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A smelting multiple recrystallization strategy and its effects on the morphology, composition, and defects of CsPbBrI2 film were investigated. An optimal number (n = 2) of recrystallization cycles improved the crystallinity and phase purity, minimized the grain boundaries, and optimized the crystal structure, yielding a high-quality perovskite film with significantly reduced defects density. The corresponding photovoltaic devices exhibited a champion efficiency of 16.02% under AM 1.5 G illumination and presented an even higher indoor efficiency of 33.50% under an LED (2956 K, Pin: 334.41 μW/cm2). This recrystallization method offers a promising strategy for developing high-performance indoor and outdoor photovoltaics. Direct recrystallization in the cells was also explored to achieve enhanced stability and longer lifetime in humid conditions.

Over the years, the efficiency of inorganic perovskite solar cells (PSCs) has increased at an unprecedented pace. However, energy loss in the device has limited a further increase in efficiency and commercialization. In this work, we used (NH4)2C2O4·H2O to treat CsPbBrI2 perovskite film during spin-coating. The CsPbBrI2 underwent secondary crystallization to form high quality films with micrometer-scale and low trap density. (NH4)2C2O4·H2O treatment promoted charge transfer capacity and reduced the ideal factor. It also dropped the energy loss from 0.80 to 0.64 eV. The resulting device delivered a power conversion efficiency (PCE) of 16.55% with an open-circuit voltage (Voc) of 1.24 V, which are largely improved compared with the reference device which exhibited a PCE of 13.27% and a Voc of 1.10 V. In addition, the optimized treated device presented a record indoor PCE of 28.48% under a fluorescent lamp of 1000 lux, better than that of the reference device (19.05%).

The market's increasing demand for portable electronic products has made the research in flexible devices very attractive. Flexible solar cells are one of the most eye-catching devices in the field of flexible photovoltaic devices. And the perovskite material has become a powerful candidate material for manufacturing flexible solar cells due to its excellent optical properties, low price and the ability to tolerate more stress accumulation. However, as an active layer, the perovskite film still faces the issue that cracks are easily generated when bending and encountering temperature changes for the limited flexibility. There are many factors that affect the mechanical stability of the perovskite layer: the characteristics of the material itself, the influence of the other layers in the device and the presence or absence of a protective layer. This work reviews some reported strategies of improving the perovskite bending durability, classifies them according to the influencing factors mentioned above, and describes them in detail respectively.

Compared with the rapid development of red and green perovskite light-emitting diodes (PeLEDs), the improvement of the device performance is urgent for blue PeLEDs. Herein, we developed a creative method to incorporate Cl- into quasi-2D perovskite films via dynamic processing, by mixing two main strategies of mixed-Cl/Br perovskites and quasi-2D perovskites. With methylammonium chloride (MACl) treating the perovskite film, the devices presented excellent spectral stability owing to the effective suppression of non-radiative recombination. Consequently, CsPbBr3 : PEABr-based PeLEDs exhibited a maximum external quantum efficiency of 1.74% with a bright luminance of 537 cd m−2. The redshift of the emitting luminescence (EL) peak was no more than 2 nm around 477 nm. The findings in this work will help develop other new routes for pure blue PeLEDs with ideal spectral stability.

Defects easily form in organic-inorganic hybrid perovskite (CH3NH3PbX3) absorber layers acting as recombination centers which reduce the performance of solar cells. Therefore, defect passivation is an efficient method to improve the performance of solar cells. Herein, ethylamine alcohol chlorides is introduced into perovskite films to passivate defects. The hydroxyl group and ammonium group in ethylamine alcohol chlorides can interact with halogen in MAPbIxCl3-x to form hydrogen bonds suppressing ion migration. In addition, the crosslinking neighbouring perovskite grains through hydrogen bonds can also improve the perovskite grain size and film coverage. The data demonstrate that the obvious reduction of the defect concentration via defect passivation contributes to an enhancement of the open-circuit voltage from 0.87 V to 0.92 V and the device efficiency from 14.52% to 16.97%.

