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(Received 2 March 2016; accepted 15 June 2016; published online 24 June 2016) The performance of organic optoelectronic devices can be improved by employing a suitable optical cavity design beyond the standard plane layer approach, e.g., by the inclusion of periodically or randomly textured structures which increase light incoupling or extraction. One of the simplest approaches is to add an additional layer containing light scattering particles into the device stack. Solution processed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films are promising for replacing the brittle and expensive indium tin oxide transparent electrode. We use a blend of 100 nm TiO2 scattering particles in PEDOT:PSS solution to fabricate transparent electrode films which also functions as a scattering layer. When utilized in an organic photovoltaic device, a power conversion efficiency of 7.92% is achieved, which is an 8.6% relative improvement compared to a device with a neat PEDOT:PSS electrode without the nanoparticles. This improvement is caused by an increase in short-circuit current due to an improved photon harvesting in the 320 nm-700 nm spectral wavelength range. [ABSTRACT FROM AUTHOR]

The article offers information on the use of hybrid electrodes with a combination of ultratransparent poly(3,4-ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT:PSS) and an evaporated semitransparent silver (Ag) grid for small-molecule organic solar cells. Topics discussed include electrical and optical properties as well as excellent mechanical flexibility of indium-tin oxide (ITO), performance of Organic photovoltaic (OPV) cells and characteristics of various electrodes.

The article offers information on a study which examines ultratransparent poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)(PEDOT:PSS) and silver (Ag) grid hybrid electrodes for organic photovoltaic (OPV) cells. An oxygen plasma etching process was performed to prepare the PEDOT:PSS thin films. It shows the potential of hybrid electrodes for effective OPV cells.

Highly transparent electrodes are demonstrated based on thermally evaporated calcium:silver blend thin-films, which show unusually high transmission well above the expectations from bulk material properties and thin film optics. These electrodes exhibit a low sheet resistance of 27.3 Ω/, combined with an extraordinarily high mean transmittance of 93.0% in the visible spectral range (σdc/σopt = 186.7), superior to the commonly used inorganic electrodes made from indium tin oxide (ITO). Additionally, the metal blend electrode is flexible, showing a constant sheet resistance down to a bending radius of 10 mm and can be employed on top of organic devices without causing damage to the organic material. The spontaneously formed unique microstructure of a polycrystalline Ag network with randomly distributed nanoapertures, surrounded by a calcium shell, enables broadband transmittance enhancement due to amplified plasmonic coupling. Consequently, top-illuminated organic solar cells using such metal blend electrodes achieve a power conversion efficiency of 7.2% (which defines a new record for top illuminated organic solar cells) and even exceed the efficiency of similar bottom-illuminated reference solar cells (6.9%) employing common ITO electrodes. [ABSTRACT FROM AUTHOR]

Abstract: Percolation networks from silver nanowires can be used as a transparent electrode and promising alternative to the commonly used ITO. Here, the deposition of such a nanowire based network by dip coating, a versatile and scalable method, is described and characterized in detail. After identifying appropriate processing parameters, nanowire grids with conductivity and transmittance values rivaling ITO have been achieved. As a main issue, the roughness of the film was addressed and the influence on the device in terms of shunt paths was investigated. Using this network as anode, small molecule organic solar cells with varying stack structure were fabricated and yield efficiencies comparable to cells on ITO. [Copyright &y& Elsevier]

Transparent conductive oxides and alternative transparent electrodes for organic photovoltaics and OLEDs Organic, photoactive devices, such as OLEDs or organic solar cells, currently use indium tin oxide (ITO) as transparent electrode. Whereas ITO is industry-proven for many years and shows very good electrical and optical properties, its application for lowcost and flexible devices might not be optimal. For such applications innovative technologies such as networkbased metal nanowire or carbon nanotube electrodes, graphene, conductive polymers, metal thin-films and alternative transparent conductive oxides emerge. Although some of these technologies are rather experimental and far from application, some of them have the potential to replace ITO in selected applications. [ABSTRACT FROM AUTHOR]

