ZKC

Despite the high power conversion efficiency and ease of fabrication, planar-junction organolead halide perovskite solar cells often exhibit anomalous hysteretic current–voltage (I–V) characteristics. In this work, the origin of the I–V hysteresis is studied by fine-tuning the precursor ratio of methylammonium lead iodide and thus varying the native defects in the material. It is shown that the perovskites synthesized from “PbI₂ excess,” “methylammonium iodide excess,” and “stoichiometric” precursors exhibit identical film morphology but different I–V hysteresis in a planar solar cell configuration. Through a comparative analysis on the temperature-dependent continuous and stepwise-stabilized I–V responses of the three devices, a model involving transport and trapping of the ionic native defects is proposed. The active energy of the transport process is estimated to be between 0.10 and 0.18 eV, most likely associated with the vacancy-mediated iodide ion migration. The lower activation energy of the “PbI₂ excess” and “Stoichiometric” samples indicates that the presence of methylammonium vacancies may provide a favorable pathway for the migration of iodide ions due to reduced steric hindrance. Furthermore, the slow trapping and release processes of iodide ions at the TiO₂/perovskite interface are accounted for the long time scale current decay (or raise) following a voltage change.

The origin of the current–voltage hysteresis is studied by fine-tuning the precursor ratio of methylammonium lead iodide and thus varying the native defects in the material. The lower activation energy of the “PbI₂ excess” and “stoichiometric” samples indicates that the presence of MA vacancies may provide a favorable pathway for the migration of iodide ions.

Spray coating, a simple and low-cost technique for large-scale film deposition, is employed to fabricate mesoporous titania films, which are electron-transporting layers in all-solid-state dye-sensitized solar cells (DSSCs). To optimize solar cell performance, presynthesized crystalline titania nanoparticles are introduced into the mesoporous titania films. The composite film morphology is examined with scanning electron microscopy, grazing incidence small-angle X-ray scattering, and nitrogen adsorption–desorption isotherms. The crystal phase and crystallite sizes are verified by X-ray diffraction measurements. The photovoltaic performance of all-solid-state DSSCs is investigated. The findings reveal that an optimal active layer of the all-solid-state DSSC is obtained by including 50 wt% titania nanoparticles, showing a foam-like morphology with an average pore size of 20 nm, featuring an anatase phase, and presenting a surface area of 225.2 m² g⁻¹. The optimized morphology obtained by adding 50 wt% presynthesized crystalline titania nanoparticles yields, correspondingly, the best solar cell efficiency of 2.7 ± 0.1%.

All-solid-state dye-sensitized solar cell performance is tuned by the addition of presynthesized crystalline titania nanoparticles. Films with 50 wt% nano­particles possess the network morphology best suited for poly(3-hexylthiophene) infiltration. Due to optimal crystal size and highest conductivity, the corresponding solar cells show the best photovoltaic performance.

Highly efficient hybrid multijunction solar cells are constructed with a wide-bandgap amorphous silicon for the front subcell and a low-bandgap polymer for the back subcell. Power conversion efficiencies of 11.6% and 13.2% are achieved in tandem and triple-junction configurations, respectively. The high efficiencies are enabled by deploying effective optical management and by using photoactive materials with complementary absorption.

A simple, low-cost blade-coating method is developed for the large-area fabrication of single-crystalline aligned CH₃NH₃PbI₃ microwire (MW) arrays. The solution-coating method is applicable to flexible substrates, enabling the fabrication of MW-array-based photodetectors with excellent long-term stability, flexibility, and bending durability. Integrated devices from such photodetectors demonstrate high performance for high-resolution, flexible image sensors.

5 mm-scale large FAPbI 3 single crystals and corresponding photoconductive properties are shown. The phase transition of FAPbI₃ between the α-phase and δ-phase is studied. The carrier mobility is 4.4 cm² V⁻¹ s⁻¹ with a lifetime of 484 ns in the bulk of the single crystal. Finally, photodetectors based on single-crystal FAPbI₃ are demonstrated.

Large-aspect-ratio composite nanofibers with interior hierarchical interfaces are employed to break the adverse coupling of electric displacement and breakdown strength in flexible poly(vinylidene fluoride-hexafluoropropylene) nanocomposite films, a small loading of 3 vol% BaTiO₃@TiO₂ nanofibers gives rise to the highestenergy density (≈31.2 J cm⁻³) ever achieved in polymer nanocomposites dielectrics.

The power conversion efficiency potential of eight high-performance polymer–fullerene blends is investigated. All studied absorbers show the typical organic solar cell losses limiting their performance to ≈13%.

Flexible electrochemical energy storage (FEES) devices have received great attention as a promising power source for the emerging field of flexible and wearable electronic devices. Carbon nanotubes (CNTs) and graphene have many excellent properties that make them ideally suited for use in FEES devices. A brief definition of FEES devices is provided, followed by a detailed overview of various structural models for achieving different FEES devices. The latest research developments on the use of CNTs and graphene in FEES devices are summarized. Finally, future prospects and important research directions in the areas of CNT- and graphene-based flexible electrode synthesis and device integration are discussed.

Carbon nanotubes (CNTs) and graphene for flexible electrochemical energy storage are reviewed. A definition of flexible devices, followed by an overview of the various structural models for achieving different flexible devices is provided. The use of CNTs and graphene in flexible devices is summarized. Future prospects and important research directions of flexible electrode are introduced.