A light-emitting organic solar cell (LE-OSC) with electroluminescence (EL) and photovoltaic (PV) properties is successfully fabricated by connecting the EL and PV units using a MoO(3):Al co-evaporation interfacial layer, which has suitable work function and good transmittance. PV and EL units are fabricated based on poly(3-hexylthiophene) (P3HT)-indene-C(60) bisadduct (IC(60)BA) blends, and 4,4′-bis (N-carbazolyl) biphenyl-factris (2-phenylpyridine) iridium (Ir(ppy)(3)), respectively. The work function and the transmittance of the MoO(3):Al co-evaporation are measured and adjusted by the ultraviolet photoelectron spectroscopy and the optical spectrophotometer to obtain the better bi-functional device performance. The forward- and reverse-biased current density-voltage characteristics in dark and under illumination are evaluated to better understand the operational mechanism of the LE-OSCs. A maximum luminance of 1550 cd/m(2) under forward bias and a power conversion efficiency of 0.24% under illumination (100 mW/cm(2)) are achieved in optimized LE-OSCs. The proposed device structure is expected to provide valuable information in the film conditions for understanding the polymer blends internal conditions and meliorating the film qualities. [Image: see text]

Interface strains and lattice distortion are inevitable issues during perovskite crystallization. Silane as a coupling agent is a popular connector to enhance the compatibility between inorganic and organic materials in semiconductor devices. Herein, a protonated amine silane coupling agent (PASCA-Br) interlayer between TiO2 and perovskite layers is adopted to directionally grasp both of them by forming the structural component of a lattice unit. The pillowy alkyl ammonium bromide terminals at the upper side of the interlayer provide well-matched growth sites for the perovskite, leading to mitigated interface strain and ensuing lattice distortion; meanwhile, its superior chemical compatibility presents an ideal effect on healing the under-coordinated Pb atoms and halogen vacancies of bare perovskite crystals. The PASCA-Br interlayer also serves as a mechanical buffer layer, inducing less cracked perovskite film when bending. The developed molecular-level flexible interlayer provides a promising interfacial engineering for perovskite solar cells and their flexible application.

Serious issues such as easy-oxidation of Sn2+, fast crystallization rate and high defect density are still existing in tin perovskites to restrain their photovoltaic performance. Herein, a strategy of bottom passivation by potassium thiocyanate (KSCN) has been developed in FA0.75MA0.25SnBrI2-based perovskite solar cells. KSCN interlayer exhibited multifunctional roles in aligning energy levels, assisting perovskite crystallization and promoting charge transport. The resulting champion device delivered superior power conversion efficiency (PCE) as high as 11.17% under AM 1.5G illumination. It is worth noting that the champion indoor photovoltaics efficiency under 2956 K@1062 lux (334.41 μW/cm2) illumination could approach 17.57%, which is the highest PCE for tin perovskite photovoltaics to our knowledge. The outstanding indoor performance demonstrates the huge application potential of eco-friendly tin perovskites.

Wearable devices are mainly based on plastic substrates, such as polyethylene terephthalate and polyethylene naphthalate, which causes environmental pollution after use due to the long decomposition periods. This work reports on the fabrication of a biodegradable and biocompatible transparent conductive electrode derived from bamboo for flexible perovskite solar cells. The conductive bioelectrode exhibits extremely flexible and light-weight properties. After bending 3000 times at a 4 mm curvature radius or even undergoing a crumpling test, it still shows excellent electrical performance and negligible decay. The performance of the bamboo-based bioelectrode perovskite solar cell exhibits a record power conversion efficiency (PCE) of 11.68%, showing the highest efficiency among all reported biomass-based perovskite solar cells. It is remarkable that this flexible device has a highly bendable mechanical stability, maintaining over 70% of its original PCE during 1000 bending cycles at a 4 mm curvature radius. This work paves the way for perovskite solar cells toward comfortable and environmentally friendly wearable devices.