Abstract: We have developed semi-transparent n–i–p organic solar cells (OSC) with free-standing multi-wall carbon nanotube (f-CNT) sheets as transparent top electrodes. By a simple and damage-free room temperature orthogonal liquid solution assisted self-laminating process, f-CNT top electrodes are successfully deposited on top of ZnPc:C60 bulk heterojunction small molecule OSCs. The cells show high fill factors above 58% as well as efficiencies up to 1.5% and greater long-term stability compared to the device having a metal electrode. For the given cell structure with f-CNT semi-transparent electrodes, the influence of an optical spacer on light absorption is studied by a systematic variation of the hole transport layer thickness, supported by optical simulations. The results strongly indicate that OSCs with f-CNT top electrodes and optimized thin film stack are highly promising for semi-transparent OSCs, which can be used in tandem devices, in tinted smart windows, and similar applications by a simple and damage-free process in roll-to-roll configuration that can be scaled to large area manufacturing. [Copyright &y& Elsevier]

Abstract: Systematic studies of domain boundaries of self-assembled monolayers of octanethiols on (111) oriented gold surfaces have been performed by ultrahigh vacuum scanning tunnelling microscopy (STM). The monolayers consist of domains that exhibit the superstructure of the hexagonal structure of alkanethiols on gold. By high-resolution images domain boundaries are displayed with molecular resolution. These are used to deduce the exact relation between the adsorption sites of the molecules belonging to different domains on the gold substrate. A translational transition is shown here in detail and it is demonstrated that hexagonal close-packed (hcp), and face-centred cubic (fcc) triple hollow sites are occupied similarly by octanethiols. [Copyright &y& Elsevier]

Abstract: The self-assembly of ω-ferrocenylalkanethiols (FcCnSH) with different alkyl-spacer lengths on Au(111) substrates has been studied by scanning tunneling microscopy (STM). Upon deposition at room temperature FcCnSH molecules tend to form multilayers, while by thermal treatment monolayer formation, a rearrangement of the molecules and the formation of ordered domains is achieved. The surface structure of the resulting full coverage self-assembled monolayers is resolved with molecular resolution by STM. The ordered monolayer structure of ω-ferrocenylpropanethiol is discussed in comparison with its bulk crystal structure, derived from single crystal X-ray analysis. Based on these results a monolayer structure of ω-ferrocenylalkanethiols with longer alkyl chains closely related to the bulk crystal structure of the shorter alkyl-spacer derivates is suggested. Our results provide detailed insight into the self-assembly of FcCnSH on gold substrates. [Copyright &y& Elsevier]

A hybrid electrode with a combination of an ultratransparent conductive polymer (nearly 100% transparency) and a semitransparent silver grid is developed for organic photovoltaic cells. In article number 1401822, Yong Hyun Kim and co‐workers report that the hybrid electrode shows an improvement of the photovoltaic performance and a potential to reduce a significant resistive power loss in large‐area devices. These hybrid electrodes will contribute the development of low‐cost, efficient, large‐area organic photovoltaic cells. [ABSTRACT FROM AUTHOR]

Flexible aluminum moisture barrier films are shown to meet ultra-barrier requirements with water vapor transmission rates as low as 1*10 −4 g/m 2 /day at 38 °C and 90% R.H. These low transmission rates are achieved by lamination of two films that are independently processed on individual substrates. The integration in organic electronic devices like organic solar cells or OLEDs is particularly easy in a single lamination step, since an existing aluminum electrode can be utilized as one half of the moisture barrier. The resulting laminate maintains flexibility of the device and improves the barrier quality by an order of magnitude compared to conventional stacking of two barriers. Organic solar cells with this type of encapsulation are manufactured and aged in controlled climate. They do not exhibit significant extrinsic degradation. [ABSTRACT FROM AUTHOR]

