Recently, two-dimensional (2D) layered organic-inorganic hybrid perovskites have attracted a huge amount of interest due to their unique layered structure, and potential optical properties. However, amongst researchers it has long been disputed as to whether it is suitable for use as a photovoltaic material or light-emitting device. Here, we present a detailed theoretical investigation to discuss the photovoltaic and optoelectronic properties of a novel synthetic 2D layered perovskite (PEA)2PbI4. Based on the calculated geometric and electronic structure, charge carrier mobilities of the 2D layered (PEA)2PbI4 are predicted theoretically. In addition, the linear dichroism and exciton binding energies are also calculated. We found that the carrier mobilities of the 2D layered (PEA)2PbI4 reach the same order of magnitude as those of the optoelectronic material MoS2, but smaller than those of the photovoltaic material MAPbI3 and Si crystal, whereas exciton binding energies (Eb) enlarge with the thinning layers, being obviously higher than MAPbI3 and Si crystal. Moreover, the system exhibits a strong linear dichroism, suggesting weak absorption along the c axis in the visible spectrum, which is detrimental to photovoltaics. Our work provides a theoretical basis to prove that ultrathin two-dimensional (2D) materials may be potential candidates for optoelectronic detection devices, rather than solar absorbers.

The sub-band gap absorption in the ferroelectric lead-free hybrid perovskite.

Ab initio simulations combined with the Berry phase method are employed to investigate ferroelectric polarization of tetragonal CsPbBr3 crystals by applying hydrostatic pressure varying from 0 to 19 GPa; we find that the object research belongs to the P4mm space group. The calculated results show that the materials undergo a paraelectric-ferroelectric phase transition when the pressure increases to a critical value 15 GPa. The polarization is strongly enhanced and attains a high value of about 23 μC cm-2, owing to the increase in the ionic and electric contributions to the polarization under compressive strain. We present a detailed theoretical investigation to analyze the origin of polarization. The ionic polarization is mainly ascribed to the central displacements of Pb2+ cations and Br- anions induced by a highly distorted octahedral PbBr6- framework. Electronic structure calculations suggest that asymmetric hopping p orbital electrons of Br(3) ions are responsible for the enhancement in electric polarization. These discoveries suggest that tetragonal CsPbBr3 has significant potential in future ferroelectric applications, and this can broaden the application field from optoelectronics to ferroelectrics.

Despite great efforts devoted to the unusual optoelectronic properties for the bulk inorganic halide perovskites, overcoming the surface effects and bringing about selective growth in the specified surface termination are still a challenge. In this paper, we investigate the electronic structures, effective masses, carrier mobility, and optical properties of γ-CsSnI 3 with different terminations by employing density functional theory calculations. The calculated results show that the range of values of hole mobility is from 370.50 to 584.39 cm 2 /V s. Our results are close to the experimental data 400 cm 2 /V s. Moreover, we further predicted that the perfect CsI termination may exhibit better photovoltaic characteristics than the SnI 2 termination. On the basis of the stability of different surfaces and surface vacancies, an appropriate condition was obtained to suppress the I vacancies and promote the growth of perfect CsI-termination surface. This work also indicates that the electronic and optical properties of inorganic halide perovskites are tuned by selecting the proper surface, which is an important technique in the design of other optoelectronic devices.

Abstract. Atmospheric carbon monoxide (CO) concentrations have been decreasing since 2000 as observed by both satellite- and ground-based instruments, but global bottom-up emission inventories surprisingly estimate increasing anthropogenic CO emissions concurrently. In this study, we use a multi-species atmospheric Bayesian inversion approach to attribute satellite-observed atmospheric CO variations to its sources and sinks in order to achieve a full closure of the global CO budget during 2000–2017. Our observation constraints include satellite retrievals of the total column mole fraction of CO, formaldehyde (HCHO), and methane (CH4) that are all major components of the atmospheric CO cycle. Three inversions (i.e., 2000–2017, 2005–2017, and 2010–2017) are performed to use the observation data to the maximum extent possible as they become available and assess the consistency of inversion results to the assimilation of more trace gas species. We identify a declining trend in the global CO budget since 2000 (three inversions are broadly consistent during overlapping periods), driven by reduced anthropogenic emissions in the U.S. and Europe (both likely from the transport sector), and in China (likely from industry and residential sectors), as well as by reduced biomass burning emissions globally, especially in Equatorial Africa (associated with reduced burned areas). We show that the trends and drivers of the inversion-based CO budget are not affected by the inter-annual variation assumed for prior CO fluxes. All three inversions estimate that surface CO emissions contradict the global bottom-up inventories in the world's top two emitters for the sign of anthropogenic emission trends in China (e.g., here −0.8 ± 0.5 % yr−1 since 2000 while the prior gives 1.3 ± 0.4 % yr−1) and for the rate of anthropogenic emission increase in South Asia (e.g., here 1.0 ± 0.6 % yr−1 since 2000 smaller than 3.5 ± 0.4 % yr−1 in the prior inventory). The posterior model CO concentrations and trends agree well with independent ground-based observations and correct the prior model bias. The comparison of the three inversions with different observation constraints further suggests that the most complete constrained inversion that assimilates CO, HCHO, and CH4 has a good representation of the global CO budget, therefore matches best with independent observations, while the inversion only assimilating CO tends to underestimate both the decrease in anthropogenic CO emissions and the increase in the CO chemical production. The global CO budget data from all three inversions in this study can be accessed from https://doi.org/10.6084/m9.figshare.c.4454453.v1 (Zheng et al., 2019).

In recent years, two-dimensional (2D) organic–inorganic perovskites have been attracting considerable attention because of their unique performance and enhanced stability for photovoltaic solar cells or photoluminescent devices.

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The electronic properties of an MoS2 and graphene heterostructure are investigated by density functional calculations.