Since its first fabrication by exfoliation in 2014, phosphorene has been the focus of rapidly expanding research activities. The number of phosphorene publications has been increasing at a rate exceeding that of other two-dimensional materials. This tremendous level of excitement arises from the unique properties of phosphorene, including its puckered layer structure. With its widely tunable band gap, strong in-plane anisotropy, and high carrier mobility, phosphorene is at the center of numerous fundamental studies and applications spanning from electronic, optoelectronic, and spintronic devices to sensors, actuators, and thermoelectrics to energy conversion, and storage devices. Here, we review the most significant recent studies in the field of phosphorene research and technology. Our focus is on the synthesis and layer number determination, anisotropic properties, tuning of the band gap and related properties, strain engineering, and applications in electronics, thermoelectrics, and energy storage. The current needs and likely future research directions for phosphorene are also discussed. , there has been a quest for new two-dimensional (2D) materials aimed at fully exploring new fundamental phenomena stemming from quantum confinement and size effects. This quest has spurred new areas of research with rapid growth from both theoretical and experimental fronts aimed at technological advancements. Among recently discovered 2D materials, phosphorene is one of the most intriguing due to its exotic properties and numerous foreseeable applications.2 This review discusses recent advances in phosphorene research with special emphasis on: (i) fabrication and techniques for rapid identification of the number of layers; (ii) anisotropic behavior; (iii) band gap and property tuning; (iv) strain engineering and mechanical properties; (v) devices and applications; and (vi) future directions.2D materials composed of a single-atom-thick or a singlepolyhedral-thick layer can be grouped into diverse categories.

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Uniform polyaniline nanofibers (PANI NFs) and chemically doped sulfamic acid (SFA) PANI NFs, synthesized via template free interfacial polymerization process, were used as new counter electrodes materials for the fabrication of the highly efficient dye-sensitized solar cells (DSSCs). The PANI NFs-based fabricated DSSCs exhibited a solar-to-electricity conversion efficiency of ∼4.0%, while the SFA-doped PANI NFs-based DSSC demonstrated ∼27% improvement in the solar-to-electricity conversion efficiency. The obtained solar-to-electricity conversion efficiency for SFA-doped PANI NFs-based DSSC was 5.5% under 100 mW/cm2 (AM1.5). The enhancement in the conversion efficiency was due to the incorporation of SFA into the PANI NFs, which resulted in the higher electrocatalytic activity for the I3 −/I− redox reaction.

Vertically aligned zinc oxide (ZnO) nanorods (NRs) were grown by the low-temperature hydrothermal method on graphene oxide (GO) coated FTO substrates, where GO was directly deposited on fluorine doped tin oxide (FTO) substrates using hydrogen (H(2), 65 sccm) and methane (CH(4), 50 sccm) through hot filament chemical vapor deposition (HFCVD) technique. The vertically aligned ZnO NRs were applied as effective photoanode for the fabrication of efficient dye sensitized solar cells (DSSCs). Highly uniform ZnO NRs were grown on GO deposited FTO substrate with the average length of ∼2-4 μm and diameter of ∼200-300 nm. The possible mechanism of grown ZnO NRs clearly revealed the significant role of GO on FTO in architecting the aligned growth of ZnO NRs. The grown vertically aligned ZnO NRs possessed a typical wurtzite hexagonal crystal structure. The structural and the optical studies confirmed the formation of partial hydrogen bonding between surface functional groups of GO and ZnO NRs. A solar-to-electricity conversion efficiency of ∼2.5% was achieved by DSSC fabricated with ZnO NRs deposited on graphene oxide (GO-ZnO NRs) thin film photoanode. The presence of GO on FTO substrate expressively increased the surface area of GO-ZnO photoanode, which resulted in high dye loading as well as high light harvesting efficiency and thus ensued the increased photocurrent density and the improved performance of DSSCs.

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