Organic-inorganic Hybrid CH3NH3PbI3 Research Articles

Temperature Sensitive and Reversible Halide Ion Exchange in Inorganic–Organic Hybrid CH3NH3PbI3−xBrx Mixed-Halide Perovskite

Ion exchange of organic-inorganic hybrid perovskite plays a significant role in controlling the performance of materials ant its devices. In this study, an interesting phenomenon was observed that the precipitate in suspension (CH3NH3PbI3−xBrx in γ-butyrolactone) brought out different colors at high and room temperature. The mechanism study appears that the phenomenon is controlled by temperature sensitive and reversible halide ion exchange in organic-inorganic hybrid CH3NH3PbI3−xBrx mixed-halide perovskite. The results of structure phase, element composition morphology and band gap illustrate that high temperature 55 °C is beneficial to the increasing of I content in MAPbI3−xBrx and room temperature or lower is advantageous to increasing of Br content in MAPbI3−xBrx. Compared with MAPbI0.76Br2.24 precipitate acquired at room temperature, MAPbI1.17Br1.83 precipitate got at high temperature illustrate wider lattice spacing, better crystallinity, better morphology and narrower band gap. The results and findings in this study will prompt the interest of readers or experts in the field of organic-inorganic hybrid perovskite materials and related optoelectronic applications.

Effect of additive polarity on the stability of organic-inorganic hybrid CH3NH3PbI3 perovskite thin film

Synthesis of organic-inorganic hybrid CH3NH3PbI3 perovskite thin film from Pb(NO3)2 precursor was carried out by using alcohol with various polarity (isopropanol, 1-butanol and 1-propanol) as the additive. Preparation of CH3NH3PbI3 perovskite thin film was conducted by firstly forming Pb(NO3)2 thin film as the film’s precursor using spin coating method at 2500 rpm for 30 s with DMSO as the main solvent and isopropanol, 1-butanol or 1-propanol as the solvent additives. Pb(NO3)2 thin film was immersed in methyl ammonium iodide solution for 30 min to produce CH3NH3PbI3 perovskite thin film. The effect of solvent additive polarity on the grain size of perovskite film was studied using electron microscope method. Stability of CH3NH3PbI3 perovskite thin film was studied by using XRD and SEM. The result showed that increasing polarity of the solvent additives resulted in decreasing on the crystallinity of Pb(NO3)2 thin film. Pb(NO3)2 thin film with low crystallinity yielded high purity of CH3NH3PbI3 perovskite thin film with grain size up to 2.45 μm and have good stability with 43.09% degradation percentage for 24 h.

Direct atomic scale characterization of the surface structure and planar defects in the organic-inorganic hybrid CH3NH3PbI3 by Cryo-TEM

Abstract The performance of halide perovskite solar cells is often dominated by structural defects. However, atomic scale characterization of the crystalline defects in organic–inorganic hybrid perovskites is hindered by the electron-beam sensitivity of the organic components in the structure. Here we reported the atomic scale characterization of CH3NH3PbI3 (MAPbI3) single crystal using the state-of-the-art cryo-transmission electron microscopy. We confirm that the MAPbI3 structure is intact during high resolution cryo-TEM analysis by probing the content of carbon, nitrogen from the [CH3NH3]+ component using electron energy loss spectroscopy. Atomic steps of {200}T surfaces were observed which shed light on the crystal growth details and low-energy surfaces. Surprisingly, high density of stacking faults are observed in the hybrid perovskite materials. We believe these fault structures serves the role of micro-interface between otherwise perfect lattices which facilitates charge separation and reduces the photon-generated carrier recombination within the crystal solids. First-principles calculations show that the presence of such stacking faults significantly changes the electronic structures of the materials, which may play a critical role in further optimizing the properties such as charge-carrier mobility, the carrier diffusion length and energy conversion efficiency of organic-inorganic hybrid perovskite-based energy harvesting devices.

Large and Dense Organic-Inorganic Hybrid Perovskite CH3NH3PbI3 Wafer Fabricated by One-Step Reactive Direct Wafer Production with High X-ray Sensitivity.

