[en] This paper reports the doping effect of cholesteric liquid crystal 3 β -Hydroxy-5-cholestene 3-oleate on polymer solar cells composed of the poly 3-hexyl thiophene and the fullerene derivative. With a doping ratio of 0.3 wt%, the device achieves an ideal improvement on the shunt resistor and the fill factor. Compared with the reference cell, the power conversion efficiency of the doped cell is improved 24%. The photoelectric measurement and the active layer characterization indicate that the self-assembly liquid crystal can improve the film crystallization and reduce the membrane defect. (special topic)

[en] The structural, optical, and electrical characteristics of zinc sulfide (ZnS)/Ag/ZnS (ZAZ) multilayer films prepared by ion beam assisted deposition on k9 glass have been investigated as a function of Ag layer thickness. The characteristics of ZAZ multilayer are significantly improved up insertion of optimal Ag thickness between ZnS layers. The results show that due to bombardment of Ar ion beam, distinct Ag islands evolve into continuous Ag films at a thin Ag thickness of about 4 nm. The thinner Ag film as a thickness of 2 nm leads to high sheet resistance and low transmittance for the interface scattering induced by the Ag islands or noncontinuous films; and when the Ag thickness is over 4 nm, the ZAZ multilayer exhibits a remarkably reduced sheet resistance between 7-80 Ω/sq for the increase in carrier concentration and mobility of Ag layer, and a high transmittance over 90% for the interference phenomena of multilayers and low absorption and surface scattering of Ag layer. The ZAZ multilayer with 14 nm Ag film has a figure of merit up to 6.32x10^-2 Ω^-1, an average transmittance over 92% and a sheet resistance of 7.1 Ω/sq. The results suggest that ZAZ film has better optoelectrical properties than conditional indium tin oxide single layer.

[en] This paper presents a novel technique for developing new structures on a Si substrate used in micro electro mechanical systems. The technique does not require any compensating structure for the fabrication of circle-like 3D microstructures, as reported in the literature. We design a two-step wet etching process and the results show that the application of the technique can lead to an optimal etching process in a more effective manner for the realization of circle-like 3D microstructures, based on a mixture of 5M KOH solution with 20% by volume isopropyl alcohol (IPA) etching at 80 °C for 80 min and then isotropic etching in HF-HNO₃ at room temperature for 3 min

[en] The charge transfer rate coefficients for reactions of Sc³⁺ with N₂ and H₂ have been measured at the mean collision energy of 4.2 eV. The rate coefficients are derived from the decay rate of ion signals by using ion storage in a radio frequency ion trap. The rate coefficients are 8.18(0.18) x 10^-10 cm³·s^-1 at T_equiv ≅ 1.26 x 10⁴ K for Sc³⁺ with N₂ and 1.44(0.39) x 10^-9 cm³·s^-1 at T_equiv ≅ 1.67 x 10³ K for Sc³⁺ with H₂, respectively. Both results are comparable with the Langevin rate coefficients

[en] Solution-processable hybrid perovskite solar cells offer potential in the photovoltaic field due to their low-cost fabrication and high efficiency. However, an undesirable current–voltage (J-V) hysteresis hampers the applications of perovskite solar cells. In particular, for the inverted device, the understandings for J-V hysteresis origination are not uniform, and the inverted hysteresis phenomenon has been further complicated the hysteresis behavior. In this report, an external bias precondition method is adopted to unveil the origin of the inverted hysteresis. The results indicate that the extents of inverted hysteresis are very much dependent on the bias direction of the precondition. To further unveil the effect of the precondition on inverted hysteresis, the microscopic J-V hysteresis was also observed by using conductive atomic force microscopy (c-AFM) measurements. The results indicate that ion migration and accumulation slowly built up at the grain boundaries of the perovskite film when repeating the scan using c-AFM. Furthermore, the transient characteristics based on capacity-frequency plots and open-circuit voltage decay further identify the presence of difference for the different bias preconditions on the device, because the different bias precondition could induce different directions of ions migration and accumulation. These observations are surprising; it can be further identified that the inverted hysteresis originates from the ionic migration and accumulation, and the grain boundary is as the channel of ionic migration and accumulation. Therefore, the grain boundary plays an important role on the hysteresis effect, and preparation of large-grain or single-crystal perovskite films is the way to reduce the hysteresis effect. (paper)