Semiconductor nanomaterials with controlled morphologies and architectures are of critical importance for high-performance optoelectronic devices. However, the fabrication of such nanomaterials on polymer-based flexible electrodes is particularly challenging due to degradation of the flexible electrodes at a high temperature. Here we report the fabrication of nickel oxide nanopillar arrays (NiO x NaPAs) on a flexible electrode by vapor deposition, which enables highly efficient perovskite solar cells (PSCs). The NiO x NaPAs exhibit an enhanced light transmittance for light harvesting, prohibit exciton recombination, promote irradiation-generated hole transport and collection, and facilitate the formation of large perovskite grains. These advantageous features result in a high efficiency of 20% and 17% for the rigid and flexible PSCs, respectively. Additionally, the NaPAs show no cracking after 500 times of bending, consistent with the mechanic simulation results. This robust fabrication opens a new opportunity for the fabrication of a large area of high-performance flexible optoelectronic devices.

Poly(3,4-ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is a widely utilized hole-transporting material (HTM) in planar photovoltaic devices, such as organic solar cells (OSCs) and perovskite solar cells (PSCs). However, the hygroscopic nature of PEDOT:PSS aqueous dispersions may restrict their future application. Therefore, it is necessary to develop other effective and stable HTMs to achieve high-performance photovoltaic devices. Herein, we demonstrate a facile route to deposit solution-processed MoO3, GeO2, V2O5 and CrO3 thin films as hole-transporting layers by directly dissolving their commercial powders in deionized water. Among these, the solution-processed V2O5 (sV2O5) film exhibited the highest work function of 5.2 eV, and the best hydrophobicity, with a contact angle of 77.2°. The sV2O5-based OSCs and PSCs presented power conversion efficiencies (PCEs) of 8.36% and 14.13%, respectively. Notably, the PEDOT:PSS V2O5 composite HTM based device obtained a maximum PCE of 18.03% with a Voc exceeding 1.0 V. These aqueous-solution-processed HTMs have potential applications in green and low-cost photovoltaic devices by virtue of their simple and ecofriendly preparations.

Solar energy is considered as one of the most promising green energy due to clean, safe, long life, and renewable advantages. Solar cell is an electrical device that converts solar energy directly into electric power on the basis of photovoltaic effect. Fritts built the first solar cell in 1883. Although the initial efficiency was only 1%, it has been exciting to know that the power conversion efficiency of solar cells is endlessly improved since it was reported. Up to now, the efficiency of commercial silicon solar cell is between 10%–18%. The latest research shows that the best efficiency of perovskite solar cell has been improved to be over 20% within several years. As it is well known, the maximum power conversion efficiency of single-junction solar cells are only around 33% according to the Shockley- Queisser limit. With the development of new materials and high technologies, one issue is emerging: What is the ultimate efficiency of solar cells? The highest efficiency of solar cell is possible to break the Schockley-Queisser limit? How to further enhance the efficiency of solar cell? All the questions are hard to answer at present. Surrounding these concerns, this article presents a brief review about the efficiency limits of different solar cells. It might help to understand the ultimate efficiency of solar cells. The details address the basic principle, advantages and disadvantages of single-junction, multi-junction and other new concept solar cells regarding the power conversion efficiency. The review also includes the solar cell materials involving silicon, compound, perovskite, quantum dot, hybrid materials, etc. Finally, we look ahead into the prospect of new concept solar cells and the maximum power conversion efficiency.

Organic-inorganic metal halide perovskites have drawn the interest of scientific community due to their suitable optoelectronic properties and high solar cell efficiency. In this report, we demonstrated, for the first time, the application of Cs2CO3 - doped TiO2 as an efficient electron-transporting layer (ETL) in PSCs. Remarkably, the optimized Cs2CO3-doped TiO2 films exhibited improved wetting properties which assisted the deposition of perovskite films and improved the TiO2/perovskite interface by lowering the work function. With X-ray diffraction studies, better crystalline of the perovskite films could be found in the doped devices. Solar cells prepared with the Cs2CO3-doped TiO2 as ETL resulted in a 19% efficiency performance and improved stability.

