The light-emitting electrochemical cell promises cost-efficient, large-area emissive applications, as its characteristic in-situ doping enables use of air-stabile electrodes and a solution-processed single-layer active material. However, mutual exclusion of high efficiency and high brightness has proven a seemingly fundamental problem. Here we present a generic approach that overcomes this critical issue, and report on devices equipped with air-stabile electrodes and outcoupling structure that deliver a record-high efficiency of 99.2 cd A−1 at a bright luminance of 1910 cd m−2. This device significantly outperforms the corresponding optimized organic light-emitting diode despite the latter employing calcium as the cathode. The key to this achievement is the design of the host–guest active material, in which tailored traps suppress exciton diffusion and quenching in the central recombination zone, allowing efficient triplet emission. Simultaneously, the traps do not significantly hamper electron and hole transport, as essentially all traps in the transport regions are filled by doping.

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The complex refractive index of a conjugated polymer is measured during electrochemical doping, and the response to p-type and n-type doping is highly asymmetric.

The light-emitting electrochemical cell (LEC) is functional at substantial active-layer thickness, and is as such heralded for being fit for low-cost and fault-tolerant solution-based fabrication. We report here that this statement should be moderated, and that in order to obtain a strong luminous output, it is fundamentally important to fabricate LEC devices with a designed thickness of the active layer. By systematic experimentation and simulation, we demonstrate that weak optical microcavity effects are prominent in a common LEC system, and that the luminance and efficiency, as well as the emission color and the angular intensity, vary in a periodic manner with the active-layer thickness. Importantly, we demonstrate that high-performance light-emission can be attained from LEC devices with a significant active-layer thickness of 300 nm, which implies that low-cost solution-processed LECs are indeed a realistic option, provided that the device structure has been appropriately designed from an optical perspective.

We report on the realization of an ultra-flexible, light-weight and large-area emissive textile device. The anode and active material of a light-emitting electrochemical cell (LEC) were deposited by conformal spray-coating of a transparent fabric-based electrode, comprising a weave of fine Ag-coated Cu wires and poly(ethylene naphthalene) monofilament fibers embedded in a polyurethane matrix. The yellow-emitting textile featured low turn-on voltage (5 V), high maximum brightness (>4000 cd m −2 ), good efficiency (3.4 cd A −1 ), and reasonable lifetime (180 h at >100 cd m −2 ). Uniform emission to the eye was attained from thin and highly flexible textiles featuring a large emission area of 42 cm 2 , without resorting to planarization of the partially wavy-shaped (valley-topeak height=2.7 μm) fabric electrode. The key enabling factors for the functional emissive textile are the characteristic in situ electrochemical doping of LEC devices, the 'dry' spray-sintering deposition of the active material, and the attractive mechanical, electronic and optical properties of the fabric-based electrode.

The light-emitting electrochemical cell (LEC) is a contender for emerging applications of light, primarily because it offers low-cost solution fabrication of easily functionalized device architectures. The attractive properties originate in the in-situ formation of electrochemically doped transport regions that enclose an emissive intrinsic region, but the understanding of how this intricate doping structure affects the optical performance of the LEC is largely lacking. We combine angle- and doping-dependent measurements and simulations, and demonstrate that the emission zone in our high-performance LEC is centered at ~30% of the active-layer thickness ( d al ) from the anode. We further find that the emission intensity and efficiency are undulating with d al , and establish that the first emission maximum at d al ~ 100 nm is largely limited by the lossy coupling of excitons to the doping regions, whereas the most prominent loss channel at the second maximum at d al ~ 300 nm is wave-guided modes.

We present a comprehensive scalar light-scattering model for the optical simulation of silicon thin film solar cells. The model integrates coherent light propagation in thin layers with a direct, noniterative treatment of light scattered at rough layer interfaces. The direct solution approach ensures computational efficiency, which is a key advantage for extensive calculations in the context of evaluation of different cell designs and parameter extraction. We validate the model with experimental external quantum efficiency spectra of state-of-the-art microcrystalline silicon solar cells. The simulations agree very well with measurements for cells deposited on both rough and flat substrates. The model is then applied to study the influence of the absorber layer thickness on the maximum achievable photocurrent for the two cell types. This efficient numerical framework will enable a quantitative model-based assessment of the optimization potential for light trapping in textured thin film silicon solar cells.

Due to the small exciton diffusion length in organic materials, the donor-acceptor heterointerface in simple bilayer solar cells must be placed in close proximity to the bottom electrode. This makes great demands on the planarity of the base layer, since a non-uniform topography can cause adverse shorting through overlying layers. We fabricated indium tin oxide (ITO)/titanium oxide (TiOx)/fullerene (C60)/cyanine dye/molybdenum oxide (MoO3)/silver (Ag) solar cells with TiOx layers deposited via sputtering, coated from a nanoparticle suspension or prepared via a sol-gel process. A power conversion efficiency of 3.7% was measured when using a smooth sol-gel derived TiOx film.