In-Situ Cyclized Polyacrylonitrile as an Electron Selective Layer for n-i-p Perovskite Solar Cell with Enhanced Efficiency and Stability.

In situ cyclized polyacrylonitrile (CPAN) is developed to replace n-type metal oxide semiconductors (TiO2 or SnO2) as an electron selective layer (ESL) for highly efficient and stable n-i-p perovskite solar cells (PSCs). The CPAN layer is fabricated via facile in situ cyclization reaction of polyacrylonitrile (PAN) coated on a conducting glass substrate. The CPAN layer is robust and insoluble in common solvents, and possesses n-type semiconductor properties with a high electron mobility of 4.13×10-3 cm2 V-1 s-1. With the CPAN as an ESL, the PSC affords a power conversion efficiency (PCE) of 23.12 %, which is the highest for the n-i-p PSCs with organic ESLs. Moreover, the device with the CPAN layer holds superior operational stability, maintaining over 90 % of their initial efficiency after 500 h continuous light soaking. These results confirm that the CPAN layer would be a desirable low-cost and efficient ESL for n-i-p PSCs and other photoelectronic devices with high performance and stability.

Free-Rider Games for Cooperative Spectrum Sensing and Access in CIoT Networks.

With the rapid development of technologies such as wireless communications and the Internet of Things (IoT), the proliferation of IoT devices will intensify the competition for spectrum resources. The introduction of cognitive radio technology in IoT can minimize the shortage of spectrum resources. However, the open environment of cognitive IoT may involve free-riding problems. Due to the selfishness of the participants, there are usually a large number of free-riders in the system who opportunistically gain more rewards by stealing the spectrum sensing results from other participants and accessing the spectrum without spectrum sensing. However, this behavior seriously affects the fault tolerance of the system and the motivation of the participants, resulting in degrading the system's performance. Based on the energy-harvesting cognitive IoT model, this paper considers the free-riding problem of Secondary Users (SUs). Since free-riders can harvest more energy in spectrum sensing time slots, the application of energy harvesting technology will exacerbate the free-riding behavior of selfish SUs in Cooperative Spectrum Sensing (CSS). In order to prevent the low detection performance of the system due to the free-riding behavior of too many SUs, a penalty mechanism is established to stimulate SUs to sense the spectrum normally during the sensing process. In the system model with multiple primary users (PUs) and multiple SUs, each SU considers whether to free-ride and which PU's spectrum to sense and access in order to maximize its own interests. To address this issue, a two-layer game-based cooperative spectrum sensing and access method is proposed to improve spectrum utilization. Simulation results show that compared with traditional methods, the average throughput of the proposed TL-CSAG algorithm increased by 26.3% and the proposed method makes the SUs allocation more fair.

Vacuum-Assisted Thermal Annealing of CsPbI3 for Highly Stable and Efficient Inorganic Perovskite Solar Cells.

Inorganic cesium lead iodide perovskite CsPbI3 is attracting great attention as a light absorber for single or multi-junction photovoltaics due to its outstanding thermal stability and proper band gap. However, the device performance of CsPbI3 -based perovskite solar cells (PSCs) is limited by the unsatisfactory crystal quality and thus severe non-radiative recombination. Here, vacuum-assisted thermal annealing (VATA) is demonstrated as an effective approach for controlling the morphology and crystallinity of the CsPbI3 perovskite films formed from the precursors of PbI2 , CsI, and dimethylammonium iodide (DMAI). By this method, a large-area and high-quality CsPbI3 film is obtained, exhibiting a much reduced trap-state density with prolonged charge lifetime. Consequently, the solar cell efficiency is raised from 17.26 to 20.06 %, along with enhanced stability. The VATA would be an effective approach for fabricating high-performance thin-film CsPbI3 perovskite optoelectronics.

Integrated silicon nitride organic hybrid DFB laser with inkjet printed gain medium.

The provision of a coherent light source is a prerequisite for a variety of photonic integrated circuits. The integration of semiconductor laser diodes in disposable photonic devices in fields such as biosensing is, however, impeded by the competitive pricing in this application area. In this work, we demonstrate lasing of an alternative laser light source, namely an integrated hybrid organic solid-state distributed feedback laser for a silicon nitride photonic platform. The laser is optically pumped with a high power 450 nm laser diode and emits in the visible at 630 nm into a waveguide taper to reduce the cross-section to a single mode geometry. Inkjet printing of the organic gain medium enables a local, cost-effective, and flexible processing technology. The fabrication of the presented coherent light source is CMOS compatible and therefore highly interesting for co-integrated sensing platforms.