Interface engineering is an efficient method for improving the performance of planar perovskite solar cells (PSCs). In this paper, the performance of PSCs was improved significantly by introducing 4,7-diphenyl-1,10-phenanthroline (Bphen) doped with bis(2-methyldibenzo-[f,h]quinoxaline) (Ir(MDQ)2(acac)) to modify the interface between perovskite (CH3NH3PbI3−xClx)/PCBM (phenyl-C61-butyric acid methyl ester) and an Ag electrode. The power conversion efficiency (PCE) was enhanced up to 15.87%, compared with 10.77% for the reference device without interlayer modification. It was found that the enhanced PCE was attributed to the better interface contact between the perovskite and Ag cathode. A suitable interface roughness is beneficial for reducing the leakage current and the probability of carrier recombination, resulting in an enhanced fill factor and thus improved device efficiency.

A new three-armed imidazolium phenoxy ionic liquid (TIPIL) has been successfully designed, synthesized and characterized. The thermal property, amorphous feature and ionic conductivity of TIPIL were also investigated. 1-Ethyl-3-methylimidazolium iodide (EMII), a typical ionic conductor, could be effectively inhibited from crystallization by TIPIL, which has been characterized by several testing. Thus, as a crystal growth inhibitor, TIPIL was used into EMII based solid-state dye-sensitized solar cells (ssDSSCs). Compared with the reference device, the DSSC containing TIPIL showed improved photovoltaic conversion efficiency up to 5.37%, and displayed excellent long-term stability. These results provide us a feasible method to explore new crystal growth inhibitors for ssDSSCs.

A compact layer (blocking layer) can effectively block the direct contact between the fluorine-doped tin oxide (FTO) glass substrate and electrolyte in dye-sensitized solar cells (DSSCs). The TiCl 4 hydrolysis has been widely adopted for preparing the TiO 2 compact layer (H-TiO 2 ). However, the TiCl 4 aqueous solution is unstable for its high reactivity. To improve the chemical stability of TiCl 4 aqueous solution, the Ti 4+ is encapsulated by the polymer, polyethyleneimine (PEI). Experimentals show that the Ti-PEI precursor solution can maintain their initial performances for several months. The resulting TiO 2 film (P-TiO 2 ) grown by the Ti-PEI precursor is dense, smooth and uniform without any visible and detectable cracks or voids. The P-TiO 2 compact layer is even denser than the H-TiO 2 compact layer, suggesting reducing the electron recombination and prolonging the electron lifetime in dye-sensitized solar cells. Indeed, the electron lifetime of the DSSC based on the P-TiO 2 is 13.15 ms, which is longer than the 10.83 ms based on H-TiO 2 . Meanwhile, the power conversion efficiency of the DSSC based on P-TiO 2 compact film is about 12.5% higher than that based on H-TiO 2 . Therefore, this encapsulation technology can not only improve the stability of the metal ions solution but also meet a large-scale fabrication demand of the TiO 2 compact layer in future DSSCs.

In this study, we report the growth of molybdenum oxide (MoOx) film by polymer-assisted deposition (PAD), an environmentally friendly strategy in an aqueous system. The MoOx film has good crystal quality and is dense and smooth. The transparency of the film is >95% in the wavelength range of 300–900 nm. The device based on P3HT:PCBM absorber material was fabricated. The solar cell with PAD-MoOx as an anode interfacial layer exhibits great performance, even better than that of a solar cell with PEDOT:PSS or evaporated MoOx as an anode interfacial layer. More importantly, the solar cells based on the growth of MoOx have a longer term stability than that of solar cells based on PEDOT:PSS. These results demonstrate the aqueous PAD technology provides an alternative strategy not only for the thin films’ growth of applied materials but also for the solution processing for the low-cost fabrication of future materials to be applied in the field of solar cells.

