Rectifying behavior and photovoltage effect in La1.3Sr1.7Mn2O7/SrTiO3-Nb heterostructure

We propose a doping method by using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to fill the grain boundary interstices of the methylammonium lead iodide (CH3NH3PbI3) perovskite for the elimination of pinholes. A sandwiched PCBM layer is also used between the perovskite and TiO2 layers to improve the interfacial contact. By using these two methods, the fabricated perovskite solar cells show a low hysteresis effect and high current density, which result from the improved compactness at the grain boundaries of the perovskite surface and the interface between the TiO2/perovskite layers. The theoretical and experimental results indicate that PCBM can effectively suppress carrier recombination, regardless of the interfacial layer or dopant. We also found that the dark current reduced during the analysis of dark state current-voltage ( I- V) characteristics. The slopes of the I- V curves for the fluorine-doped tin oxide/PCBM-doped perovskite/Au device reduce monotonically with the increase in the PCBM concentration from 0.01 to 0.1 wt %, which suggest the decreasing defects in the perovskite layer. By tuning the PCBM doping and controlling the preparation process, we have successfully fabricated a planar TiO2/PCBM-based PCBM-doped perovskite photovoltaic device that reaches a high current density of 22.6 mA/cm2 and an outstanding photoelectric conversion efficiency up to 18.3%. The controllability of the PCBM doping concentration and interfacial preparation shed light on further optimization of the photoelectric conversion efficiency of perovskite solar cells.

The metal–oxygen covalency of manganese oxides is the main factor affecting the degradation efficiency of persistent organic pollutants in water.

We investigate the consequences of dimensional confinement on halide double perovskites by synthesizing two-dimensional analogues of the recently reported three-dimensional double perovskite Cs2AgBiBr6. The layered perovskites (BA)4AgBiBr8 (1) and (BA)2CsAgBiBr7 (2) (BA = CH3(CH2)3NH3+) feature metal-halide sheets of mono and bilayer thickness, respectively, where the ordered double-perovskite lattice is partitioned by organic cations. Electronic structure calculations indicate that the indirect bandgap of Cs2AgBiBr6 becomes direct when the infinitely thick inorganic lattice is reduced to monolayer thickness. Calculations on model systems allow us to separate the effects of dimensional reduction from those of the accompanying structural distortions in the inorganic sublattice. Detailed optical characterization shows that the photophysical properties of 1 and 2 are markedly different than those of their well-studied lead-halide analogs. Hybrid layered derivatives of double perovskites substantially expand on the substitutional flexibility of halide perovskites to encompass greater compositional and electronic diversity.

Bismuth‐based ferroelectric oxide films including BiFeO 3 , Bi 2 WO 6 and BiVO 4 with different band structure are prepared by pulsed laser deposition method and used as n‐type semiconductors in photovoltaic devices. The oxide films are combined with p‐type organic semiconductor poly(3‐hexylthiophene) to form bilayer heterojunctions and their photovoltaic effects are systematically studied. Compared with some other oxide semiconductors, such as ZnO or TiO 2 , the bismuth‐based oxides exhibit wider absorption spectra and can induce higher external quantum efficiency, open circuit voltage, and power conversion efficiency of the hybrid devices, indicating that bismuth‐based oxides are promising materials for photovoltaic devices.

Enhancing perovskite solar cells efficiency through cesium fluoride mediated surface lead iodide modulation

The search for nontoxic and stable alternatives to halide perovskites has driven significant research into lead-free double perovskite compositions. Among these, layered variants offer unique properties, but their synthesis often relies on solvent or heat-intensive methods. Herein, we demonstrate a scalable and solvent-free mechanochemical approach for the synthesis of ⟨111⟩-oriented layered double perovskites (LDPs). Three distinct solid solutions, Cs4Cu1-xMnxSb2Cl12, Cs4Cd1-xMnxSb2Cl12 and Cs4Cd1-xMnxBi2Cl12 (x = 0-1), were successfully obtained in batch sizes of up to 5.0 g. All compounds can be obtained in less than 30 min and retain their expected optical properties, highlighting mechanochemistry as a green and scalable route to lead-free layered perovskites.

Dion–Jacobson (DJ) double perovskites have emerged as environmentally friendly candidates for X‐ray detection, owing to their prominent optoelectronic performance and highlighted structural rigidity. Despite considerable efforts, the exploration of polar DJ‐type double perovskites for self‐powered X‐ray detection remains scarce. Herein, by introducing a diamine spacer to increase the structural rigidity, the study has successfully designed a new polar 2D DJ‐type double perovskite of (HIA)2AgBiBr8 (1, HIA = histamine), and centimeter‐size crystals are successfully obtained for effective X‐ray detection. Structurally, 1 features the quantum‐confined motif comprised of the directionally arranged inorganic perovskite sheets and alternating organic spacing cations, which endows a large mobility‐lifetime (µτ) product up to 1.23 × 10−3 cm2 V−1 on the par with typical X‐ray sensing candidates (MAPbI3 wafers, µτ = 2 × 10−3 cm2 V−1). This attribute gives rise to a high sensitivity of 118 µCGyair−1 cm−2 to X‐ray illumination. Moreover, based on its polar structure, bulk photovoltaic effect with the photovoltage of ≈0.45 V is obtained in 1, which affords the driving source toward the self‐powered X‐ray photodetection. This work highlights the potential of DJ‐type double perovskites in high‐energy ray detection and opens avenues for exploring new functionalities of DJ double perovskites as smart photoelectric candidates.