Planarization and filling voids between wires are key issues when using nanowire electrodes in flexible solar cells such as organic photovoltaics (OPV). For this purpose, we use poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) which leads to an electrically well connected silver nanowire (AgNW) network. Furthermore, the use of water based PEDOT: PSS leads to humidity assisted AgNW fusing, resulting in a maximum processing temperature of only 120 °C. OPV cells using this AgNW/PEDOT: PSS transparent electrodes exhibit power conversion efficiencies up to 7.15%. Moreover, OPV devices on PET substrates with an alumina encapsulation and barrier adhesive show excellent mechanical flexibility. [ABSTRACT FROM AUTHOR]

Highly efficient nanolaminate diffusion barriers made of TiO 2 /Al 2 O 3 multilayers using low temperature atomic layer deposition optimized for organic light emitting diodes are presented. Water vapour transmission rates (WVTR) show values of the order of 10 −3 g/m 2 /d at 38 °C, 90% RH on planarized PEN webs (pPEN) when ozone is used as the oxidizing precursor for Al 2 O 3 deposition. OLED encapsulated with such diffusion barriers display few dark spots observed over 2000 h after deposition and for aging under ambient conditions. Diffusion barriers deposited using water as the oxidizing precursor for Al 2 O 3 result in at least 10 times lower WVTR on pPEN webs (10 −4 g/m 2 /d). However, these water based diffusion barriers are incompatible with OLEDs such that the latter show extensive black spot formation (areas of no visible luminescence) immediately after deposition. Finally through the growth of these initial black spots, more than 40% loss in initial luminescence occurs after merely 900 h of operation. In this report, we introduce a new methodology for OLED encapsulation using a two step process where 10 nm thick ozone Al 2 O 3 based nanolaminate diffusion barrier is followed by a 90 nm thick water Al 2 O 3 based diffusion barrier (keeping TiO 2 precursors always the same). With this novel diffusion barrier stack, no visible black spot growth is observed over 2000 continuous operation hours under ambient conditions. Simultaneously, high OLED luminescence representing 90% of the initial luminescence value, which is measured at t = 0 is maintained after 2000 h of operation. Low WVTR values in the 10 −4 g/m 2 /d range on pPEN webs are consistently measured in these essentially water based barrier layers with only 10 nm thick starting ozone Al 2 O 3 based nanolaminate diffusion barriers. The results reported here have implications on developing methodologies for ultra high performance, OLED compatible diffusion barriers by ALD. [ABSTRACT FROM AUTHOR]

Abstract: The growth behavior of thin silver films on organic layers is investigated during deposition by means of simultaneous in-situ monitoring of sheet resistance and transmittance. Thermally evaporated films up to 11nm show a distinct percolation behavior with strong resistance drop at the percolation thickness. Additionally, evaporations are divided into a sequence of one nanometer steps. In the deposition breaks, the films exhibit a ripening effect with an inversion at the percolation thickness, by changing from an increasing to decreasing sheet resistance over time. Scanning electron micrographs suggest same ripening mechanisms for islands below the percolation thickness as for holes above. [Copyright &y& Elsevier]

We present highly transparent and conductive silver thin films in a thermally evaporated dielectric/metal/dielectric (DMD) multilayer architecture as top electrode for efficient small molecule organic solar cells. DMD electrodes are frequently used for optoelectronic devices and exhibit excellent optical and electrical properties. Here, we show that ultrathin seed layers such as calcium, aluminum, and gold of only 1 nm thickness strongly influence the morphology of the subsequently deposited silver layer used as electrode. The wetting of silver on the substrate is significantly improved with increasing surface energy of the seed material resulting in enhanced optical and electrical properties. Typically thermally evaporated silver on a dielectric material forms rough and granular layers which are not closed and not conductive below thicknesses of 10 nm. With gold acting as seed layer, the silver electrode forms a continuous, smooth, conductive layer down to a silver thickness of 3 nm. At 7 nm silver thickness such an electrode exhibits a sheet resistance of 19 Ω/□ and a peak transmittance of 83% at 580 nm wavelength, both superior compared to silver electrodes without seed layer and even to indium tin oxide (ITO). Top-illuminated solar cells using gold/silver double layer electrodes achieve power conversion efficiencies of 4.7%, which is equal to 4.6% observed in bottom-illuminated reference devices employing conventional ITO. The top electrodes investigated here exhibit promising properties for semitransparent solar cells or devices fabricated on opaque substrates. [ABSTRACT FROM AUTHOR]