Monodisperse CdS quantum dots (QDs) are synthesized by thermal decomposition of organic complexes in the system of the cost-effective commercial 0# diesel at 200 °C. The prepared CdS QDs have a good dispersion and high crystallization. When the CdS QDs are doped into the blends of poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6, 6)C61 (PCBM) for hybrid solar cells (HSCs), the HSCs achieve about 25% increase of power conversion efficiency in comparison to the reference device without the CdS QDs. The improvement of the cell performance mainly attributes to the increased short-circuit current density arising from the absorption enhancement in the wavelength range of 350–550 nm by introducing the synthesized CdS QDs into the P3HT: PCBM active layer.

New fabrication techniques for solution-processed organic photovoltaics are more and more desirable due to greater demand for affordable method to make large area. Different from traditional spin-coating, here, we report a new fabrication technique inspired by “liquid-chalk”. Solution can be added into liquid-chalk, and is almost all coated on the devices, while spin-coating will waste most of solution. In addition, large area could be easily achieved with it. Meanwhile, the thickness and roughness could be adjusted by optimizing speed, time of annealing and amount of the solution added. We demonstrated solar cells based on liquid-chalk-coated perovskite photoactive layer (CH3NH3PbI3) exhibit comparatively high power con-version efficiency (PCE) of 14.83% on average. A champion PCE of 16.04% was attained. Similarly, applying the method in pure inorganic system (CsPbBrI2), we also successfully fabricated devices with a highest PCE of 9.17%. The results indicate that using liquid-chalk to coat is an effective new way to fabricate perovskite solar cells, and also an ideal method to make large-area and flexible devices.

A facile strategy was developed to simultaneously improve the performance and stability of perovskite solar cells (PSCs). It involves the dissolution of an ultranarrow bandgap material, (2,2′-((2Z,2′Z)-(((4,4,9,9-tetrakis (4-hexylphenyl)-4,9-dihydro-s-indaceno [1,2-b:5,6-b′] dithiophene-2,7-diyl) bis (4-((2-ethylhexyl) oxy) thiophene-5,2-diyl))bis(methanylylidene))bis(5,6-difluoro-3-oxo-2,3-dihydro-1H-indene-2,1-diylidene)) dimalononitrile (IEICO-4F)), in chlorobenzene (antisolvent), the use of the solution in the treatment of perovskite films during spin-coating, and the fabrication of solar cells using the treated perovskite films. IEICO-4F formed a charge transfer bridge at the perovskite/Spiro-OMeTAD interface and improved the charge extraction and transport. Furthermore, the addition of IEICO-4F facilitated the crystallization, improved the surface morphology, and enhanced the passivation of trap sites of perovskite films. Meanwhile, a reliable power conversion efficiency exceeding 20% for CH3NH3PbI3-based cells and 15.72% for CsPbBrI2-based all-inorganic PSCs was realized. These values surpass those of the control devices (i.e., 18.66% and 13.30%, respectively).

We report oxygen vacancies (OVs) rich hexagonal ReO3 nanostructured electrocatalysts for efficient hydrogen generation. Through a simple argon plasma exposure, OVs are introduced into the ReO3 nanoparticles (NP) and nanosheets to enhance electrocatalytic activities with decreasing overpotentails from 157 mV and 178 mV to 138 mV and 145 mV at the current density of 10 mA cm-2, respectively. As-processed OVs rich ReO3 NP exhibit a good stability during electrochemical measurements for 20 h in acidic electrolyte. The huge active surface area, abundant OVs and excellent conductivity contribute to the performance according to the experimental data. Further theoretical calculations show that the abundant OVs adsorb H with lower Gibbs free energy facilitating hydrogen evolution.

A direct comparison of charge transport and electronic traps in representative polymer–fullerene blend, poly (3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM), is carried out in dark and illuminated conditions based on the measurements of temperature-dependent current–voltage characteristics. In dark condition, the charge transport presents a transition from Ohmic to trap-limited current. While the trap-filled space charge limited current is observed under illumination at the same applied bias. From evaluations of trap density and energy distribution by a differential method, it is reveal that the diverse charge transport in dark and illuminated conditions is mainly caused by the different trap states distribution, which strongly affects the space charges and the electrical field in P3HT: PCBM blends.

