovskite films

Understanding surface chemistry during MAPbI₃ spray deposition and its effect on photovoltaic performance