The performance of both organic light-emitting diodes (OLEDs) and organic solar cells (OSC) depends on efficient coupling between optical far field modes and the emitting/absorbing region of the device. Current approaches towards OLEDs with efficient light-extraction often are limited to single-color emission or require expensive, non-standard substrates or top-down structuring, which reduces compatibility with large-area light sources. Here, we report on integrating solution-processed nano-particle based light-scattering films close to the active region of organic semiconductor devices. In OLEDs, these films efficiently extract light that would otherwise remain trapped in the device. Without additional external outcoupling structures, translucent white OLEDs containing these scattering films achieve luminous efficacies of 46 lm W-1 and external quantum efficiencies of 33% (both at 1000 cd m-2). These are by far the highest numbers ever reported for translucent white OLEDs and the best values in the open literature for any white device on a conventional substrate. By applying additional light-extraction structures, 62 lm W-1 and 46% EQE are reached. Besides universally enhancing light-extraction in various OLED configurations, including flexible, translucent, single-color, and white OLEDs, the nano-particle scattering film boosts the short-circuit current density in translucent organic solar cells by up to 70%. [ABSTRACT FROM AUTHOR]

Recently, organic solar cells have demonstrated high power conversion efficiencies, but extrinsic device stability remains to be a challenge. Often, delamination of the cathode upon water ingress leads to a massive active area loss and to a strong decrease in efficiency. We present highly efficient organic solar cells with an oligothiophene-based donor and two different cathodes. Devices are aged at four different climates under continuous illumination. Al and MoO 3 /Cr/Al cathodes are compared. Additional interlayers are introduced for enhanced cathode adhesion. Aging in different climates reveals a strong dependency of the degradation speed on absolute humidity for standard Al cathodes. However, using additional interlayers, degradation seems to be almost decoupled from the applied climate and device degradation is slowed immensely. Parallel WVTR measurements of the AlO x barrier allow for the assessment of absolute water quantities until devices are degraded to half of their initial efficiency: 24 g m 2 are found for standard Al cathodes, while devices with additional interlayers reach 58 g m 2 . This difference is related to a completely different aging behavior, which trades strong short-circuit current density losses for moderate fill-factor losses. [ABSTRACT FROM AUTHOR]

Atomic layer deposited nanolaminates of alternating AlO x and TiO x thin-films are investigated as moisture barriers for organic electronic devices. Direct encapsulation on organic light emitting diodes (OLEDs) is tested in aging experiments and compared to calcium corrosion tests of equivalent barrier films. This allows for a direct assessment of moisture barrier performance in simple as well as more complex systems. Thickness variations are performed for the nanolaminate single and total layer thickness, with an optimum single layer thickness of 1–2 nm observed. This correlates to the maximum number of dyads once completely closed single layers are produced. For large single layer thickness and low dyad count, strong lateral diffusion from the edges occurs in the OLEDs, which likely correlates to poor mechanical stability. At optimum single layer thickness, barriers remain mechanically and chemically stable up to 100 nm total thickness. OLEDs encapsulated with such nanolaminate barriers show no significant degradation after 2500 h of continuous aging. [ABSTRACT FROM AUTHOR]

