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Liquid-State Dithiocarbonate-Based Polymeric Additives with Monodispersity Rendering Perovskite Solar Cells with Exceptionally High Certified Photocurrent and Fill Factor
No full textDithiocarbonate-based non-hygroscopic polymers with a glass transition temperature (T-g) and polydispersity index (PDI) of approximate to 4 degrees C and 1, respectively, are synthesized through living cationic ring-opening polymerization. These liquid-state polymers are characterized by monodispersity based on the low T-g and PDI, rendering remarkable miscibility with the perovskite precursors without aggregation. Accordingly, these polymers are added to perovskite solar cells (PSCs) to enhance their power conversion efficiency (PCE). The PCE of reference PSCs increases from 19.70% to 23.52% after direct addition of the synthesized polymer. This efficiency improvement is attributed to the considerable increases in short-circuit current density (J(SC)) and fill factor (FF), resulting from the augmented size and defect passivation of perovskite crystals induced by added polymers. In fact, the PCE and J(SC) of the devices measured in the laboratory and the certification center are the highest among the reported polymer-added PSCs, thanks to the great miscibility of the new polymers leading to the large amount addition which enables more thorough passivation among the grain boundaries. The improvement in open-circuit voltage falls short as compared to that in J(SC) and FF, ascribed to the relatively moderate interaction strength between perovskite materials and dithiocarbonate groups
Calculation of exciton couplings based on density functional tight-binding coupled to state-interaction state-averaged ensemble-referenced Kohn-Sham approach
No full textWe introduce the combination of the density functional tight binding (DFTB) approach, including onsite correction (OC) and long-range corrected (LC) functional and the state-interaction state-averaged spin-restricted ensemble-referenced Kohn-Sham (SI-SA-REKS or SSR) method with extended active space involving four electrons and four orbitals [LC-OC-DFTB/SSR(4,4)], to investigate exciton couplings in multichromophoric systems, such as organic crystals and molecular aggregates. We employ the LC-OC-DFTB/SSR(4,4) method to calculate the excitonic coupling in anthracene and tetracene. As a result, the LC-OC-DFTB/SSR(4,4) method provides a reliable description of the locally excited (LE) state in a single chromophore and the excitonic couplings between chromophores with reasonable accuracy compared to the experiment and the conventional SSR(4,4) method. In addition, the thermal fluctuation of excitonic couplings from dynamic nuclear motion in an anthracene crystal with LC-OC-DFTB/SSR(4,4) shows a similar fluctuation of excitonic coupling and spectral density with those of first-principle calculations. We conclude that LC-OC-DFTB/SSR(4,4) is capable of providing reasonable features related to LE states, such as Frenkel exciton with efficient computational cost
Relationship of aerosol optical properties and particle types from SPARTAN and AERONET data in South Korea
No full textSPARTAN (Surface Particulate Matter Network) is a network of Particulate Matter (PM) samplers that analyze aerosol samples for PM mass concentration and chemical composition. Two aerosol samplers were installed at two sites in Korea: Yonsei University at Seoul and UNIST (Ulsan Institute of Science and Technology) at Ulsan. These SPARTAN filter samplers and additional nephelometers provide the PM2.5 mass concentration and reconstructed chemical speciation data (May, 2019~ Nov, 2021). In most SPARTAN PM2.5 cases, both sites showed time series patterns similar to data from the Korean regional observation network (Airkorea). In the case of high-loading fine dust, the daily value was relatively well matched with Airkorea data. The co-location of these SPARTAN samplers with AERONET (Aerosol Robotic Network) sun photometer presents the possibility of analyzing aerosol optical depth, aerosol surface mass concentration, and aerosol speciation data together. If the fraction of a particular component is high, the optical properties may vary. When the mass concentration of sulfate was relatively high, AERONET data displayed a large distribution of non-absorbing small particles. Similar to the previous analysis, we also show a detailed analysis of the relationship between other chemical components and optical properties
Benzo[1,2-b:4,5-b' ]Difuran-Based Polymer for Organic Solar Cells with 17.5% Efficiency via Halogenation-Mediated Aggregation Control
No full textThe realization of high-efficiency organic solar cells (OSCs) from renewable sources will bring a real green energy technology. Benzo[1,2-b:4,5-b ' ]difuran (BDF) is such a building block for photovoltaic polymers as it can be built from furfural, which is available from trees and vegetables. However, the device performance of BDF-based polymers is limited by aggregation properties and unfavorable active layer morphology. Herein, two new BDF-based wide bandgap-conjugated polymers, PFCT-2F and PFCT-2Cl, are developed by copolymerizing the fluorinated or chlorinated BDF units with the 3-cyanothiophene unit for use as electron donors in OSCs. Benefitting from the more rotatable nature of the side-chain thiophene rings on the BDF unit, PFCT-2Cl exhibits more adjustable aggregation, higher pi-pi stacking ordering, and appropriate miscibility with the electron acceptor. As a result, a high power conversion efficiency (PCE) of 17.2% is offered by PFCT-2Cl, which is nearly two times higher than that of PFCT-2F (8.9%). A more remarkable PCE up to 17.5% is further achieved by PFCT-2Cl in a ternary OSC, which is the new efficiency record for BDF-based polymers. This success proves the critical role of aggregation control in BDF-based polymers and the bright future for constructing high-performance OSCs from bio-renewable sources
Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks
No full textBecause of their designability and unprecedented synergistic effects, core-shell metal -organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral-and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single -crystalline core-shell synthesis with different kinds of MOFs
