Charge Transfer at the PTCDA/Black Phosphorus Interface

The interfacial electronic structure at the organic–inorganic semiconductor interface plays an important role in determining the electrical and optical performance of organic-based devices. Here, we studied the molecular alignment and electronic structure of thermally deposited 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) molecules on cleaved black phosphorus using photoelectron spectroscopy. The work function of black phosphorus is substantially upped with an organic thin film, originating from the charge transfer from black phosphorus to PTCDA. According to our photoemission spectrum and theoretical simulation, we also define the interaction between PTCDA and black phosphorus as weak van de Waals physisorption, rather than bonding chemisorption. Furthermore, we show that PTCDA thin film can effectively isolate reactive oxygen species, thereby protecting BP surface oxidation and deterioration under ambient conditions. Our results suggest the possibility of manipulating interfacial electronic structures of black phosphorus interface by noncovalent with organic semiconductor, in particular for applications in high-performance organic–inorganic hybrid photovoltaic

Effects of Precursor Ratios and Annealing on Electronic Structure and Surface Composition of CH₃NH₃PbI₃ Perovskite Films

The electronic structure and surface composition of CH₃NH₃PbI₃ (MAPbI₃) films fabricated by one-step method with different precursor ratios of PbI₂ to CH₃NH₃I (PbI₂/MAI) have been investigated with ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It is found that the core levels of all components in the MAPbI₃ film shift toward lower binding energy with decreasing the precursor ratio of PbI₂/MAI, indicating that the electronic structures of the MAPbI₃ film can be adjusted by the precursor ratio of PbI₂/MAI. The elemental compositions of the MAPbI₃ film also depend on the precursor ratio and annealing process, and the compositions are strongly correlated to the electronic properties of the films. The electronic properties remain unchanged with an annealing at 110 °C. However, a core level shift of 0.5 eV toward higher binding energy is observed with an annealing at 150 °C, together with noticeable composition change from the XPS core level analysis. The distribution of all chemical components in the MAPbI₃ film is further investigated with angle-resolved XPS (AR-XPS). It is observed that annealing at 150 °C leads to relatively shallow distribution variations of I and Pb in the MAPbI₃ film, accompanied by infiltration of metallic Pb into the bulk

Interface Electronic Structure between Au and Black Phosphorus

The interface electronic structure between Au and black phosphorus has been investigated with ultraviolet and X-ray photoemission spectroscopy. We observed that Au clusters form at the initial Au deposition, and an interface dipole is observed at the interface between Au and BP. The outermost BP lattice is destroyed and unbonded P appears, which is due to the formation of metallic Au by the deposition of more than 8 Å Au. The unbonded P is surface segregated at 8–15 Å, and it is covered with further increasing of the Au thickness. These observations reveal the processes in the Au/BP interface and provide possible directions to fabricate high performance Au/BP-based device

From Water Oxidation to Reduction: Transformation from Ni_<i>x</i>Co_3–<i>x</i>O₄ Nanowires to NiCo/NiCoO_<i>x</i> Heterostructures

A homologous Ni–Co based nanowire catalyst pair, composed of Ni_<i>x</i>Co_3–<i>x</i>O₄ nanowires and NiCo/NiCoO_<i>x</i> nanohybrid, is developed for efficient overall water splitting. Ni_<i>x</i>Co_3–<i>x</i>O₄ nanowires are found as a highly active oxygen evolution reaction (OER) catalyst, and they are converted into a highly active hydrogen evolution reaction (HER) catalyst through hydrogenation treatment as NiCo/NiCoO_<i>x</i> heteronanostructures. An OER current density of 10 mA cm^–2 is obtained with the Ni_<i>x</i>Co_3–<i>x</i>O₄ nanowires under an overpotential of 337 mV in 1.0 M KOH, and an HER current density of 10 mA cm^–2 is obtained with the NiCo/NiCoO_<i>x</i> heteronanostructures at an overpotential of 155 mV. When integrated in an electrolyzer, these catalysts demonstrate a stable performance in water splitting

CuSbS₂ as a Promising Earth-Abundant Photovoltaic Absorber Material: A Combined Theoretical and Experimental Study