Micro-structured organic photovoltaic (OPV) devices on polyethylene terephthalate substrates are produced using direct laser interference patterning (DLIP). The performance of organic solar cells on these substrates is improved by a factor of 1.16, and a power conversion efficiency of 7.70% is achieved. We show that a shorter spatial period of the pattern allows for a stronger light trapping effect in solar cell, as it leads to a longer light path. Moreover, since the patterned structures are located on the outside of the fully encapsulated OPV devices, there are no problems with the roughness induced shunts. [ABSTRACT FROM AUTHOR]

The degradation of sexithiophene cascade organic solar cells is studied. Glass–glass encapsulated devices on indium tin oxide as transparent electrode show efficiencies of 6.6% and degrade within 500 h in illuminated 38 °C/50% RH climate. Fully flexible devices with silver nanowire electrode and alumina barrier achieve 5% efficiency and degrade within 30 h due to electrode failure. [ABSTRACT FROM AUTHOR]

We measure basic network parameters of silver nanowire (AgNW) networks commonly used as transparent conducting electrodes in organic optoelectronic devices. By means of four point probing with nanoprobes, the wire-to-wire junction resistance and the resistance of single nanowires are measured. The resistance RNW of a single nanowire shows a value of RNW = (4.9±60.18)Ω/µm. The junction resistance RJ differs for annealed and non-annealed NW networks, exhibiting values of RJ = (25.2±1.9)Ω (annealed) and RJ = (529±239)Ω (non-annealed), respectively. Our simulation achieves a good agreement between the measured network parameters and the sheet resistance RS of the entire network. Extrapolating RJ to zero, our study show that we are close to the electrical limit of the conductivity of our AgNW system: We obtain a possible RS reduction by only ≈20% (common RS 10Ω/sq). Therefore, we expect further performance improvements in AgNW systems mainly by increasing NW length or by utilizing novel network geometries. [ABSTRACT FROM AUTHOR]

We report about solution-processing of a doped small molecule hole transport layer (s-HTL) comprising of N,N′-((diphenyl-N,N′-bis)9,9,-dimethyl-fluoren-2-yl)-benzidine (BF-DPB) as matrix and the p-dopant “NDP9” in the non-halogenated solvent tetrahydrofuran (THF). We show that the doping process is already happening in solution and stays effective after coating. Conductivities achieved with this process are comparable to those reached by thermal co-evaporation under high vacuum, which is the usual deposition method for this material. Applied as planarization layer onto AgNW films with best performance values of 15 Ω / □ and 83.5% total transmission including the substrate, the s-HTL is proving its ability to sufficiently smoothen the initially rough AgNW topography. We analyze the necessary lateral conductivity to bridge micrometer-large voids in the mesh, as they are inherent in nanowire network electrodes. In combination with zinc phtalocyanine:C 60 organic solar cells, a s-HTL conductivity less than 1 × 10 −4 S/cm can lead to decreased device performance with a loss greater than 10% for nanowires with 90 nm diameter and the associated mesh width. Furthermore, we demonstrate more efficient vacuum-deposited p-i-n solar cells with an oligothiophene (DCV5T-Me) as donor, C 60 as acceptor. They exhibit power conversion efficiencies up to 4.4% on AgNW bottom electrodes with s-HTL, compared to 4.1% on ITO with s-HTL as reference device. [ABSTRACT FROM AUTHOR]

Pulsed laser deposited gallium doped zinc oxide (ZnO:Ga) is reported as transparent top electrode for organic solar cells. In contrast to standard coating techniques, prone to harm organic sublayers and leading to strongly reduced device efficiencies, eclipse pulsed laser deposition (PLD) in argon atmosphere is identified as compatible, nonharmful deposition method for ZnO:Ga, even on top of sensitive organic material. Although PLD is not yet ready for mass production, the experiments reveal and solve crucial process limitations, e.g., droplet impacts, which might be useful also for high yield deposition methods. Optimized ZnO:Ga top electrodes achieve a high mean transparency in the visible spectral range of Tvis = 82.7% and a reasonable sheet resistance of RS = 83 Ω sq−1. The organic photovoltaic devices prepared with this electrode obtained an efficiency of η = 2.9%, almost equal to the efficiency of reference samples using a state-of-the-art metal top contact ( η = 3.0%). The investigations here demonstrate the successful deposition of transparent conductive oxides as top electrode for organic devices and open a new path towards the combination of metal oxides and organic semiconductors. [ABSTRACT FROM AUTHOR]

