Benzylamine is introduced as a surface passivation molecule that improves the moisture‐resistance of the perovskites while simultaneously enhancing their electronic properties. Solar cells based on ...benzylamine‐modified formamidinium lead iodide perovskite films exhibit a champion efficiency of 19.2% and an open‐circuit voltage of 1.12 V. The modified FAPbI3 films exhibit no degradation after >2800 h air exposure.
Methyl-ammonium lead iodide perovskite (CH
NH
PbI
) has drawn great attention due to its excellent photovoltaic properties. Because of its loosely compacted structure, the structural, electronic and ...optical properties of CH
NH
PbI
are sensitive to external modulations. Strain effects on CH
NH
PbI
are fully investigated by the first principles calculations. The results indicate that the inorganic framework deforms under compression or stretch and the embedded organic CH
NH
+ molecules rotate correspondingly. A band gap oscillation and a new structural phase in response to the external strain were observed for the first time. These phenomena are explained with the nonlinear structural deformation and phase transition under the external strains. The semi-quantitative relationship between the band gap variation and geometry change under the external strain is obtained. We found that the shift of valence band maximum under the external strain is mostly determined by the most stretched or compressed Pb-I bond of CH
NH
PbI
, and the shift of the conduction band minimum under the external strain is likely to be determined by the largest Pb-I-Pb bond angle in the system. These results are important for understanding of strain effects on semiconductors and guiding the experiments to improve the performance of the perovskite solar cells.
Charge carrier recombination plays a vital role in the CH3NH3PbI3 perovskite solar cell. By investigating a possible synergy between ion migration and charge carrier recombination, we demonstrate ...that the nonradiative recombination accelerates by an order of magnitude during iodide migration. The migration induces lattice distortion that brings electrons and holes close to each other and increases their electrostatic interactions. The wave function localization in the same spatial region, and the enhanced lattice and iodide movements increase the nonadiabatic coupling. At the same time, quantum coherence lasts longer, because electron and hole energy levels become correlated. All these factors greatly increase the recombination rate. Moreover, the energy level of the iodide vacancy created during the migration moves from inside the conduction band in the equilibrated structure into the band gap, acting as a typical efficient nonradiative charge recombination center. Our work shows that the different dynamic processes are strongly correlated in halide perovskites and demonstrates that defects, considered to be benign, can become very detrimental under non-equilibrium conditions. The reported results strongly suggest that ion migration should be avoided in halide perovskites, both for its own reasons, such as the large current–voltage hysteresis, and because it greatly accelerates charge carrier losses.
The use of electrode additives such as binder and conductive additive (CA) in addition to high pore volume for electrolytes, results in reduced volumetric energy densities of all battery electrodes. ...In this work, it is proposed to use poly(furfuryl alcohol) (PFA) conductive resin as a trifunctional electrode additive to replace polyvinylidene fluoride (PVDF) and CA while simultaneously enabling low porosity electrode function. The resultant PFA binder has a long‐range ordered structure of conjugated diene, which allow electronic conductivity that leads to a CA‐free electrode fabrication process. The oxygen heteroatoms in the PFA structure reduce the diffusion barriers of lithium ions, lowers the amount of required electrolyte/pore volume and thus, increasing electrode density. Serving as a trifunctional electrode additive, a high electrode density of 2.65 g cm−3 of the LiFePO4 (LFP) electrode and therefore the highest volumetric energy density of 1551 Wh L−1 so far. The LFP electrode using PFA binder can achieve a capacity retention of ≈80% and Coulombic efficiency of over 99.9% after cycling for 500 times. The proposed in situ polymerization strategy could revolutionize the electrode process, with the advantages of being simple, environmentally friendly, and easily scalable to industrial applications.
In situ polymerization of simple, low‐cost, and sustainable furfuryl alcohol is integrated into binder design for lithium ion battery electrodes, enabling a high electrode density of 2.65 g cm−3 for the LiFePO4 electrode and therefore the highest volumetric energy density of 1551 Wh L−1.
Conductive confinement of sulfur and polysulfides via carbonaceous blocking layers can simultaneously address the issues of low conductivity, volume expansion of sulfur during the charge/discharge ...process and the polysulfide shuttling effect in lithium-sulfur (Li-S) batteries. Herein, a conductive and porous nitrogen and phosphorus dual doped graphene (p-NP-G) blocking layer is prepared via a thermal annealing and subsequent hydrothermal reaction route. The doping levels of N and P in p-NP-G as measured by X-ray photoelectron spectroscopy are ca. 4.38% and ca. 1.93%, respectively. The dual doped blocking layer exhibits higher conductivity than N or P single doped blocking layers. More importantly, density functional theory (DFT) calculations demonstrate that P atoms and -P-O groups in the p-NP-G layer offer stronger adsorption of polysulfides than the N species. The electrochemical evaluation results illustrate that the p-NP-G blocking layer can deliver superior initial capacity (1158.3 mA h g super(-1) at a current density of 1C), excellent rate capability (633.7 mA h g super(-1) at 2C), and satisfactory cycling stability (ca. 0.09% capacity decay per cycle), which are better than those of the N or P single doped graphene. This work suggests that this synergetic combination of conductive and adsorptive confinement strategies induced by the multi-heteroatom doping scheme is a promising approach for developing high performance Li-S batteries.
