Kongchao Shen

On-surface manipulation of atom substitution between cobalt phthalocyanine and the Cu(111) substrate

On-surface fabrication of controllable nanostructures is an appealing topic in the field of molecular electronics. Herein, the adsorption of cobalt phthalocyanine (CoPc) on a Cu(111) surface is investigated utilizing a combination of photoelectron spectroscopy (PES) and density functional theory (DFT). Interestingly, the scenario of atom exchange is discovered at the interface at room temperature (RT), namely the substitution of the cobalt atom in CoPc by a surface Cu adatom. Moreover, thermal annealing enhances the substitution process considerably which is demonstrated to be complete at about 573 K. As revealed by DFT calculations, the driving force for the observed interface transmetalation is most probably provided by the initial strong molecular-substrate interaction between Co atoms and the Cu(111) surface, the external thermodynamic energy gained from thermal sublimation and thermal annealing, and the tendency to form Co–Cu alloy at the interface. While CoPc has been successfully utilized in electrocatalysts for fuel cell applications and CuPc is commonly used as a leading material in organic solar cells, this report of interface transmetalation from CoPc to CuPc in a solid state environment may offer an encouraging approach towards the artificial engineering of organometallic nanostructures and related properties for surface catalysts, molecular electronics and so on.

Graphene oxide as an additive to improve perovskite film crystallization and morphology for high-efficiency solar cells

The quality of a perovskite film has a great impact on its light absorption and carrier transport, which is vital to improve high-efficiency perovskite solar cells (PSCs). Herein, it is demonstrated that graphene oxide (GO) can be used as an effective additive in the precursor solution for the preparation of high-quality solution-processed CH3NH3PbI3 (MAIPbI3) films. It is evidenced by scanning electron microscopy that the size of the grains inside these films not only increases but also becomes more uniform after the introduction of an optimized amount of 1 vol% GO. Moreover, 1 vol% GO also enhances the crystallization of perovskite film with intact preferential out-of-plane orientation as proven by 2-dimensional grazing-incidence X-ray diffraction. As a consequence of the improved film quality, enhanced charge extraction efficiency and optical absorption are demonstrated by photoluminescence (PL) spectroscopy and UV-visible absorption spectroscopy, respectively. Using 1 vol% GO, the fabricated champion heterojunction PSC with a structure of ITO/SnO2/perovskite/spiro-OMeTAD/Au shows a significant power conversion efficiency increase to 17.59% with reduced hysteresis from 16.10% for the champion device based on pristine perovskite. The present study thus proposes a simple approach to make use of GO as an effective and cheap addictive for high-performance PSCs with large-scale production capability.

Performance Improvement of CH3NH3PbI3 Perovskite Solar Cell by CH3SH Doping

Organometal halide perovskites have recently emerged as an appealing candidate in photovoltaic devices due to their excellent properties. Therefore, intense efforts have been devoted to find the ideal organics for perovskite solar cells. In response, we investigate the doping effect of CH3SH organic on the structure and related performance of a CH3NH3PbI3 perovskite solar cell, via in situ synchrotron-based grazing incidence X-ray diffraction (GIXRD), together with scanning electron microscopy (SEM). In situ GIXRD investigations clearly illustrated the transformation and modification of the perovskite structure induced by the organic dopant, which subsequently led to the enhancement of the power conversion efficiency of fabricated solar cells. Notably, nanoporous morphology and nanocrystalline structures were discovered in the perovskite film by SEM; they were also confirmed by the increase in broadening peaks/features in the GIXRD measurements. Overall, our study may ultimately result in an attractive strategy for the fabrication of high performance perovskite solar cells.

Fabrication and Characterization of Organic–Inorganic Hybrid Perovskite Devices with External Doping

Owing to its excellent light harvesting, high-charge carrier mobility, and long electronand hole-transport lengths, organic–inorganic lead halide perovskite solar cells have attracted enormous attention recently under the urgent demands of green energy with environmental friendliness. Although various photovoltaic architectures based on alkylammonum lead halides have been fabricated and have achieved impressive power conversion efficiencies (PCEs), there are still several issues that need to be further addressed and solved properly, for example, the requirement of facile fabrication procedure, the chemical stability of perovskite films, and the environmental friendli‐ ness. Herein, we review the recent experimental progress on the external doping of hybrid perovskite devices by organics and metals, which demonstrate the tuning of optical absorption gap and the enhancement of both devices’ stability and perform‐ ance. Doping at varying layers in the perovskite films was discovered to contribute differently to the improvement of the hybrid organic–inorganic electronics. In the end, prospective was also made on the development of hybrid organic–inorganic devices.

Unveiling orbital coupling at the CoPc/Bi(111) surface by ab initio calculations and photoemission spectroscopy

The interfacial electronic structures of cobalt phthalocyanine adsorbed on a semimetal Bi(111) surface have been systematically investigated herein. Our study first indicates that the CoPc molecule is quite sensitive to the adsorption site on the relatively inert Bi(111) surface. Secondly, apparent change of the electronic structures of CoPc has been revealed upon adsorption as compared to that in the gas phase, due to the orbital coupling between the cobalt partial empty state and the surface state from the bismuth substrate and interfacial charge transfer. Interestingly, the local magnetic moment is still retained for the adsorbed CoPc molecule on the diamagnetic Bi(111) surface, which is different to that on other noble metal substrates. Analysis of the charge density difference and the Bader charge provides evident insight on the mechanism of interfacial charge transfer which is chiefly mediated by the central Co atom and the weak vdW dispersion between the π-conjugated macrocyclic ligand and the bismuth substrate, as further confirmed by experimental XPS results. In the end, our report may provide an appealing route towards the fundamental understanding and reliable engineering of interfacial interactions between magnetic and semimetal nanostructures.

Recent Progress in the Fabrication of Low Dimensional Nanostructures via Surface-Assisted Transforming and Coupling

Polymerization of functional organics into covalently cross-linked nanostructures via bottom-up approach on solid surfaces has attracted tremendous interest recently, due to its appealing potentials in fabricating novel and artificial low dimensional nanomaterials. While there are various synthetic approaches being proposed and explored, this paper reviews the recent progress of on-surface coupling strategies towards the synthesis of low dimensional nanostructures ranging from 1D nanowire to 2D network and describes their advantages and drawbacks during on-surface process and phase transformations, for example, from molecular self-assembly to on-surface polymerization. Specifically, Ullmann reaction is discussed in detail and the mechanism governing nanostructures’ transforming effect by surface treatment is exploited. In the end, it is summarized that the hierarchical polymerization combined with Ullmann coupling makes it possible to realize the selection of different synthetic pathways and phase transformations and obtain novel organometallic nanowire with metalorganic bonding.