Organic devices like organic light emitting diodes (OLEDs) or organic solar cells degrade fast when exposed to ambient air. Hence, thin-films acting as permeation barriers are needed for their protection. Atomic layer deposition (ALD) is known to be one of the best technologies to reach barriers with a low defect density at gentle process conditions. As well, ALD is reported to be one of the thinnest barrier layers, with a critical thickness – defining a continuous barrier film – as low as 5–10 nm for ALD processed Al 2 O 3 . In this work, we investigate the barrier performance of Al 2 O 3 films processed by ALD at 80 °C with trimethylaluminum and ozone as precursors. The coverage of defects in such films is investigated on a 5 nm thick Al 2 O 3 film, i.e. below the critical thickness, on calcium using atomic force microscopy (AFM). We find for this sub-critical thickness regime that all spots giving raise to water ingress on the 20 × 20 μm 2 scan range are positioned on nearly flat surface sites without the presence of particles or large substrate features. Hence below the critical thickness, ALD leaves open or at least weakly covered spots even on feature-free surface sites. The thickness dependent performance of these barrier films is investigated for thicknesses ranging from 15 to 100 nm, i.e. above the assumed critical film thickness of this system. To measure the barrier performance, electrical calcium corrosion tests are used in order to measure the water vapor transmission rate (WVTR), electrodeposition is used in order to decorate and count defects, and dark spot growth on OLEDs is used in order to confirm the results for real devices. For 15–25 nm barrier thickness, we observe an exponential decrease in defect density with barrier thickness which explains the likewise observed exponential decrease in WVTR and OLED degradation rate. Above 25 nm, a further increase in barrier thickness leads to a further exponential decrease in defect density, but an only sub-exponential decrease in WVTR and OLED degradation rate. In conclusion, the performance of the thin Al 2 O 3 permeation barrier is dominated by its defect density. This defect density is reduced exponentially with increasing barrier thickness for alumina thicknesses of up to at least 25 nm. [ABSTRACT FROM AUTHOR]

Highlights: [•] Color-stable, ITO-free white OLEDs with enhanced efficiencies were demonstrated. [•] High-conductivity PEDOT:PSS was used as the transparent anode. [•] Nanoparticle-based scattering layers were used for light extraction. [•] Both can be fabricated by simple, low-temperature solution processing. [•] Such an approach simultaneously provides manufacturing, cost and efficiency advantages. [ABSTRACT FROM AUTHOR]

Conventional planar organic light-emitting diodes (OLEDs) suffer from poor light extraction due to the total internal reflection at the waveguided interfaces. Therefore, the development of efficient light extraction structures is of great necessity and significance to realize practical applications in large area and cost-effective light sources. In this paper, a high-performance internal light outcoupling system for white OLEDs with spontaneously formed metal oxide nanostructures is developed. The fabrication process of the outcoupling system is simple and can be scaled to large area manufacturing. The enhancement of external quantum efficiency in white OLEDs comprising the outcoupling system reaches a factor of 1.7, and it is further increased to 2.9 when a hemispherical lens is employed. Together with the improvement of light extraction, excellent color stability over broad viewing angles is achieved. [ABSTRACT FROM AUTHOR]

The great potential of solution-processed metal nanowire networks utilized as a transparent electrode has attracted much attention in the last years. Typically, silver nanowires are applied, although their replacement by more abundant and cheaper materials is of interest. Here, a hydrazine-free synthesis route for high aspect ratio copper nanowires is used to prepare conductive networks showing an enhanced electrode performance. The network deposition is done with a scalable spray-coating process on glass and on polymer foils. By a pressing or an annealing step, highly conductive transparent electrodes are obtained, and they reveal transmittance-resistance values similar to indium tin oxide (ITO) and networks made of silver nanowires. The application potential of the copper nanowire electrodes is demonstrated by integrating them into an evaporated small-molecule organic solar cell with 3% efficiency. [ABSTRACT FROM AUTHOR]