Lead halide perovskites with good optoelectronic properties and high attenuation of high-energy radiation are great candidates for X-ray radiation detectors. Large area, dense, and thick films or wafers are a prerequisite for these applications. In this paper, a one-step heat-assisted high-pressure press method is developed to directly prepare a large (the largest has a diameter of 80 mm) and thickness- and shape-controlled phase-pure organic-inorganic hybrid CH3NH3PbI3 wafer of densely packed large microcrystals from raw powder materials. Meanwhile, this method uses no solvent to achieve essentially 100% material utilization. The obtained wafers show good ambipolar carrier mobilities of ∼20 cm2 V-1 s-1 and a μτ product as high as 3.84 × 10-4 cm2 V-1. Under an X-ray source using an acceleration voltage of 40 kV, the perovskite wafer-based X-ray detector shows an X-ray sensitivity as large as 1.22 × 105 μC Gyair-1 cm-2 under a 10 V bias, the highest reported for any perovskite material. The method provides a convenient strategy for producing large perovskite wafers with good optoelectronic properties, which will facilitate the development of large perovskite devices.

Why cannot all divalent cations completely substitute the Pb cations of CH3NH3PbI3 perovskite?

Organic-inorganic hybrid CH3NH3PbI3 perovskite has a great potential for applications in low-cost photovoltaic devices. However, the doped and substitution of Pb sites in CH3NH3PbI3 has not been widely reported. In this article, a quantum mechanical model was applied to determine why all divalent cations cannot substitute the Pb cations of CH3NH3PbI3 perovskite. The evaluation was performed by comparison the model with experimental results. On this basis, we carefully examined 42 types of cations and identified only nine kinds of cations including Ca2+, Sr2+, Sc2+, Ti2+, V2+, Y2+, Zr2+, Nb2+ and Sn2+ for doped into Pb sites. In these cases, it is expected that the corresponding compound would be single phase. Finally, an analysis was performed based on first principle, and the results indicate that divalent cations substituting the Pb sites modify the band structure and influence the performance of perovskite-based photostatics.

First-principles study on CH3NH3PbI3 materials for perovskite solar cells

CH3NH3PbI3 system of organic-inorganic hybrid perovskite structure solar cells absorption material was established by using first-principle calculations based on density functional theory (DFT). Orthorhombic CH3NH3PbI3 system model is optimized by different functional theories of CASTEP in Materials Studio. It revealed that the results of WC/GGA calculation method are more close to the experimental value. Electron band structure, state density are calculated in the paper and the results indicated that top orbital of the valence band is mainly contributed by Pb atom and I atomic orbital. At the same time, the conduction band bottom is mainly contributed by the orbital contribution of Pb atoms and strong σ bond is formed between terminal iodine atom and Pb atomic orbital. Moreover, the contribution of organic element density of states near the Fermi surface is very weak and the band gap of organic-inorganic hybrid CH3NH3PbI3 materials is basically determined by inorganic elements.

Recent progress in Pb-free stable inorganic double halide perovskites

Although the power conversion efficiency (PCE) of CH3NH3PbI3-based solar cells has achieved 22.1%, which is comparable to commercialized thin-film CdTe and Cu(In,Ga)Se2 solar cells, the long-term stability is the main obstacle for the commercialization of perovskite solar cells. Recent efforts have been made to explore alternative inorganic perovskites, which were assumed to have better stability than organic-inorganic hybrid CH3NH3PbI3. In this short review, we will keep up with experiments and summarize recent progresses of inorganic double halide perovskite, in particular to Cs2AgBiBr6, Cs2AgInCl6, Cs2InBiBr6 and their family members. We will also share our opinions on the promise of such class of materials.