Recently, CuSbS₂ has been proposed as an alternative earth-abundant absorber material for thin film solar cells. However, no systematic study on the chemical, optical, and electrical properties of CuSbS₂ has been reported. Using density functional theory (DFT) calculations, we showed that CuSbS₂ has superior defect physics with extremely low concentration of recombination-center defects within the forbidden gap, espeically under the S rich condition. It has intrinsically p-type conductivity, which is determined by the dominant Cu vacancy (<i>V</i>_Cu) defects with the a shallow ionization level and the lowest formation energy. Using a hydrazine based solution process, phase-pure, highly crystalline CuSbS₂ film with large grain size was successfully obtained. Optical absorption investigation revealed that our CuSbS₂ has a direct band gap of 1.4 eV. Ultraviolet photoelectron spectroscopy (UPS) study showed that the conduction band and valence band are located at 3.85 eV and −5.25 eV relative to the vacuum level, respectively. As the calculations predicted, a p-type conductivity is observed in the Hall effect measurements with a hole concentration of ∼10¹⁸ cm^–3 and hole mobility of 49 cm²/(V s). Finally, we have built a prototype FTO/CuSbS₂/CdS/ZnO/ZnO:Al/Au solar cell and achieved 0.50% solar conversion efficiency. Our theoretical and experimental investigation confirmed that CuSbS₂ is indeed a very promising absorber material for solar cell application

Modification of Ultrathin NPB Interlayer on the Electronic Structures of the CH₃NH₃PbI₃/NPB/MoO₃ Interface

Modification of the ultrathin <i>N</i>,<i>N</i>′-Di­(1-naphthyl)-<i>N</i>,<i>N</i>′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) insertion layer on the electronic structures of the CH₃NH₃PbI₃ (MAPbI₃)/MoO₃ interfaces is investigated using ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It is found that when an ultrathin NPB insertion layer of 16 Å is inserted between MAPbI₃ and MoO₃, the chemical reaction between the latter two can be effectively suppressed, and a favorable energy-level alignment is achieved. The valence band maximum (VBM) or highest occupied molecular orbital (HOMO) at the MAPbI₃/NPB/MoO₃ interface facilitates the hole transportation from the MAPbI₃ layer through the NPB layer toward the NPB/MoO₃ interface. As a result, the holes can be efficiently extracted to the hole collection electrode due to the small energy offset between the conduction band minimum (CBM) of MoO₃ and the HOMO of NPB. Therefore, the modification by the ultrathin NPB interlayer on the electronic structures of the MAPbI₃/MoO₃ interface can greatly improve the hole extraction and thus enhance the power efficiency of the corresponding solar cells

Thermal Evaporation and Characterization of Sb₂Se₃ Thin Film for Substrate Sb₂Se₃/CdS Solar Cells

Sb₂Se₃ is a promising absorber material for photovoltaic cells because of its optimum band gap, strong optical absorption, simple phase and composition, and earth-abundant and nontoxic constituents. However, this material is rarely explored for photovoltaic application. Here we report Sb₂Se₃ solar cells fabricated from thermal evaporation. The rationale to choose thermal evaporation for Sb₂Se₃ film deposition was first discussed, followed by detailed characterization of Sb₂Se₃ film deposited onto FTO with different substrate temperatures. We then studied the optical absorption, photosensitivity, and band position of Sb₂Se₃ film, and finally a prototype photovoltaic device FTO/Sb₂Se₃/CdS/ZnO/ZnO:Al/Au was constructed, achieving an encouraging 2.1% solar conversion efficiency

Interfacial Electronic Structures of Photodetectors Based on C8BTBT/Perovskite

Comprehensive measurements of ultraviolet photoemission spectroscopy, X-ray photoemission spectroscopy, X-ray diffraction, and atomic force microscopy are adopted to investigate the corelevance of energy level alignment, molecular orientation, and film growth of Au/C8BTBT/perovskite interfaces. A small energy offset of valence band maximum of 0.06 eV between perovskite and C8BTBT makes hole transportation feasible. About 0.65 eV upward shift of energy levels is observed with the deposition of the Au film on C8BTBT, which enhances hole transportation to the Au electrode. The observations from the interface analysis are supported by a prototype photodetector of Au (80 nm)/C8BTBT (20 nm)/perovskite (100 nm) that exhibits excellent performances whose responsivity can reach up to 2.65 A W^–1, 4 times higher than the best CH₃NH₃PbI₃ photodetectors