Molybdenum trioxide (MoO 3 ) doped organic semiconductors have shown attractive applications in organic electric devices. The authors carried out an investigation on the origin of enhanced photoelectric characteristics in MoO 3 -doped pentacene films. Electrical properties including charge transport, trap density and conductivity in bulk MoO 3 -doped pentacene films were investigated through fundamental measurements of current-voltage characteristics. Electrical structure and conducting mechanism in MoO 3 -doped pentacene films were further evaluated by X-ray diffraction and X-ray photoelectron spectroscopy measurements. The experimental results suggest that the improved conductivity in MoO 3 -doped pentacene film was partly associated with the increased ratio of low Mo oxidation state (Mo 4+ ) with a fact of better conducting property of MoO 2 than that MoO 3 .

The underlayer plays an important role for organic–inorganic hybrid perovskite formation and charge transport in perovskite solar cells (PSCs). Here, we employ a classical organic small molecule, 5,6,11,12-tetraphenyltetracene (rubrene), as the underlayer of perovskite films to achieve 15.83% of power conversion efficiency with remarkable moisture tolerance exposed to the atmosphere. Experiments demonstrate rubrene hydrophobic underlayer not only drives the crystalline grain growth of high quality perovskite, but also contributes to the moisture tolerance of PSCs. Moreover, the matching energy level of the desirable underlayer is conductive to extracting holes and blocking electrons at anode in PSCs. This introduction of organic small molecule into PSCs provides alternative materials for interface optimization, as well as platform for flexible and wearable solar cells.

Roll-off phenomena in power efficiency for rubrene-based mixed single layer organic light emitting devices is investigated. The evaluation of operational temperature demonstrates that Joule heating is not the main reason for roll-off in power efficiency with current density. Co-doping method through rubrene co-doping with some additive dopant, C6, DCJTB and Nile red, in mixed single layer are proposed for suppressing the roll-off in power efficiency. By co-doping suitable Nile red with rubrene, the efficiency roll-off is found to be largely improved in whole range of current density. Moreover, improved device performance is also realized even if with a 3 wt% fluorescent doping concentration. The improved performance is ascribed that there exists a competitive emission mechanism with respect to different dopant.

Electroluminescence and photovoltaic properties were observed simultaneously in a small molecular rubrene-doped poly(3-hexylthiophene):1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 blends based organic solar cells (OSCs). With optimized rubrene doping ratio, the device showed photovoltaic (PV) property with a power convention efficiency 1.05% under illumination and electroluminescence (EL) characteristics with a maximum luminance 65 cd/m 2 at higher bias, respectively. It provides a new route to realize the PV and EL bi-functional organic devices. In addition, the EL imaging in OSCs is expected to provide valuable information in the film defect conditions for understanding the blends internal conditions, meliorating the film quality, and further improving the device performance.

The authors investigate the effects of metal work functions on charge transport characteristics in P3HT:PCBM bulk heterojunction under illumination by evaluating the temperature dependence of current–voltage characteristics. Schottky thermal emission current plays a dominant role on charge transport in the devices with Au or Al alloys used as electrodes. Whereas, a combined bulk limited conduction mechanism corresponding to three-dimensional variable-range hopping model and space charge limited current (SCLC) with an exponential distribution of traps (filled and unfilled) occurs in the device with Al used as electrode. And a shift to LUMO state of PCBM for trap density distribution is observed due to temperature dependence of Fermi level in PCBM material.

It will be interesting and valuable information can be achieved if a direct comparison between organic light emitting devices (OLEDs) fabricated by vacuum evaporated method (vac) and solution-based manufacturing processes (sol) was realized. Small molecular OLEDs with a mixed organic layer structure (MOLOLEDs) make it possible for direct comparison between devices with the same materials but fabricated by the two processing methods. This article shows a direct comparison of the luminescence characteristics, charge conduction, and device physics between MOLOLEDs fabricated by vac- and sol-processing techniques. It gives an elementary explain how the organic/metal interfaces influence the charge conduction and device performance.

