The key progress in the development of solar cells based on mixed organic-inorganic halide perovskite was reviewed. Perovskite solar cells (PSCs) have developed rapidly and achieved highest efficiency exceeding 20% in these years. The origin, working principle and fabrication technology of PSCs are stated, and several promising methods to realize the industrialization of the solar cell modules have been put forward. Meanwhile, two main problems existing in PSCs have been pointed out, hysteresis in the photocurrent density-voltage measurement and the instability of perovskite, which have impacted the application of PSCs seriously. Efforts and study in order to solve these problems are also listed. The fundamental mechanism still needs further investigation so as to improve the performance of PSCs and realize their large-scale application eventually.

Advancing lead halide perovskite solar cells to photovoltaic application requires reproducible and stable devices using low-cost fabricating techniques. Here a device structure is developed with organic network uniformly incorporated into the organic/inorganic hybrid perovskite film by one-step solution-processing strategy, which significantly improves the photovoltaic performance and long-term stability of planar type perovskite solar cells. The organic network is composed with PCBM and PEG. Therein, a long-chain insulating polymer PEG acts as a network to improve film morphology, as well as device stability. The fullerene derivative PCBM in the composite forms conducting channels to assist the charge transfer and transport in perovskite film. Besides, PCBM in perovskite film can passivate trap states on grain boundaries, so that the photocurrent hysteresis of the device is suppressed significantly. This organic composite network enhances the photovoltaic performance of perovskite solar cells with maximum power conversion efficiency of 17.1%, showing long duration at the maximum power point tracking up to ~170 min. This low-cost organic network demonstrates a promising method for industry-scale fabrication of the organic/inorganic hybrid perovskite solar technology.

Ion migration has been regarded as the major cause of photocurrent hysteresis. Here we use photoluminescence (PL) and optical images, combined with Galvanostatic measurement, to detect the ionic motion. We observe an irreversible PL and optical transmittance change after electric poling. By comparing a neat perovskite film with the sample coated by poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we found that PCBM effectively inhibits ionic motion near the surface of the perovskite.We further evidenced the donor–acceptor complex formed between PCBM and perovskite, implying the mechanism of inhibited ion migration by PCBM. We close by demonstrating that PCBM can also be introduced on the top of perovskite fim in an n–i–p TiO2 planar structure, to achieve an average 14% steady-state output over 2.3 × 105 s (∼64 h). This work highlights the importance of inhibiting ionic motion in perovskite solar cells.

Advancing of the lead halide perovskite solar cells towards photovoltaic market demands large-scale devices of high-power conversion efficiency, high reproducibility and stability via low-cost fabrication technology, and in particular resistance to humid environment for long-time operation. Here we achieve uniform perovskite film based on a novel polymer-scaffold architecture via a mild-temperature process. These solar cells exhibit efficiency of up to ∼ 16% with small variation. The unencapsulated devices retain high output for up to 300 h in highly humid environment (70% relative humidity). Moreover, they show strong humidity resistant and self-healing behaviour, recovering rapidly after removing from water vapour. Not only the film can self-heal in this case, but the corresponding devices can present power conversion efficiency recovery after the water vapour is removed. Our work demonstrates the value of cheap, long chain and hygroscopic polymer scaffold in perovskite solar cells towards commercialization.

The metal-insulator-semiconductor (MIS) structure is applied to perovskite solar cells, in which the traditional compact layer TiO2 is replaced by Al2O3 as the hole blocking material to realize an all-low-temperature process. Flexible devices based on this structure are also realized with excellent flexibility, which hold 85% of their initial efficiency after bending 100 times.

This paper proposed a new architecture design for nanowire-based quantum-dot-sensitized solar cells to improve the photovoltaic performance. Microstructured rough substrate was used to increase the surface area of the photoanode without influence on charge carrier transport in the system. Compared to conventional devices, the short circuit current density and power conversion efficiency were enhanced by 50%. And the technology can be widely used in the photoelectrochemical (PEC) field, and it can be combined with other hierarchical nanostructures.

Hybrid lead-halide perovskite solar cells (PSCs) have become the hot spot in photovoltaic domain since 2012. Although perovskite solar cells exhibit high power conversion efficiencies (PCE), some unsolved issues remain in the measurement of device performance, especially the abnormal hysteresis in current-voltage scan. The hysteresis phenomena result in the overstatement of the performance of PSCs during backward scan, which starts from the bias higher than open voltage and sweep to voltage below zero. In steady output, the stabilised PCE is lower than the dynamic outcome, such as the maximum power point in the I-V curve. The origin of this abnormal hysteresis is under debate. Here, we introduced a model to explain the dependence of I-V measurements on scan history. According to computational simulations using semiconductor transport theories, we found that the experimental results were consistent with the model based on the polarisation of perovskite materials. The bias-induced polarisation affects both the heterojunction resistance and the magnitude of light-generated current. By analysing current results, we supports the view that polarisation is caused by internal ion migration rather than ferroelectricity.

