Cation Role in Structural and Electronic Properties of 3D Organic–Inorganic Halide Perovskites: A DFT Analysis

Solution-processed hybrid organolead trihalide (MAPbX 3 ) perovskite solar cells (PSCs) have now achieved 20.1% certified power conversion efficiencies (1), following a rapid surge of development since perovskite based devices were first reported in 2009 (2). A key to the success of PSCs is the long diffusion length of charge carriers in the absorber perovskite layer (3). This parameter is expected to depend strongly on film crystallinity and morphology. Thermally evaporated MAPbI 3 films fabricated using a Cl --based metal salt precursor were reported to exhibit carrier diffusion lengths three times those of the best solution-processed materials, yet no measurable Cl -was incorporated in the final films, hinting at amajor but unclear mechanism in the control of crystallinity and morphology (4, 5). These observations suggest that there may be room to improve upon already remarkable PSC efficiencies via the optimization of three key parameters: charge carrier lifetime, mobility, and diffusion length.The quest for further improvements in these three figures of merit motivated our exploration of experimental strategies for the synthesis of large single-crystal MAPbX 3 perovskites that would exhibit phase purity and macroscopic (millimeter) dimensions. Unfortunately, previously published methods failed to produce single crystals with macroscopic dimensions large enough to enable electrode deposition and practical characterization of electrical properties (6). Past efforts based on cooling-induced crystallizationwere hindered by (i) the limited extent to which solubility could be influenced by controlling temperature, (ii) the complications arising from temperature-dependent phase transitions inMAPbX3, and(iii) the impact of convective currents (arising from thermal gradients in the growth solution) that disturb the ordered growth of the crystals.We hypothesized that a strategy using antisolvent vapor-assisted crystallization (AVC), in which an appropriate antisolvent is slowly diffused into a solution containing the crystal precursors, could lead to the growth of sizableMAPbX3 crystals of high quality (with crack-free, smooth surfaces,well-shaped borders, and clear bulk transparency). Prior attempts to grow hybrid perovskite crystals with AVC have fallen short of these qualities-a fact we tentatively attributed to the use of alcohols as antisolvents (7). Alcohols act as good solvents for the organic salt MAX (8) due to solventsolute hydrogen bond interactions; as a result, they can solvate MA+ during the ionic assembly of the crystal, potentially disrupting long-range lattice order.We instead implemented AVC (Fig. 1A) using a solvent with high solubility and moderate coordination for MAX and PbX 2 [N,Ndimethylformamide (DMF) or g-butyrolactone (GBA)] and an antisolvent in which both perovskite precursors are completely insoluble [dichloromethane (DCM)]. We reasoned that DCM, unlike alcohols, is an extremely poor solvent for both MAX and PbX 2 and lacks the ability to form hydrogen bonds, thus minimizing asymmetric i...

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“…= ! = 6.02!Å, which is in a good agreement with previous results (40). The calculated bandgap with these cell parameter is !…”

Section: I-v Measurements (Sclc)supporting

confidence: 91%

Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals

Shi

Adinolfi

Comin

et al. 2015

Science

4,387

266

4,237

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“…The optimized structures were then used to calculate the electronic structures by the density functional theory and the non-equilibrium Green function formalism based code, Nanodcal. [15]). The K-points set was 20x20x20.…”

Section: Methodsmentioning

confidence: 99%

First-Principles Study on Electronic Structures of FAPbX3 (X = Cl, Br, I) Hybrid Perovskites