Injection properties of electrons and holes at the interface of electrodes/active layer for blending poly(3-hexylthiophene) (P3HT) and methanofullerene [6,6]-phenyl–C61–butyric acid methyl ester (PCBM) based on structures of Au/MoO3/P3HT: PCBM/ MoO3/Au as hole dominated device and Al alloy/P3HT: PCBM/Al alloy as electron dominated device were investigated. Both of hole and electron injections were ascribed to Schottky thermionic emission mechanism. The barrier height of carrier injection was estimated under a simulated air mass (AM) 1.5G spectrum illumination and dark conditions, respectively. The interfacial state at Al alloys/ P3HT: PCBM interface was estimated to be 1.4 × 1014 states/cm2/eV under illumination by extrapolating the relation of electron barrier heights and work functions using different Al alloys.

Inverted top-emission organic light emitting devices (TEOLEDs) with a mixed single layer by mixing of electron transport materials (PyPySPyPy and Alq 3 ), hole transport material (α-NPD) and dope material (rubrene) were investigated. Maximum power efficiency of 3.5 lm/W and maximum luminance of 7000 cd/m 2 were obtained by optimizing the mixing ratio of PyPySPyPy:Alq 3 :α-NPD:rubrene=25:50:25:1. Luminance and power efficiency of mixed single layer device were two times improved compared to bi-layer heterojunction device and tri-layer heterojunction device. Lifetime test also shows that the mixed single layer device exhibits longer operational lifetimes of 343 h, which is three times longer than the 109 h for tri-layer device, and two times longer than the 158 h for bi-layer device. In addition, the maximum luminance and power efficiency were obtained at 20,000 cd/m 2 and 7.5 lm/W, respectively, when a TPD layer of 45 nm was capped onto the top metal electrode.

The relative densities of SiCln (n = 0–2) in SiCl4 radio frequency (rf) glow discharge plasma are measured by mass spectrometry. The effects of discharge parameters, i.e., rf power, discharge pressure, substrate temperature, and SiCl4 flow rate on the relative densities of SiCln (n = 0–2) are investigated in detail. An optimum configuration of discharge parameters (low rf power, high discharge pressure, low substrate temperature, and low flow rate), which enhanced the formation of SiCln (n = 0–2) radicals, is searched by a great deal of measurements and discussions. In the optimum configuration of discharge parameters, we measure the spatial distribution of SiCln (n = 0–2) radicals in the most optimized plasma parameters. The experimental results reveal that Si and SiCl may be the dominant precursors in forming the thin film.

The authors developed a seed-mediated method by GeO2 nano-particles (NPs) for growing crystal perovskite films. Poly(3,4-ethylene dioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS)-GeO2 composite films can act as an efficient underlayer for the growth of crystal perovskite films. GeO2 NPs are regarded as the growing sites of crystal nucleus of the perovskites. Superior quality of perovskite films are achieved by tuning the size of the GeO2 NPs, which results in a power conversion efficiency as high as 16.77%. The seed-mediated growing route on perovskite crystallization also gives a hint to seek other nano-particle materials for fabricating highly efficient and stable perovskite solar cells in the future.

The authors investigate the influence of two hole interfacial materials poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) and aqueous solution-processed MoO3 (sMoO3) on cell stability. sMoO3-based device demonstrated obviously improved stability compared to PEDOT:PSS-based one. Current-voltage characteristics analysis is carried out to investigate the effect of the hole interfacial layers on the cell stability. The formation of additional trap states at the interfaces between the hole interfacial layer and the active layer in degraded devices is verified by a differential method. Improved cell stability is attributed to a relatively stable sMoO3 interfacial layer compared to PEDOT:PSS by comparing their different trap states distributions.