A Cation-Exchange Approach for the Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells.

Tin-based halide perovskite materials have been successfully employed in lead-free perovskite solar cells, but the overall power conversion efficiencies (PCEs) have been limited by the high carrier concentration from the facile oxidation of Sn2+ to Sn4+ . Now a chemical route is developed for fabrication of high-quality methylammonium tin iodide perovskite (MASnI3 ) films: hydrazinium tin iodide (HASnI3 ) perovskite film is first solution-deposited using presursors hydrazinium iodide (HAI) and tin iodide (SnI2 ), and then transformed into MASnI3 via a cation displacement approach. With the two-step process, a dense and uniform MASnI3 film is obtained with large grain sizes and high crystallization. Detrimental oxidation is suppressed by the hydrazine released from the film during the transformation. With the MASnI3 as light harvester, mesoporous perovskite solar cells were prepared, and a maximum power conversion efficiency (PCE) of 7.13 % is delivered with good reproducibility.

Circular fringe projection profilometry: erratum.

In this erratum, an error in Eq. (14) in our recently published Letter [Opt. Lett.41, 4951 (2016)10.1364/OL.41.004951OPLEDP0146-9592] is corrected.

Circular fringe projection profilometry.

In this Letter, a novel three-dimensional (3D) measurement method, called the circular fringe projection profilometry (CFPP), is proposed. Similar to the conventional fringe projection profilometry, CFPP also requires fringe pattern projection and capture, phase demodulation, and phase unwrapping. However, it works with a totally different mechanism. CFPP recovers the height of a point by calculating its distance to the optical center of a projector along the optical axis. This distance is calculated with the aid of the divergence angle of a projected light ray and the distance between the measured point and the optical axis. The distance between the measured point and the optical axis is detected by a camera with telecentric lenses, while the divergence angle can be calculated from the phase of a captured circular fringe pattern. The validity of CFPP is confirmed by a set of experiments.

Facile Dimension Transformation Strategy for Fabrication of Efficient and Stable CsPbI3 Perovskite Solar Cells.

All-inorganic cesium lead triiodide (CsPbI3) perovskite has received increasing attention due to its intrinsic thermal stability and suitable band gap for photovoltaic applications. However, it is difficult to deposit high-quality pure-phase CsPbI3 films using CsI and PbI2 as precursors due to the rapid nucleation and crystal growth by the solution coating method. Here, a simple cation-exchange approach is employed to fabricate all-inorganic 3D CsPbI3 perovskite, where 1D ethylammonium lead (EAPbI3) perovskite is first solution-deposited and then transformed to 3D CsPbI3 via ion exchange between EA+ and Cs+ during thermal annealing. The large space between the PbI3- skeletons in 1D EAPbI3 favors the cation interdiffusion and exchange for the formation of pure-phase 3D CsPbI3 with full compactness and high crystallinity and orientation. The resulting CsPbI3 film exhibits a low trap density of state and high charge mobility, and the perovskite solar cell shows a power-conversion efficiency of 18.2% with enhanced stability. This strategy provides an alternative and promising fabrication route for the fabrication of high-quality all-inorganic perovskite devices.

Organic-inorganic hybrid perovskite for low-cost and high-performance xerographic photoreceptors.

Solution-processable organic-inorganic hybrid perovskites are being widely investigated for many applications, including solar cells, light-emitting diodes, photodetectors, and lasers. Herein, we report, for the first time, successful fabrication of xerographic photoreceptors using methylammonium lead iodide (CH3NH3PbI3) perovskite as a light-absorbing material. With the incorporation of polyethylene glycol (PEG) into the perovskite film, the ion migration inherent to the perovskite material can be effectively suppressed, and the resulting photoreceptor exhibits a high and panchromatic photosensitivity, large surface potential, low dark decay, and high environmental resistance and electrical cycling stability. Specifically, the energies required to photodischarge one half of the initial surface potential (E 0.5) are 0.074 µJ cm-2 at 550 nm and 0.14 µJ cm-2 at 780 nm, respectively. The photosensitivites outmatch those of the conventionally used organic pigments having narrow spectral responses. Our findings inform a new generation of highly efficient and low-cost xerographic photoreceptors based on perovskite materials.