Efficient transparent organic light-emitting diodes (OLEDs) with improved stability based on conductive, transparent poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) electrodes are reported. Based on optical simulations, the device structures are carefully optimized by tuning the thickness of doped transport layers and electrodes. As a result, the performance of PEDOT:PSS-based OLEDs reaches that of indium tin oxide (ITO)-based reference devices. The efficiency and the long-term stability of PEDOT:PSS-based OLEDs are significantly improved. The structure engineering demonstrated in this study greatly enhances the overall performances of ITO-free transparent OLEDs in terms of efficiency, lifetime, and transmittance. These results indicate that PEDOT:PSS-based OLEDs have a promising future for practical applications in low-cost and flexible device manufacturing. [ABSTRACT FROM AUTHOR]

High performance indium tin oxide (ITO)-free small molecule organic solar cells and organic light-emitting diodes (OLEDs) are demonstrated using optimized ZnO electrodes with alternative non-metallic co-dopants. The co-doping of hydrogen and fluorine reduces the metal content of ZnO thin films, resulting in a low absorption coefficient, a high transmittance, and a low refractive index as well as the high conductivity, which are needed for the application in organic solar cells and OLEDs. While the established metal-doped ZnO films have good electrical and optical properties, their application in organic devices is not as efficient as other alternative electrode approaches. The optimized ZnO electrodes presented here are employed in organic solar cells as well as OLEDs and allow not only the replacement of ITO, but also significantly improve the efficiency compared to lab-standard ITO. The enhanced performance is attributed to outstanding optical properties and spontaneously nanostructured surfaces of the ZnO films with non-metallic co-dopants and their straightforward integration with molecular doping technology, which avoids several common drawbacks of ZnO electrodes. The observations show that optimized ZnO films with non-metallic co-dopants are a promising and competitive electrode for low-cost and high performance organic solar cells and OLEDs. [ABSTRACT FROM AUTHOR]

The importance of O3 pulse duration for encapsulation of organic light emitting diodes (OLEDs) with ultra thin inorganic atomic layer deposited Al2O3 layers is demonstrated for deposition temperatures of 50 °C. X-ray reflectivity (XRR) measurements show that O3 pulse durations longer than 15 s produce dense and thin Al2O3 layers. Correspondingly, black spot growth is not observed in OLEDs encapsulated with such layers during 91 days of aging under ambient conditions. This implies that XRR can be used as a tool for process optimization of OLED encapsulation layers leading to devices with long lifetimes. [ABSTRACT FROM AUTHOR]

n‐Doped C60 is reported as a new electrode material for indium‐tin‐oxide‐free organic solar cells. All layers from the bottom to top electrode are prepared in one step in a vacuum chamber. The organic solar cells based on the n‐C60 electrodes assisted by a semitransparent metal grid exhibit efficiencies as high as 2.9%. [ABSTRACT FROM AUTHOR]

Abstract: We report on transparent stand alone C60 top electrodes for small molecule based organic photovoltaic cells. All device layers (including bottom and top electrode) are thermally evaporated in vacuum, guaranteeing fast, reliable, high-purity and low-cost processing. Employing an organic compound as electrode avoids refractive index mismatch between contact and photo-active layer which results in an increased number of photons reaching the absorber layers. The conductivity of C60 is improved from 10−8 S/cm to remarkable 4.97S/cm by optimized molecular n-type doping. Furthermore, it is shown that high doping concentrations change the absorption behavior of C60, leading to transmittance values over 70% for wavelengths larger than 600nm with a weak dependence on layer thickness. Organic solar cells employing such an optimized n-doped C60 top electrode (thickness 200nm, doping concentration 16wt%) exhibit power conversion efficiencies of 1.53%. Electrical device simulations based on a discretized equivalent circuit model reveal an efficient lateral charge transport in n-doped C60 electrodes over a few 100µm. In combination with a supporting grid electrode (usually employed for large area photovoltaic applications), n-doped C60 might replace ITO and fill the lack of transparent conductive top electrodes required for roll-to-roll processed semi-transparent organic devices or devices on opaque substrates. [Copyright &y& Elsevier]

