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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]

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]

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]

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]

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]