Space-time stereo analysis combining local structure and modulation features in the monogenic wavelet domain.

A multimodal cost function, based on the local multimodal image descriptors that combine local structure features (orientation, coherency) and modulation/localization information (amplitude, phase, and spatial frequency) of the monogenic wavelet transform, is proposed to estimate the time-varying disparity maps in the space-time stereo framework. The proposed cost function makes use of a constraint of local orientation, phase, and amplitude congruencies with the weighted coefficients, which are adapted to local image features and are insusceptible to level shift, scaling, and rotation and lighting invariance. Experiments on the synthetic and natural stereo sequences show the estimated results are more robust than the intensity-based sum of standard sum of squared difference cost function.

Multiscale stereo analysis based on local-color-phase congruency in the color monogenic signal framework.

A multiscale method based on local-color-phase congruency in the color monogenic signal framework is proposed to match feature points and estimate disparity maps for stereo images. As the monogenic signal is the extension of the analytic signal to gray-level images using the Dirac operator and the Laplace equation, the scale-space color monogenic signal is the extension of the monogenic signal to color images based on Clifford algebras. The local color phase, which is estimated by computing the geometric product between the color monogenic signal and a unit reference vector in red-green-blue color space, contains the color and geometric structure information and is robust against noise and brightness change. Experimental results on synthetic and natural stereo images show the performance of the proposed approach.

In Situ Deposition of CuBiS2 on Mesoporous TiO2 Film for Light Absorber in Solar Cells.

In this report, emplectite (CuBiS2) semiconductor has been deposited on mesoporous TiO2 using gas-solid reaction method. For the first time, CuCl2 and BiCl3 are solution-coated on mesoporous TiO2 films, and thereafter reacted with H2S gas in an H2S atmosphere. The CuBiS2 film is further confirmed using X-ray diffraction; thus, demonstrating the pure phase of CuBiS2. CuBiS2 film shows high spectral absorption with an energy gap (Eg) of 2.18 eV. Furthermore, devices have a structure consisting of FTO/compact-TiO2/mesoporous-TiO2/CuBiS2/P3HT/Ag have been fabricated and hence exhibit high photoresponse performance.

Methylamine-assisted growth of uniaxial-oriented perovskite thin films with millimeter-sized grains.

Defects from grain interiors and boundaries of perovskite films cause significant nonradiative recombination energy loss, and thus perovskite films with controlled crystallinity and large grains is critical for improvement of both photovoltaic performance and stability for perovskite-based solar cells. Here, a methylamine (MA0) gas-assisted crystallization method is developed for fabrication of methylammonium lead iodide (MAPbI3) perovskite films. In the process, the perovskite film is formed via controlled release of MA0 gas molecules from a liquid intermediate phase MAPbI3·xMA0. The resulting perovskite film comprises millimeter-sized grains with (110)-uniaxial crystallographic orientation, exhibiting much low trap density, long carrier lifetime, and excellent environmental stability. The corresponding perovskite solar cell exhibits a power conversion efficiency (PCE) of ~ 21.36%, which is among the highest reported for MAPbI3-based devices. This method provides important progress towards the fabrication of high-quality perovskite thin films for low-cost, highly efficient and stable perovskite solar cells.

Ion Exchange/Insertion Reactions for Fabrication of Efficient Methylammonium Tin Iodide Perovskite Solar Cells.

The low toxicity, narrow bandgaps, and high charge-carrier mobilities make tin perovskites the most promising light absorbers for low-cost perovskite solar cells (PSCs). However, the development of the Sn-based PSCs is seriously hampered by the critical issues of poor stability and low power conversion efficiency (PCE) due to the facile oxidation of Sn2+ to Sn4+ and poor film formability of the perovskite films. Herein, a synthetic strategy is developed for the fabrication of methylammonium tin iodide (MASnI3) film via ion exchange/insertion reactions between solid-state SnF2 and gaseous methylammonium iodide. In this way, the nucleation and crystallization of MASnI3 can be well controlled, and a highly uniform pinhole-free MASnI3 perovskite film is obtained. More importantly, the detrimental oxidation can be effectively suppressed in the resulting MASnI3 film due to the presence of a large amount of remaining SnF2. This high-quality perovskite film enables the realization of a PCE of 7.78%, which is among the highest values reported for the MASnI3-based solar cells. Moreover, the MASnI3 solar cells exhibit high reproducibility and good stability. This method provides new opportunities for the fabrication of low-cost and lead-free tin-based halide perovskite solar cells.