Layered halide perovskites and double perovskites optoelectronic properties have recently been the subject of intense research. Layered double perovskites represent the merging of both worlds, and as such, have the potential to further expand the already vast space of optoelectronic properties and applications of halide perovskites. Despite having more than 40 known members, to date, only the <111>-oriented layered double perovskites: Cs4Cd1–xMnxBi2Cl12, have shown efficient photoluminescence (PL). In this work, we replaced Bi with Sb to further investigate the electronic structure and PL properties of these materials, resulting in two new families of layered inorganic perovskites alloys with full solubility. The first family, Cs4Cd1–xMnSb2Cl12, exhibits a PL emission at 605 nm ascribed to Mn2+ centers in octahedral coordination, and a maximum photoluminescence quantum yield PLQY of 28.5%. The second family of alloys, also with full solubility, Cs4Cd0.8Mn0.2(Sb1–yBiy)2Cl12, contains a fixed amount of Mn2+ and Cd2+ cations but different concentrations of the trivalent metals. This variability allows the tuning of the PL emission from 603 nm to 614 nm. We show that the decreased efficiency of the Cs4Cd1–xMnxSb2Cl12family compared to Cs4Cd1–xMnxBi2Cl12, is mostly due to a decreased spin-orbit coupling in Sb and the subsequent increased electronic delocalization compared to the Bi alloys, reducing the energy transfer to Mn2+ centers. This work lays out a roadmap to understand and achieve high photoluminescence efficiencies in layered double perovskites.

We designed and synthesized two phosphonic acid carbazole derivatives (3-(3,6-bis ((9,9-dimethyl-9H-fluoren-2-yl) (4-methoxyphenyl) amino)-9H-carbazol-9-yl)propyl) phosphonic acid (LS-W) and (3-(3,6-bis((4’-methoxy [1,1’-biphenyl]-4-yl))(4-methoxyphenyl)amino)-9H-carbazol-9-yl) propyl) phosphonic acid (LS-BR). The carbazole unit is used as the core of the molecular structure, and the asymmetric diphenylamine is connected to form a D-π-D-type electron-donating skeleton. Finally, the phosphonic acid group is introduced to modify the skeleton. In this paper, the interaction between LS-W and LS-BR with undoped poly [bis (4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA) was studied by using a bilayer hole-transport layer (HTL) device structure. The electron-donating structure of carbazole-asymmetric diphenylamine extends the π-π conjugation unit of the molecule, improves the film-forming properties of the molecule, and can form a stable π-π stacking between the HTL and the perovskite layer, reducing the nonradiative recombination of the interface layer. The LS-BR has a deeper HOMO energy level, which is close to the HOMO energy level of PTAA and matches the valence band maximum (VBM) of perovskite. Theoretical calculations show that LS-BR has a uniform distribution of the electron cloud, and its higher dipole moment promotes intimate contact between the HTL and the ITO layer. The results of open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS) show that the introduction of a bilayer hole transport material (HTM) can effectively reduce the charge recombination of the interface layer and delay the aging of the device. Under simulated AM 1.5 G irradiation (100 mW cm–2), the photoelectric conversion efficiency (PCEs), short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) of the LS-BR/PTAA device were 20.86%, 23.61 mA cm–2, 1.087 V, and 81.22%, respectively, which were significantly improved compared with those of the pure PTAA device.

Switchable photovoltaic and enhanced photoelectricity in a single PbS@CH3NH3PbI3 hybrid composite micro/nanowire

Perovskite solar cells (PSCs) have been attracted much attention due to their high-energy conversion effi-ciency and low production cost. However, the issues of stability and toxicity are still remained. Our group focuses on the fundamental studies of PSCs devices, including development of a series of materials for compact layer, active layer, hole transfer layer, as well as back electrode of PSCs. In this lecture, we will introduce current progress of several types of Pb-free perovskites solar cells and remaining issues, as well as present the recent results of our group in development of Pb-free perovskites and application for solar cells. Several Pb-free perovskites have been designed and synthesized in our gourp. The electronic and optical properties of the lead-free halide double perovskites Cs2NaBX6 (B = Sb and Bi; X = Cl, Br and I) were investigated by first-principles calculation to ascertain the potential application of solar energy conversion. The designed double perovskites also were synthesized and carried out the characterization. Another work is preparation of composite active layer of bismuth triiodide (BiI3) and a layered perovskite (CH3NH3)3Bi2I9 (MBI) by a simple solution method. The nano/macrostructures of composite active layer were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). We found that the nanostructures and morphology of Pb-free perovskites affect significantly the performance of the solar cells fabricated.