[en] The inverted-planar bulk heterojunction perovskite solar cells were fabricated by incorporating nanoparticle MoO_x into the CH₃NH₃PbI_3−xCl_x perovskite active layers. The results showed that the device performances had been significantly improved, mainly reflected the enhancement of the open-circuit voltage from an average of 0.895 V to 0.959 V. This should be attributed to formation of bulk heterojunctions that can effectively separate and extract the carrier, and reduce carrier recombination. In addition, the conductive atomic force microscopy spectroscopy verified that the surface current of the perovskite-MoO_x is larger than that of the pure perovskite film. The relationship between capacitance and frequency was tested and indirectly proved that bulk heterojunctions can rapidly separate the carriers. The ultrafast transient absorption spectroscopy measurements provided a reasonable explanation for the MoO_x-induced rapidly separating of the carriers. Our research illustrates the application potential of bulk heterojunctions in the perovskite solar cells through doping the MoO_x inorganic materials into the perovskite active layer, as well as further consolidates the role of bulk heterojunctions in perovskite active layer. (paper)

[en] In this paper, we investigate how interface-induced polarization affects the photovoltaic performance of hybrid perovskite solar cell (PSC) devices. The polarization of the hole transport layer (HTL) is regulated through incorporating metallic-like MoO_x into PEDOT:PSS. The common MoO₃ doped into PEDOT:PSS is used as a reference, and the device that used PEDOT:PSS-MoO_x as the HTL shows an enhanced J _sc and FF compared to the reference device. The open-circuit photovoltage decay and impedance spectroscopy measurements indicate that trap-assisted recombination is effectively suppressed at the interface between the hybrid perovskite and the PEDOT:PSS-MoO_x HTL, while severe trap assisted recombination takes place at the perovskite/PEDOT:PSS and perovskite/PEDOT:PSS-MoO₃ interface. We attribute these experimental findings to the fact that the incorporation of metallic-like Mo⁵⁺ into PEDOT:PSS enhances the conductivity of HTL and the interface polarization between PEDTOT:PSS layer and perovskite, which helps to induce an interface polarization electric field to facilitate separation of charges and screen the recombination between the traps and free charges. (paper)

[en] The experimental investigation and thermodynamic assessment of the Al-Ca-Y ternary system were carried out in this work. The isothermal section of the Al-Ca-Y ternary system at 673 K and 873 K was determined by using equilibrated alloys, combined with scanning electron microscopy, electron probe micro-analysis and powder X-ray diffractometry. Phase transition temperatures were measured by differential scanning calorimetry analysis. A certain range of solubility was detected between Al${}_2$Ca and Al${}_2$Y in this work, the maximum solid solubility of Y in Al${}_2$Ca was 11.9 at.% and that of Ca in Al${}_2$Y was 12.6 at.%. According to the thermodynamic data of binary systems in the literature and the ternary experimental data from this work and the literature, the Al-Ca-Y ternary system was optimized and a set of self-consistent thermodynamic parameters was obtained. Calculated phase equilibria were consistent with the experimental results.

[en] A ferroelectric field effect in the bulk heterojunction was found when an external electric field (EEF) was applied on the active layer of polymer solar cells (PSCs) during the annealing process of the active layer spin-coated with poly(3-hexylthiophene):[6,6]-phenyl-C₆₁ butyric acid methyl ester. For one direction field, the short circuit current density of PSCs was improved from 7.2 to 8.0 mA/cm², the power conversion efficiency increased from 2.4% to 2.8%, and the incident photon-to-current conversion efficiency increased from 42% to 49% corresponding to the different EEF magnitude. For an opposite direction field, the applied EEF brought a minus effect on the performance mentioned above. EEF treatment can orientate molecular ordering of the polymer, and change the morphology of the active layer. The authors suggest a explanation that the ferroelectric field has been built in the active layer, and therefore it plays a key role in PSCs system. A needle-like surface morphology of the active film was also discussed.

[en] The influencing factors on the current–voltage (I–V) characteristics of organic static induction transistors (OSITs) are complicated and usually the underneath physical mechanism depends on many parameters. In this paper, firstly we come up with a typical OSIT model and summarize its theoretical equations to the I–V curves of pentacene-based OSIT ITO(Source)/Pentacene/ Al(Gate)/Pentacene/Au(Drain) under both negative drain–source voltage and gate voltage (V _G), and the influence of contact resistance on OSITs is investigated. Our simulation showed that the injection barriers, the depletion layer and the gate controlling reduce when OSIT approaches the space-charge-limited current mode by decreasing the negative V _G, which confirms our previous supposal that the contact resistance at the interfaces of Al inter-gate electrode and at the two injection electrodes reduces after keeping the device for a long-enough time. Also, our simulating equations can be applied to other organic based OSITs under positive both V _DS and V _G. (paper)