On account of the scarcity of molecules with a satisfactory second near-infrared (NIR-II) response, the design of high-performance organic NIR photothermal materials has been limited. Herein, we ...investigate a cocrystal incorporating tetrathiafulvalene (TTF) and tetrachloroperylene dianhydride (TCPDA) components. A stable radical was generated through charge transfer from TTF to TCPDA, which exhibits strong and wide-ranging NIR-II absorption. The metal-free TTF-TCPDA cocrystal in this research shows high photothermal conversion capability under 1064 nm laser irradiation and clear photothermal imaging. The remarkable conversion ability-which is a result of twisted components in the cocrystal-has been demonstrated by analyses of single crystal X-ray diffraction, photoluminescence and femtosecond transient absorption spectroscopy as well as theoretical calculations. We have discovered that space charge separation and the ordered lattice in the TTF-TCPDA cocrystal suppress the radiative decay, while simultaneously strong intermolecular charge transfer enhances the non-radiative decay. The twisted TCPDA component induces rapid charge recombination, while the distorted configuration in TTF-TCPDA favors an internal non-radiative pathway. This research has provided a comprehensive understanding of the photothermal conversion mechanism and opened a new way for the design of advanced organic NIR-II photothermal materials.
we incorporated redox-active tetrathiafulvalene (TTF) and tetrachloroperylene dianhydride (TCPDA) into a cocrystal and its effective NIR-II photothermal which results from the twisted conformation was characterized and analysed.
Photogenerated radicals are an indispensable member of the state‐of‐the‐art photochromic material family, as they can effectively modulate the photoluminescence and photothermal conversion ...performance of radical‐induced photochromic complexes. Herein, two novel radical‐induced photochromic metal–organic frameworks (MOFs), Ag(TEPE)(AC) ⋅ 7/4H2O ⋅ 5/4EtOH (1) and Ag(TEPE)(NC) ⋅ 3H2O ⋅ EtOH (2), are reported. Distinctly different topological networks can be obtained by judiciously introducing alternative π‐conjugated anionic guests, including a new topological structure (named as sfm) first reported in this work, describing as 4,4,4,4‐c net. EPR data and UV–Vis spectra prove the radical‐induced photochromic mechanism. Dynamic photochromism exhibits tunability in a wide CIE color space, with a linear segment from yellow to red for 1, while a curved coordinate line for 2, resulting in colorful emission from blue to orange. Moreover, photogenerated TEPE* radicals effectively activate the near‐infrared (NIR) photothermal conversion effect of MOFs. Under 1 W cm−2 808 nm laser irradiation, the surface temperatures of photoproducts 1* and 2* can reach ~160 °C and ~120 °C, respectively, with competitive NIR photothermal conversion efficiencies η=51.8 % (1*) and 36.2 % (2*). This work develops a feasible electrostatic compensation strategy to accurately introduce photoactive anionic guests into MOFs to construct multifunctional radical‐induced photothermal conversion materials with tunable photoluminescence behavior.
The photogenerated radicals in silver(I) metal–organic frameworks with alternative topology devote to achieving wide CIE color space tunability and the switching of admirable NIR photothermal conversion.
Ion migration, hole trapping, and electron–hole recombination are common processes in metal halide perovskites. We demonstrate using ab initio non-adiabatic molecular dynamics and time-domain density ...functional theory that they are intricately related and strongly influence each other. The hole injection accelerates ion migration by decreasing the diffusion barrier and shortening the migration length. The injected hole also promotes the nonradiative charge recombination by strengthening electron–phonon interactions in the low-frequency region and prolonging the quantum coherence time. The synergy stems from the soft perovskite lattice and response of the valence band maximum to the Pb–I lattice distortion induced by the hole. This work provides important insights into the influence of ion mobility and hole injection on the performance of perovskite solar cells and suggests that high concentration of holes should be avoided.
Using first-principles density functional calculations, we investigate the structure and properties of three different grain boundaries (GBs) in the solar absorber material CdTe. Among the low ∑ ...value symmetric tilt GBs ∑3 (111), ∑3 (112), and ∑5 (310), we confirm that the ∑3 (111) is the most stable one but is relatively benign for carrier transport as it does not introduce any new states into the gap. The ∑3 (112) and ∑5 (310) GBs, however, are detrimental due to gap states induced by Te–Te and Cd–Cd dangling bonds. We systematically investigate the segregation of O, Se, Cl, Na, and Cu to the GBs and associated electronic properties. Our results show that co-doping with Cl and Na is predicted to be a viable approach passivating all gap states induced by dangling bonds in CdTe.
•Metal oxides or hydroxides coating sulfur-based composite are successfully prepared.•Large-scale synthesis can be realized via the facile wet ball-milling strategy.•Density functional theory (DFT) ...calculation is applied to calculate adsorption energy.•ZnO exhibits a higher adsorption energy for Li2S8 than that Ni(OH)2.•ZnO@sulphur/carbon nanotubes composite show excellent cycle and discharge performance.
Zinc oxide wrapped sulphur/carbon nanotubes (ZnO@S/CNT) and nickel hydroxide wrapped sulphur/carbon nanotubes (Ni(OH)2@S/CNT) nanocomposites are prepared using a simple, low cost and scalable ball-milling method. As the cathodes in Li-S batteries, the as-prepared ZnO@S/CNT composite illustrates a superior high initial capacity of 1663mAhg−1at a charge/discharge rate of 160mAg−1, and maintains a reversible capacity at approximately 942mAhg−1 after 70 cycles. While for Ni(OH)2@S/CNT composites, its initial capacity is also as high as 1331mAhg−1, but a poorer cycling stability is presented. When the charge/discharge current is increased to 1600mAg−1, a high reversible capacity of 698mAhg−1 after 200 cycles still can be obtained for the ZnO@S/CNT composite, far better than that of Ni(OH)2@S/CNT composites. The better cycling performance and high discharge capacity can be attributed to the strong interactions between ZnO and Sx2− species, which is verified by the density functional theory (DFT) calculation result that the ZnO exhibits a higher adsorption energy for Li2S8 than the Ni(OH)2.
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