Crystallization Dynamics of Organolead Halide Perovskite by Real-Time X-ray Diffraction

ruthenium molecular dye, wide absorption range, direct and tunable bandgaps, superior charge carrier mobility, and long carrier diffusion length. [6,[43][44][45] Although it has been synthesized for over 100 years, Mitzi et al. were the first to investigate the electrical properties of tin-based perovskite in 1994, [46] which was later used in numerous devices, including field effect transistors (FETs) and LEDs. [47][48][49] The attention toward metal halide perovskites sparked yet again in 2009, [42] and they were later named one of the most promising emerging technologies in 2016. In brief, metal halide perovskites can be divided into two types based on their crystal structure motif: (i) 3D-structured perovskite (AMX 3 ) and (ii) 2D-structured perovskite (A 2 MX 4 ). The structure of the perovskite could either be 2D or 3D, while the dimensions of the perovskite probably belong to 0D-3D. The term "perovskite" implies to the general class of materials derived from an elemental composition of AMX 3 and demonstrates the crystal structure of perovskite crystal CaTiO 3 , where the divalent metal M resides at the body center and surrounded by six X-anions located at the face centers in an octahedral cluster. The MX 6 in the octahedral cluster may form an extended 3D structure by all-corner-connected type with A-cation sitting at the center. It could also form a 2D perovskite when the 3D perovskite network is cut into one-layer-thick slices along the 〈100〉 direction and separates them apart. In principle, 2D perovskite is the easiest to synthesize because of its natural layered structure, which is held together by weak van der Waals forces. Dou et al. reported the large-scale synthesis of the monolayer (C 4 H 9 NH 3 ) 2 -PbBr 4 by a chemical method. [50] Along the same lines, several groups have prepared and characterized nanomaterials composed of various forms of perovskites. [51][52][53] Also, our group has recently successfully prepared a low-dimensional mixed 2D/3D perovskite using the protonated salt of amino valeric acid iodide (AVAI) as an organic precursor mixed with PbI 2 , in which a yellowish film was containing needle-like crystallite formed. [54] In this topical review, we present the latest advances in the synthesis of low-dimensional perovskites and the growth mechanism to develop a strategy to achieve best performing devices. Later, we focus the instability and a cost-effective solution to circumvent this problem, which is vital for the eventual deployment of perovskite solar cells to consumers market. We present an analysis of the origins for instability in perovskite solar cells, and present a summary of the main achievements and possible future developments of these low-dimensional perovskite. [2,55] Perovskite solar cells have been heralded as one of the most promising emerging technologies in 2016 because of the very high power conversion efficiency of 22% and the low cost of generating electricity compared to even fossil fuels. These are formed with various dimensionalities and can be fully mani...

Section: Thermally Induced Chemical Decompositionmentioning

confidence: 99%

Low‐Dimensional Perovskites: From Synthesis to Stability in Perovskite Solar Cells

Yusoff

Nazeeruddin

2017

“…[37] This phenomenon was reported in several other publications dealing with different fabrication methods. [37,[56][57][58][59] In their study, Oesinghaus et al further suggested that the presence of Cl -promotes the dissolution of the PbI 2 layer, leading to more crystals oriented in (002) direction (cf. Figure 2f).…”

Section: Two-step (Sequential Deposition)mentioning

confidence: 98%

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

Petrus

Schlipf

Cheng

et al. 2017

312

201

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...

“…[45] The in-situ conversion mechanism can explain why MAPI crystals are frequently observed to be tilted by an angle χ = 55° when produced via 2-step deposition. [14,34,42,48,49] Thus, simply by tuning the porosity of the PbI 2 layer, e.g., by variation of the spin-coating temperature, it is possible to tune the crystal orientation of MAPI films (cf. Figure 3b-d).…”

Section: Research Newsmentioning

confidence: 99%

“…e,f) Reproduced with permission. [48] Copyright 2015, American Chemical Society. g) Exemplary 2D GIWAXS images where reflexes from individual grains were tracked during film annealing to monitor grain rotation.…”

Section: Research Newsmentioning

confidence: 99%

Structure of Organometal Halide Perovskite Films as Determined with Grazing‐Incidence X‐Ray Scattering Methods

Schlipf

Müller‐Buschbaum

2017

129

115

Grazing‐incidence X‐ray scattering (GIXS) methods have proven to be a valuable asset for investigating the morphology of thin films at different length scales. Consequently, GIXS has been applied to the fast‐progressing field of organometal halide perovskites. This exciting class of materials has propelled research in the areas of cheap and sustainable photovoltaics, light emitting devices, and optoelectronics in general. Especially, perovskite solar cells (PSC) have seen a remarkable rise in power conversion efficiencies, crossing the 20% mark after only five years of research. This research news outlines GIXS studies focusing on the most challenging research topics in the perovskite field today: Current–voltage hysteresis, device reproducibility, and long‐term stability of PSC are inherently linked to perovskite film morphology. On the other hand, film formation depends on the choice of precursors and processing parameters; understanding their interdependence opens possibilities to tailor film morphologies. Owing to their tunability and moisture resistance, 2D perovskites have recently attracted attention. Examples of GIXS studies with different measurement and data analysis techniques are presented, highlighting especially in‐situ investigations on the many kinetic processes involved. Thus, an overview on the toolbox of GIXS techniques is linked to the specific needs of research into organometal halide perovskite optoelectronics.