An “all-in-one” mesh typed integrated energy unit is developed which converts solar energy to electric energy and stores it simultaneously. The entire integrated device operates in uniform electrolyte system which contains 0.8 M Na2S, 0.8 M S, and 2 M KCl. A double-sided mesh electrode coated with Cu2S film and carbon nanoparticles is shared by both energy conversion and storage sections. The device we fabricated can realize the co-operation of the energy conversion and storage sections effectively by taking advantages of the mono electrolyte system and the shared double-sided mesh-typed electrode. These properties are beneficial to assembly, miniaturization, and integration of a self-powered system for portable microelectronic devices.

Reducing the electronic contact resistance at the interfaces of nanostructured materials is a major goal for many kinds of planar and three dimensional devices. In this work, we develop a method to enhance the electronic transport at rough interfaces by inserting a two dimensional flexible and conductive graphene sheet. We observe that an ultra-thin graphene layer with a thickness of 0.35 nm can remarkably reduce the roughness of a sample in a factor of 40%, avoiding the use of thick coatings, leading to a more homogeneous current flow, and extraordinarily increasing the total current compared to the graphene-free counterpart. Due to its simplicity and performance enhancement, this methodology can be of interest to many interface and device designers.

The power conversion efficiency of CH3NH3PbX3 (X=I,Br,Cl) perovskite solar cells has been developed rapidly from 6.5 to 20% within 3 years. The anomalous hysteresis found in I−V measurements of perovskite solar cells can cause an inaccurate estimation of the efficiency. We attribute the phenomena to the ferroelectric effect and build a model based on the ferroelectric diode to explain it. We also will demonstrate a novel self-healing behavior under vapor spray of an improved type of perovskite solar cells.

A simple, low cost and efficient flexible sandwich structure supercapacitor is developed using stainless steel mesh as electrode and commercial pen ink as active material by means of a facile and environment-friendly process. The devices show good capacitance performance, such as high specific capacitance, low inner resistance, high energy density and power density, and ultra-long cycle lifetime. The use of mesh and pen ink significantly lower the fabrication cost of supercapacitors which feature light weight and highly flexible characteristics. The stable and robust ink film on mesh electrode makes it fully compatible for conventional carbon material modification to fabricate pseudocapacitors. The comparison between the mesh-type and plate-type electrode supercapacitors certificates the good electrochemical performance of pen ink film and the advantages of mesh-type electrode. The simple dip-coating method is easily scalable for making large-scale flexible and wearable energy storage devices based on mesh and carbon ink. (C) 2014 Elsevier Ltd. All rights reserved.

Highly-flexible, ITO-free dye-sensitized solar cells (DSSCs) are fabricated in a simple, all-solution-based, facile, and controllable way. A double mesh structure is applied to DSSCs, and the design principles, especially scale parameters, are analyzed delicately to ensure the power conversion efficiency and mechanical flexibility of the device. The good flexibility of mesh-based DSSCs is verified by systematic bending tests compared to conventional flexible DSSCs based on PET/ITO or metal foil substrates. Commercial carbon ink is used as a counter electrode material, and it is proved to be low-cost and efficient. The double mesh structure design provides an attractive strategy toward the development of flexible and wearable electrochemical energy supplies.

The power conversion efficiency (PCE) of CH3NH3PbX3 (X = I, Br, Cl) perovskite solar cells has been developed rapidly from 6.5 to 18% within 3 years. However, the anomalous hysteresis found in I-V measurements can cause an inaccurate estimation of the efficiency. We attribute the phenomena to the ferroelectric effect and build a model based on the ferroelectric diode to explain it. The ferroelectric effect of CH3NH3PbI3-xClx is strongly suggested by characterization methods and the E-P (electrical field-polarization) loop. The hysteresis in I-V curves is found to greatly depend on the scan range as well as the velocity, which is well explained by the ferroelectric diode model. We also find that the current signals show exponential decay in ∼10 s under prolonged stepwise measurements, and the anomalous hysteresis disappears using these stabilized current values. The experimental results accord well with the model based on ferroelectric properties and prove that prolonged stepwise measurement is an effective way to evaluate the real efficiency of perovskite solar cells. Most importantly, this work provides a meaningful perspective that the ferroelectric effect (if it really exists) should be paid special attention in the optimization of perovskite solar cells.

