Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Olthof, Selina; Meerholz, Klaus

doi:10.1038/srep40267

Cited by 257 publications

(362 citation statements)

References 56 publications

(74 reference statements)

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“…[54] At this point it is worth summarizing the effects of the IL on the substrate and on the perovskite. [46,47,56] This is effectively what we see here in the WF shift of the perovskite, where as the WF of the substrate decreases, there is a corresponding decrease in the WF of the perovskite crystallized atop the substrate. This has previously been observed for various types of materials such as polymers, where the deposition of the polymer on a variety of different substrates causes a shift in the work func tion of the substrate.…”

Section: Resultssupporting

confidence: 62%

Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface

Noel

Habisreutinger

Wenger

et al. 2019

Advanced Energy Materials

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Halide perovskites are currently one of the most heavily researched emerging photovoltaic materials. Despite achieving remarkable power conversion efficiencies, perovskite solar cells have not yet achieved their full potential, with the interfaces between the perovskite and the charge‐selective layers being where most recombination losses occur. In this study, a fluorinated ionic liquid (IL) is employed to modify the perovskite/SnO2 interface. Using Kelvin probe and photoelectron spectroscopy measurements, it is shown that depositing the perovskite onto an IL‐treated substrate results in the crystallization of a perovskite film which has a more n‐type character, evidenced by a decrease of the work function and a shift of the Fermi level toward the conduction band. Photoluminescence spectroscopy and time‐resolved microwave conductivity are used to investigate the optoelectronic properties of the perovskite grown on neat and IL‐modified surfaces and it is found that the modified substrate yields a perovskite film which exhibits an order of magnitude lower trap density than the control. When incorporated into solar cells, this interface modification results in a reduction in the current–voltage hysteresis and an improvement in device performance, with the best performing devices achieving steady‐state PCEs exceeding 20%.

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Section: Resultssupporting

confidence: 62%

Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface

Noel

Habisreutinger

Wenger

et al. 2019

Advanced Energy Materials

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“…1b) than the diffusion in bulk MAPbI 3 crystal, possibly driven by the local electronic field in the vicinity of the interface. A previous photoemission study [27] reported that the stoichiometry of MAPbI 3 within a few nm of the interfaces can be affected by the substrates, and the interface can have a band bending as a result of the dipole formation, in contrast to the commonly assumed flat band condition. A comparative study on the device performance [4] also proposed the possibility of ionic accumulation at the interface causing a steep band bending at the interface and a flat band in the rest of perovskite in order to explain the insensitivity of V oc to the VBM of the HTMs.…”

mentioning

confidence: 97%

Direct Observation of Ultrafast Hole Injection from Lead Halide Perovskite by Differential Transient Transmission Spectroscopy

Ishioka

Barker

Yanagida

et al. 2017

J. Phys. Chem. Lett.

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Efficient charge separation at the interfaces between the perovskite and with the carrier transport layers is crucial for perovskite solar cells to achieve high power conversion efficiency. We systematically investigate the hole injection dynamics from MAPbI3 perovskite to three typical hole transport materials (HTMs) PEDOT:PSS, PTAA and NiOx by means of pump-probe transmission measurements. We photoexcite only near the MAPbI3/HTM interface or near the back surface, and measure the differential transient transmission between the two excitation configurations to extract the carrier dynamics directly related to the hole injection. The differential transmission signals directly monitor the hole injections to PTAA and PEDOT:PSS being complete within 1 and 2 ps, respectively, and that to NiOx exhibiting an additional slow process of 40 ps time scale. The obtained injection dynamics are discussed in comparison with the device performance of the solar cells containing the same MAPbI3/HTM interfaces.Lead halide perovskite photovoltatic cells have been developing rapidly in the past few years, with their power conversion efficiency (PCE) now exceeding 22% [1]. The perovskites are direct semiconductors, and their photovoltatics can in principle work as a model p-i-n diode [2]. The difficulty in the controlled impurity doping in the perovskites can be circumvented by sandwiching the perovskite film between thin layers of electron-and holetransporting materials (ETM and HTM) in the planar heterojunction structure [3]. These carrier transporting layers enable efficient and irreversible separation of the electrons and holes photoexcited in the perovskite, and thereby lead to the high PCE of the perovskite solar cells. Whereas various inorganic and organic materials have been explored as ETM and HTM based on their conduction band minimum (CBM) and valence band maximum (VBM) energies with respect to those of the perovskite, the actual device performance depends very weakly on the energy level offset [3,4] but can be significantly affected by other factors such as perovskite crystalline quality and interfacial defects [5,6].The charge separation dynamics can in principle be monitored directly by means of transient absorption (or transmission) measurements in the visible to teraherz ranges. The time scale of the charge injection from the perovskite to the HTM layer remain controversial despite the extensive previous studies [5][6][7][8][9][10][11][12][13][14], however. The time constant of the hole injection from CH3NH3PbI 3 (MAPbI 3 ) to spiro-OMeTAD in the previous reports, for example, scattered widely from <80 fs [7] to 0.7 ps [8,9] to 8 ps [10]. The hole injection to NiO x was reported to be complete on sub-picosecond time scale [11], whereas those * ishioka.kunie@nims.go.jp to poly(triarylamine) (PTAA), poly(3-hexylthiophee-2,5-diyl (P3HT), and poly [2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b'] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole) (PCPDTBT) were reported to occur on sub-nanosecond time scales [12]. The ...

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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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Substrate-dependent electronic structure and film formation of MAPbI3 perovskites

Cited by 257 publications

References 56 publications

Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface

Elucidating the Role of a Tetrafluoroborate‐Based Ionic Liquid at the n‐Type Oxide/Perovskite Interface

Direct Observation of Ultrafast Hole Injection from Lead Halide Perovskite by Differential Transient Transmission Spectroscopy

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

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