Abstract: The performance of organic solar cells strongly depends on the nanoscale structure of the used mixed absorber layer. Utilizing photoconductive and conductive atomic force microscopy (pcAFM and cAFM), as well as transmission X-ray microscopy (TXM), we investigate the influence of different substrate temperatures T sub on the thin-film structure and local photocurrent in bulk-heterojunctions (BHJs) of vacuum deposited zinc phthalocyanine (ZnPc) and Buckminsterfullerene (C60) mixed absorber layers. In this paper, we present topography maps, photocurrent maps under short-circuit current conditions, dark-current maps, and TXM images with high lateral resolution down to 25nm. We observe a strong influence of the substrate temperatures during deposition T sub on the nanoscopical segregation of the two components in the BHJ. This segregation leads to a spatial extension of the dark-current and a reduced short-circuit current at higher substrate deposition temperatures T sub. [Copyright &y& Elsevier]

The cover illustrates a flexible small molecule solar cell with three different semitransparent silverbased top electrodes using varying seed layers. With increasing surface energy of the seed layer, the wetting of subsequently deposited silver is significantly improved as indicated in the zoomed out SEM microscope images. For continuous and closed silver films, the transparency of the electrode, the optical field distribution inside the solar cell, and its power conversion efficiency are strongly increased. Further details can be found in the article by Sylvio Schubert and co‐workers on page 438. [ABSTRACT FROM AUTHOR]

Abstract: We investigate various electrode combinations of bottom and top contacts for organic photovoltaic (OPV) cells. Silver (Ag), indium tin oxide (ITO), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and silver nanowires (AgNW) are used as bottom electrodes. As top electrodes, thin silver layers (t-Ag) and free-standing carbon nanotube (f-CNT) sheets are employed. The manufactured zinc phthalocyanine (ZnPc): fullerene C60 small molecule bulk heterojunction OPV cells with different kinds of bottom electrodes show efficiencies of 1.9∼2.2% and 1.1∼1.5%, when comprised of t-Ag and f-CNT top contacts, respectively. We demonstrate alternative electrodes beyond ITO, silver, and aluminum, which can be readily used for organic photovoltaics technology. [Copyright &y& Elsevier]

Abstract: In this work, we use different encapsulations to protect vacuum-evaporated small molecule organic solar cells with a simple p-i-i-stack for lifetime studies. Our devices use ZnPc and C60 as active materials. Lifetimes (T50) in a range from 300h for un-encapsulated devices to 4000h for glass-encapsulated have been observed. We use a model to distinguish between the water vapor transmission rate (WVTR) of the barrier and an additional WVTR of the aluminum top electrode. For all observed devices a loss of 50% of initial efficiency is observed when 10mgm−2 water entered the device. The losses are related to a reduction of short circuit current density only, whereas open circuit voltage and fill factor remains unaffected. We relate this to an interaction of the water molecules with C60. [Copyright &y& Elsevier]

We report on efficient and stable ITO-free small molecule organic solar cells with conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes using a post-treatment process, causing selective removal of PSS. The solar cells with post-treated PEDOT:PSS electrodes show significantly improved short circuit current densities and efficiencies compared to untreated devices. Moreover, the removal of PSS by the post-treatment significantly improves the lifetime of devices, which are more resistant to loss of fill factor compared to untreated devices. [ABSTRACT FROM AUTHOR]