(Invited) Photophysics of Lead Halide Perovskite Solar Cells

Very recently, lead-halide perovskites have received much attention as a promising class of low-cost and high-performance photovoltaics materials since the first report of all-solid-state perovskite solar cells (SCs) in 2012 [1]. Organic-inorganic hybrid CH3NH3PbI3 is a model material of metal-halide perovskites, and its optical and electronic properties have been insensitively studied. It is known that perovskite CH3NH3PbI3 has excellent optoelectronic properties for SC applications: large optical absorption coefficients, extremely low densities of traps and defects, and long diffusion lengths of carriers. Because the energy conversion efficiencies of SCs depend on the luminescence quantum efficiency of the target semiconductor material [2,3], photoluminescence (PL) spectroscopy is one of the most powerful techniques for characterizing and developing new materials and structures for SC devices. By taking advantage of high-efficiency PL of lead-halide perovskites, we can directly monitor their carrier generation, recombination, and transport dynamics of SCs using time-resolved PL spectroscopy [4]. Here, we summarize the optical properties of solution-processed CH3NH3PbI3 and CH3NH3PbBr3thin films and single crystals and discuss the physical origin of high conversion efficiencies in perovskite SCs. Optical studies on high-quality thin films and single crystals are required for a deep understanding of the intrinsic optoelectronic properties of lead-halide perovskites. We studied photocarrier dynamics of high-quality CH3NH3PbI3 and CH3NH3PbBr3thin films and single crystals using one-photon excited PL (1PL) and two-photon excited PL (2PL) spectroscopy [5-7]. In thick single crystals, the photocarriers are generated at the near-surface region under one-photon excitation and in the interior region under two-photon excitation. The time-integrated 1PL peak energy is higher than the 2PL peak energy. The 1PL peak energy shifts to lower energy with delay time after laser excitation. The 1PL lifetime is shorter than the 2PL lifetime. These dynamical PL behaviors of thick single crystals are different from those of thin films. In thin films, the photocarriers are created homogeneously throughout the sample thickness under one- and two-photon excitation [8]. The spatial distribution of photocarriers determines the PL spectrum and dynamics: The PL dynamics of thick single crystals can be explained by fast carrier diffusion and photon recycling (photon emission and reabsorption) [5-7]. In SC device structures, the perovskite CH3NH3PbI3 layer is sandwiched between the mesoporous TiO2electron-transport layer and the spiro-OMeTAD hole-transport layer. Charge carrier dynamics in the perovskite solar cells were studied by means of PL and photocurrent (PC) imaging spectroscopy. Simultaneous PL and PC imaging measurements revealed a positive correlation between the PL intensity and PL lifetime, and a negative correlation between PL and PC intensities [8]. These correlations are a result of the competition between the escape of photocarriers from the perovskite layer and the recombination of photocarriers within the perovskite layer. Moreover, from the excitation-fluence dependence of the PL decay curves in thin films and SCs, we conclude that the carrier injection at the interface determines the device performance of perovskite SC [9,10]. Our systematic PL studies provide an essential information for developing high-performance devices based on metal-halide perovskites. Part of this work was supported by JST-CREST (Grant No. JPMJCR16N3). References M.M. Lee et al, Science 338, 643 (2012). O. D. Miller et al., IEEE J. Photovoltaics 2, 303 (2012). L. Zhu et al., Opt. Express 24, A740 (2016). Y. Kanemitsu, J. Mater. Chem. C 5, 3427 (2017). Y. Yamada et al., J. Am. Chem. Soc. 137, 10456 (2015). T. Yamada et al., Adv. Electron. Mater. 2, 1500290 (2016). T. Yamada et al., Phys. Rev. Applied. 7, 014001 (2017). Y. Yamada et al., J. Am. Chem. Soc. 136, 11610 (2014). D. Yamashita et al., J. Phys. Chem. Lett. 7, 3186 (2016). T. Handa et al., J. Phys. Chem. Lett. 8, 954 (2017). D. M. Tex et al., Phys. Rev. Applied 7, 014019 (2017).

Recent progress of organohalide perovskite solar cells

Since 2009, greater attention has been paid to organic-inorganic hybrid CH3NH3PbI3 solar cells because of their simple fabrication process and high power conversion efficiency. Organohalide perovskite solar cells now develop very fast and their photovoltaic performance has been gradually improved. However, because of a band-gap limitation, the sunlight absorption spectrum of CH3NH3PbI3 is not broad enough to produce enhanced photovoltaic properties. In addition, Pb, as an important element, is toxic in organohalide perovskite. Thus, it is significant and meaningful to fabricate narrow-gap, environmentally friendly organohalide perovskite solar cells with better chemical stability. In the present paper, we mainly reviewed the progress in the band-gap engineering of perovskite materials to identify elements to replace toxic Pb and improve the absorption efficiency of incident light and the photovoltaic performance of solar cells. The influences of organic and inorganic hole transporting materials on the power conversion efficiencies of devices were compared, followed by a discussion of the recent progress in hole-conductor-free solar cells. To date, the theoretical research on organohalide perovskites is neither fully comprehensive nor far-reaching. We then conducted a review of the progress of theoretical research on the atomic structure, band structure, and band gap of CH3NH3PbI3 and other analog perovskite materials. The advantages and disadvantages of popular theoretical methods and their issues, which would be helpful for developing computational work, are also discussed. Finally, we include a number of open questions relevant to this field and present some research topics for the future.