The morphology of nanospheres is crucial for designing the nanofabrication in the nanosphere lithography. Here, by plasma etching, the controllable tailoring of the nanosphere is realized and its morphology dependence on the initial shape, microscopic roughness, and the etching conditions is investigated quantitatively. The results show that the shape evolution strongly depends on the etching gas, power, and process duration. Particularly, the aspect ratio (diameter/height) significantly increases with violent etching, turning the spherical shape into tiny ellipsoidal nanoparticles. The findings are practical to the protocol of non-uniform etching of nanoobjects and provide the useful design tool for the device fabrication at nanoscale.

Flexible and transparent power sources are highly desirable in realizing next-generation all-in-one bendable, implantable, and wearable electronic systems. The developed power sources are either flexible but opaque or semitransparent but lack of flexibility. Therefore, there is increasing recognition of the need for a new concept of electrochemical device structure design that allows both high flexibility and transparency. In this paper, we present a new concept for electrochemical device design--a two-dimensional planar comb-teeth architecture on PET substrate--to achieve both high mechanical flexibility and light transparency. Two types of prototypes--dye-sensitized solar cells and supercapacitors--have been fabricated as planar devices and demonstrated excellent device performance, such as good light transparency, excellent flexibility, outstanding multiple large bending tolerance, light weight, effective prevention of short circuits during bending, and high device integration with up-date microelectronics, compared to conventional sandwich structure devices. Our planar design provides an attractive strategy toward the development of flexible, semitransparent electrochemical devices for fully all-in-one elegant and wearable energy management.

Large scale, uniform single-layer graphene was transferred onto well-aligned ZnO nanowire arrays to produce high density nanoscale protrusions within graphene for efficient field emission. Polymethyl methacrylate (PMMA) was used as a supporting layer to provide a quasi-flat surface for graphene transfer. Highly efficient (maximum current density of ∼500 μA/cm2) and stable field emission with low turn-on fields (5.4 V/μm) was observed due to highly localized electric field, which is much better than those without using PMMA. F-N plot showed an unique up-bending feature of single-layer graphene. Our approach provides an efficient way to produce high quality single-layer graphene field emitters.

Transparent, double-sided, flexible, ITO-free dye-sensitized solar cells (DSSCs) are fabricated in a simple, facile, and controllable way. Highly ordered, high-crystal-quality, high-density ZnO nanowire arrays are radially grown on stainless steel, Au, Ag, and Cu microwires, which serve as working electrodes. Pt wires serve as the counter electrodes. Two metal wires are encased in electrolyte between two poly(ethylene terephthalate) (PET) films (or polydimethylsiloxane (PDMS) films) to render the device both flexible and highly transparent. The effect of the dye thickness on the photovoltaic performance of the DSSCs as a function of dye-loading time is investigated systematically. Shorter dye-loading times lead to thinner dye layers and better device performance. A dye-loading time of 20 min results in the best device performance. An oxidation treatment of the metal wires is developed effectively to avoid the galvanic-battery effect found in the experiment, which is crucial for real applications of double-metal-wire DSSC configurations. The device shows very good transparency and can increase sunlight use efficiency through two-sided illumination. The double-wire DSSCs remain stable for a long period of time and can be bent at large angles, up to 107 degrees, reversibly, without any loss of performance. The double-wire-PET, planar solar-cell configuration can be used as window stickers and can be readily realized for large-area-weave roll-to-roll processing.

We experimentally demonstrate the dependence of plasmonic resonant properties on cavity height in open circular cylinder nanocavities as a result of a strong three-dimensional confinement of the electromagnetic field, which shows a new way to tailor the dispersion of surface plasmon polaritons in cavities. The azimuthal and the axial symmetric plasmonic mode patterns are directly observed at resonant wavelengths using cathodoluminescence spectroscopy. Plasmonic modes and optical vertical cavity modes can be simultaneously excited and can coexist in a nanocavity with sufficient height. The highest quality factor, which is up to 73, is obtained in a 500 nm high cavity. The smallest mode volume is only 0.031 λ(SPP)(3), and the corresponding Purcell factor is 71. Open nanocavities provide space for the interaction between an optical emitter and a confined electromagnetic field. Many applications can be expected, such as plasmonic light-emitting devices and nanolasers.