Transparent p-type nickel oxide (NiO) thin films have been epitaxially grown on (0001) Al2O3 substrates by a chemical solution method of polymer-assisted deposition for the first time. The films have a high optical transparency of above 95% in the wavelength range of 350-900 nm.

The authors demonstrate a pentacene/C60 heterojunction organic solar cell utilizing MoO3-doped pentacene thin films as an interfacial layer at anode and a multicharge-separation layer between pentacene and C60, respectively. The short-circuit current density and the open-circuit voltage were improved simultaneously compared with the reference device, resulting in an improvement in power conversion efficiency from 0.97% to 2.29%. Absorption spectra measurement, surface morphology analysis, and interfacial evaluation at anode side in the hole-dominant devices were carried out to reveal the functions of MoO3-doped pentacene films in OSCs.

We report the synthesis of carbon nanotube/TiC hybrid fibers using a polymer-assisted chemical solution approach. Ti metal ions are bound to aqueous polyethyleneimine (PEI) to form precursor solution. Amphiphilic PEI with Ti easily permeates the CNT fibers. Upon annealing in a controlled atmosphere, a homogeneous TiC network is formed in the CNT fibers. The obtained CNT/TiC hybrid fibers show prominent enhancement in mechanical strength and electrical conductivity. The tensile strength and conductivity of CNT/TiC fibers can be improved to 0.67 GPa and 1650 S cm(-1) at room temperature, respectively. More importantly, a tensile modulus as high as 420 GPa has been achieved for the CNT/TiC fibers. Analysis shows that the cross-linking matrix of hard TiC plays a significant role in the improvement of mechanical strength. Furthermore, the electrons are transported in the CNT/TiC fiber by a three dimensional hopping mechanism.

The authors investigate the effects of compressive stress on the performance of organic solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blends. The short-circuit current density is improved, and a maximum 16% enhancement in power conversion efficiency is achieved by introducing suitable a stress into the device. The improved performance is attributed to the formation of a good contact between the Al cathode and the P3HT:PCBM blend owing to the introduction of a suitable compressive stress. Meanwhile, the barrier height at Al/blend is lowered from 0.34 to 0.23 eV by evaluating the temperature dependence of the current–voltage characteristics.

Measurements of the current density–voltage (J–V) characteristics of a poly(3-hexylthiophene) (P3HT) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 (PCBM)-based electron-dominated device as functions of temperature were carried out. A transport transition from three-dimensional variable range hopping (VRH) to space-charge-limited current (SCLC) with an exponential distribution of traps (filled and unfilled) was observed. The bulk trap density, about 1018 cm-3, of the P3HT:PCBM blend film was evaluated by the differential method. A shift to the lowest unoccupied molecular orbital (LUMO) state of PCBM for trap density distribution was observed owing to the temperature dependence of the Fermi level of PCBM materials. It is supposed that the Fermi level of PCBM materials is strongly temperature-dependent similarly to that of amorphous silicon semiconductors.

We report on the enhanced carrier injection in pentacene thin-film transistors with a thin MoO3-doped pentacene layer between pentacene semiconductor and the source-drain electrodes. Device performance including drain current, field effect mobility, and threshed voltage are improved by employing a MoO3-doped pentacene thin layer. The barrier height at the Au/pentacene interface is lowered from 0.12 to 0.05 eV after inserting a MoO3-doped pentacene thin layer between them. The reduced barrier height is attributed to the formation of a good contact between MoO3-doped pentacene and Au owing to smoothed surface morphology of pentancene and suitable band bending by MoO3 doping.

A highly simplified single layer solution-processed phosphorescent organic light emitting device (PHOLED) with the maximum ηP 11.5 lm/W corresponding to EQE 9.6% has been demonstrated. The solution-processed device is shown having comparable even exceeding device performance to vacuum-processed PHOLED. The simplified device design strategy represents a pathway toward large area, low cost and high efficiency OLEDs in the future. The charge injection and conduction mechanisms in two solution- and vacuum-processed devices are also investigated by evaluating the temperature dependence of current density – voltage characteristics.