Novel TPD-based organic D-pi-A dyes for dye-sensitized solar cells.

A novel class of organic D-pi-A dyes employing a N,N,N',N'-tetraphenylbenzidine (TPD) unit as donor was designed and synthesized for dye-sensitized solar cells, which achieved a solar-to-electricity conversion efficiency (eta) of 5.63% in preliminary tests as compared to 6.42% for N3 dye under the same experimental conditions.

Slot-Waveguide Silicon Nitride Organic Hybrid Distributed Feedback Laser.

One of the major barriers for a widespread commercial uptake of silicon nitride photonic integrated circuits for cost-sensitive applications is the lack of low-cost monolithically integrated laser light sources directly emitting into single-mode waveguides. In this work, we demonstrate an optically pumped organic solid-state slot-waveguide distributed feedback laser designed for a silicon nitride organic hybrid photonic platform. Pulsed optical excitation of the gain medium is achieved by a 450 nm laser diode. The optical feedback for lasing is based on a second-order laterally coupled Bragg grating with a slot-waveguide core. Optimized material gain properties of the organic dye together with the increased modal gain of the laser mode arising from the improved overlap of the slot-waveguide geometry with the gain material enable single-mode lasing at a wavelength of 600 nm. The straightforward integration and operation with a blue laser diode leads to a cost-effective coherent light source for photonic integrated devices.

Influence of doped anions on poly(3,4-ethylenedioxythiophene) as hole conductors for iodine-free solid-state dye-sensitized solar cells.

Poly(3,4-ethylenedioxythiophene) (PEDOT) is an excellent hole-conducting polymer able to replace the liquid I(-)/I3(-) redox electrolyte in dye-sensitized solar cells (DSCs). In this work we applied the in situ photoelectropolymerization technique to synthesize PEDOT and carried out a careful analysis of the effect of different doping anions on overall solar cell performance. The anions analyzed in this work are ClO4(-), CF3SO3(-), BF4(-), and TFSI(-). The best solar cell performance was observed when the TFSI(-) anion was used. Photoelectrochemical and impedance studies reveal that the doped anions in the PEDOT hole conductor system have great influences on I-V curves, conductivity, and impedance. The optimization of these parameters allowed us to obtain an iodine-free solid-state DSC with a maximum J(sc) of 5.3 mA/cm2, V(oc) of 750 mV, and a conversion efficiency of 2.85% which is the highest efficiency obtained so far for an iodine-free solid-state DSC using PEDOT as hole-transport material.

A Novel Strategy for Scalable High-Efficiency Planar Perovskite Solar Cells with New Precursors and Cation Displacement Approach.

Methylammonium iodide (MAI) and lead iodide (PbI2 ) have been extensively employed as precursors for solution-processed MAPbI3 perovskite solar cells (PSCs). However, the MAPbI3 perovskite films directly deposited from the precursor solutions, usually suffer from poor surface coverage due to uncontrolled nucleation and crystal growth of the perovskite during the film formation, resulting in low photovoltaic conversion efficiency and poor reproducibility. Herein, propylammonium iodide and PbI2 are employed as precursors for solution deposition of propylammonium lead iodide (PAPbI3 ) perovskite film. It is found that the precursors have good film formability, enabling the deposition of a large-area and homogeneous PAPbI3 perovskite film by a scalable dip-coating technique. The dip-coated PAPbI3 film is then subjected to an organic-cation displacement reaction, resulting in MAPbI3 film with high surface coverage and crystallinity. With the MAPbI3 film as the light absorber, planar PSCs are fabricated, and stabilized power conversion efficiencies of 19.27% and 15.68% can be achieved for the devices with active areas of 0.09 and 5.02 cm2 , respectively. The technology reported here provides a robust and efficient approach to fabricate large-area and high-efficiency perovskite cells for practical application.

Sputtered Nb2O5 as an effective blocking layer at conducting glass and TiO2 interfaces in ionic liquid-based dye-sensitized solar cells.

The thin Nb(2)O(5) layer works as a remarkable blocking layer when deposited by the rf magnetron sputtering method between fluorine-doped tin oxide and a mesoporous TiO(2) layer, improving open-circuit photovoltage (V(oc)) and fill factor (FF) with power conversion efficiency over 5.5% at 1 sun irradiation of the dye-sensitized TiO(2) solar cells using ionic liquid electrolytes.