Pan¹,

Su²,

Hsu³

et al. 2016

JAN

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Abstract. Using first principles calculations, we investigate the geometric and electronic structures of organic-inorganic hybrid perovskite, FAPbX 3 (FA = CH(NH 2 ) 2 + ; X = Cl, Br, I). Since the organic molecule in the centre of the 3D hybrid perovskite is the key for its characteristics, here we compare FAPbX 3 with MAPbX 3 (MA = CH 3 NH 3 + ). The band gap of the former is smaller than the latter. Particularly, the calculated band gap of FAPbI 3 , 1.40 eV, is close to the experimental data, 1.41 eV. Furthermore, we analyze their orbitals, density of states and the spatial distribution of the charges, revealing that FAPbX 3 can produce and transfer more excitons than MAPbX 3 does.Keywords: Solar cell, formamidinium, methylammonium, geometric structure, band gap. IntroductionPerovskite solar cells (PSCs) have been the most promising devices towards the renewable energy generation recently, whose highest efficiency, 21.1%, was achieved in 2016 [1]. In addition to their efficient light absorption and high carrier mobility [2-4], they are semiconductors with adjustable band gaps, which have the benefits to absorb different wavelengths of light [5] and to fit into the solar devices well [6]. However, the performance of perovskite depends on its structural order which is temperaturedependent even in typical solar cell operating conditions. For example, methylammonium (MA, CH 3 NH 3 + ) lead iodide (PbI 3 ) undergoes a phase transition between tetragonal and cubic symmetry within 54 and 57 • C [7,8]. Increasing the temperature increases the kinetic energy of the organic molecule in the perovskite [9,10] and creates volatile molecular defects towards the structure degradation [11]. These factors affect the PSC durability. Improving the perovskite stability thus is the key issue for solar cells, and formamidinium (FA, CH(NH 2 ) 2 + ) cations were recently suggested, by plane-wave first-principles calculations, to replace MA inside the inorganic metrix [12,13], due to that the former can interact with the inorganic cage stronger than the latter does, to reduce the release of volatile species [13] or alter the covalent/ionic character of Pb-I bonds [12]. On the other hand, mixing FA with MA is experimentally shown to be a route to stabilize the perovskite [8,14] and improve the power conversion efficiency [14]. However, first-principles calculations with the linear combination of atomic orbital (LCAO) basis-set, which are economical and feasible for charge transport studies, on this issue are still limited to date. In this work, we investigate the geometric and electronic properties of organic-inorganic hybrid perovskite, FAPbX 3 (X = Cl, Br, I) from first principles. Particularly, their geometries, band structures, orbitals, density of states, and the charge densities are analysed, revealing the electronic and optical properties, as well as the stability, of such materials. In addition, we compare the band gap of FAPbI 3 with the measured data. Finally, we compare the electronic features of FAPbX 3 with MAPbX 3 . Comp...

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“…48,49 The lower conduction band of the perovskite is more dispersive than the upper valance band in p-s semiconductors. Due to strong s-p coupling around the maximum of valance band, the upper valance band of perovskite is dispersive.…”

mentioning

confidence: 99%

Mobile Charge-Induced Fluorescence Intermittency in Methylammonium Lead Bromide Perovskite

et al. 2015

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Organic-inorganic halide perovskite has emerged as a very promising material for solar cells due to its excellent photovoltaic enabling properties resulting in rapid increase in device efficiency over the last 3 years. Extensive knowledge and in-depth physical understanding in the excited state carrier dynamics are urgently required. Here we investigate the fluorescence intermittency (also known as blinking) in vapor-assisted fabricated CH3NH3PbBr3 perovskite. The evident fluorescence blinking is observed in a dense CH3NH3PbBr3 perovskite film that is composed of nanoparticles in close contact with each other. In the case of an isolated nanoparticle no fluorescence blinking is observed. The "ON" probability of fluorescence is dependent on the excitation intensity and exhibits a similar power rule to semiconductor quantum dots at higher excitation intensity. As the vapor-assisted fabricated CH3NH3PbBr3 perovskite film is a cluster of nanoparticles forming a dense film, it facilitates mobile charge migration between the nanoparticles and charge accumulation at the surface or at the boundary of the nanoparticles. This leads to enhanced Auger-like nonradiative recombination contributing to the fluorescence intermittency observed. This finding provides unique insight into the charge accumulation and migration and thus is of crucial importance for device design and improvement.

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Cation Role in Structural and Electronic Properties of 3D Organic–Inorganic Halide Perovskites: A DFT Analysis

Cited by 185 publications

References 41 publications

Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals

Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals

First-Principles Study on Electronic Structures of FAPbX3 (X = Cl, Br, I) Hybrid Perovskites

Mobile Charge-Induced Fluorescence Intermittency in Methylammonium Lead Bromide Perovskite

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