This thesis contributes to the investigation of solid-state systems with a strong coupling between electrons and the surrounding atomic lattice (phonons). One focus point of the thesis is the material class of $Pr_{1-x}Ca_{x}MnO_3$ (PCMO), a strongly correlated perovskite manganese oxide, which shows a photovoltaic effect that is highly influenced by the electron-phonon interactions present in the material. We use a theoretical model including electron, phonon, and spin degrees of freedom in a combined quantum-mechanical/classical description to investigate ground-state ordered phases and the breakdown of long-range orbital order in low-doped PCMO with increasing temperature. Our results support new experimental evidence that the spontaneous orbital-order phase transition takes place at much lower temperatures than previously believed and correlates with the onset of the photovoltaic effect. In the second part of the thesis, we analyze in more detail the ability of quantum-classical methods to describe non-adiabatic electron-phonon dynamics, which is needed for an adequate description of excited charge carriers in polaronic materials, e.g., after a photoexcitation. We present a detailed benchmark study of two such methods, multitrajectory Ehrenfest (MTE) and fewest-switches surface hopping (FSSH), in a prototypical system with electron-phonon coupling: the Holstein model. We discuss the strengths and weaknesses of both methods, with a special focus on the importance of various initial states. In most studied cases, the FSSH method yields a better description of both the mobility/spreading of the excited charge carrier and the electron-nuclear energy transfer, making it a suitable method for further analysis of the PCMO photovoltaic effect in future studies.

Photoelectrochemical aptasensor for ultrasensitive detection of MUC1 based on titanium dioxide/polypyrrole/carboxy polyethylene glycol hybrid anti-fouling interface.

In order to study the photoelectric properties of the adsorption of different metal atoms on a two-dimensional (2D) perovskite surface, in this article, we built many models of Ag, Au, and Bi atoms adsorbed on 2D perovskite. We studied the rules influencing 2D perovskite adsorbing metal atoms with different n values (the n value is the number of inorganic layers of 2D perovskite; here n = 1, 2, and 3). Based on n = 2 2D perovskite, we successively used Ag, Au, and Bi metal atoms to adsorb on the 2D perovskite surface. Firstly, we calculated their adsorption energies. Based on the lowest energy principle, we found that Bi atom adsorption on the 2D perovskite surface gave the most stable structure among the three metal adsorptions because the energy of the Bi adsorption system was the smallest. Secondly, the electron transport process takes place from the s to the p orbital when Au and Ag atoms adsorb on the 2D perovskite surface, but in the Bi atom adsorption, the electron transport process takes place from the p to the p orbital, because the p–p orbital transport energy is lower than that of the s–p orbital. Therefore, Bi atom adsorption on the 2D perovskite surface can improve charge carrier transfer. Thirdly, we calculated the bond angles and bond energies of different metal adsorptions on 2D perovskite. Bi adsorption has greater interaction with the surface atoms of 2D perovskite than Ag or Au atom adsorption, which effectively enhances the surface polarization effects, and enhances the photoelectric properties of 2D perovskite. The light absorption spectrum further confirms that Bi atom adsorption has a greater impact on the 2D perovskite than the action of Ag or Au adsorption. Finally, in an experiment, we fabricated a 2D perovskite solar cell with an ITO/PEDOT:PSS/2D perovskite/PEI/Ag (Au, Bi) structure. The Bi electrode solar cell achieves the highest photoelectric conversion efficiency (PCE) of 15.16% among the three cells with forward scanning, which is consistent with the theoretical analysis. We believe that the adsorption of metals like Bi on a 2D perovskite surface as an electrode is conducive to improving the charge transport performance.

Pressure-induced emission (PIE) associated with self-trapping excitons (STEs) in low-dimensional halide perovskites has attracted great attention for better materials-by-design. Here, using 2D layered double perovskite (C6 H5 CH2 CH2 NH3 + )4 AgBiBr8 as a model system, we advance a fundamental physicochemical mechanism of the PIE from the perspective of carrier dynamics and excited-state behaviors of local lattice distortion. We observed a pressure-driven STE transformation from dark to bright states, corresponding a strong broadband Stokes-shifted emission. Further theoretical analysis demonstrated that the suppressed lattice distortion and enhanced electronic dimensionality in the excited-state play an important role in the formation of stabilized bright STEs, which could manipulate the self-trapping energy and lattice deformation energy to form an energy barrier between the potential energy curves of ground- and excited-state, and enhance the electron-hole orbital overlap, respectively.