Graphical Abstract The Front Cover shows an artistic representation of a rack of sunlight-powered artificial leaves recycling the carbon dioxide produced in chemical processes into syngas. In their Research Article, T. Merdzhanova, J. Pérez-Ramírez and co-workers demonstrate that artificial leaves can provide variable CO:H2 ratios in the range 1.8–2.3 on demand and maintain a near-optimal efficiency when the electrolyte flow is considered as a design variable. This facilitates the connection of a-leaves with downstream technologies requiring accurate syngas compositions such as Fischer–Tropsch synthesis or anaerobic fermentation.

Invited for this month's cover is the group of Javier Pérez-Ramírez at ETH Zürich, which collaborated with the group of Tsvetelina Merdzhanova at Forschungszentrum Jülich. The image shows how artificial leaves, able to recycle carbon dioxide into syngas of variable composition, could be integrated with chemical plants. The Research Article itself is available at 10.1002/cssc.202301398.

Multijunction solar cells, proven technological route for achievements of highest PV conversion efficiencies, require accurate tuning of the sub-cell absorption to ensure that every cell in the stack delivers the same current density. Even though currents of the sub-cells can be precisely matched for a fixed illumination spectrum, current mismatch cannot be avoided in real terrestrial applications due to variations of the irradiance spectrum. The issue becomes critical when a solar cell has to cover wider range of applications such as a mixture of direct sun / shadow / artificial light - the case for various distributed PV-powered electronics. Furthermore the current matching constrains choice of materials and designs of sub-cells for a tandem device. A straightforward basic configuration with decoupling the sub-cell's currents is a 3-terminal configuration with one additional contact sheared by the top and bottom cell. This concept requires voltage-matching between the top and bottom cell when these cells are integrated in modules. A realistic concept for the voltage-matched 3-terminal cell reported recently includes a wide gap top cell combined with a tandem bottom cell made of 2 sub-cells with lower bandgaps. The concept is a hybrid between 2 and 3-terminal configurations with voltage matching and relaxed current matching constrains. Established thin film silicon solar cell technology provides interesting option to realize the hybrid 3-terminal cell with amorphous Si top cell (V-OC approximate to 0.9 V) and two microcrystalline Si cells (V-OC approximate to 0.5 V). In this work we present proof of concept of the voltage matched 3-terminal tandem cell prepared with highly transparent and conductive IOH intermediate contact. The efficiency of 10.4% has been achieved made up of independently operating 7.9% efficient top cell and 2.5% efficient bottom tandem cell. The paper summarizes the development and discusses optical losses identified in the 3-T devices.

ABSTRACTThin‐film silicon solar cells often rely on a metal back reflector separated from the silicon layers by a thin rear dielectric as a back reflector (BR) design. In this work, we aim to obtain a better insight into the influence of the rear‐dielectric/Ag BR design on the optical performance of hydrogenated microcrystalline silicon (µc‐Si:H) solar cells. To allow the application of a large variety of rear dielectrics combined with Ag BRs of diverse topographies, the solar cell is equipped with a local electrical contact scheme that enables the use of non‐conductive rear dielectrics such as air or transparent liquids of various refractive indices n. With this approach, detached Ag BRs having the desire surface texture can be placed behind the same solar cell, yielding a direct and precise evaluation of their impact on the optical cell performance. The experiments show that both the external quantum efficiency and the device absorptance are improved with decreasing n and increasing roughness of the BR. Calculations of the angular intensity distribution of the scattered light in the µc‐Si:H are presented. They allow for establishing a consistent picture of the light trapping in the solar cell. Copyright © 2013 John Wiley & Sons, Ltd.

In this work, we report on the fabrication of microcrystalline thin-film silicon solar cells on textured glass substrates. The development of transparent and conductive front contacts for these solar cells is presented. State-of-the-art random textures for light-trapping were replicated into a glass-like resist on glass substrates with an imprint process. We applied an industrial relevant soft polymer mold that gives excellent replication accuracy. The necessity of applying thin front contacts for enhanced incoupling of the incident light is shown. An increased series resistance of these thin front contacts caused a decrease of the fill factor of the solar cells. One way to surpass this decrease in fill factor by reducing the solar cell width is demonstrated. In addition, the light-trapping and the light-incoupling for solar cells deposited on three different types of random textures were compared. (C) 2013 Elsevier B.V. All rights reserved.

Thin-film silicon solar cells often apply a metal back reflector (BR) separated from the silicon layers by a thin rear dielectric of thickness around 80nm or a white paint combined with a thick rear dielectric of several micrometers. In this work, we investigate the optical performance of microcrystalline silicon (μc-Si:H) solar cells applying BRs of various topographies. In contrast to a standard 80nm-ZnO/Ag BR design, for which the BR nearly strictly follows the texture of the underlying μc-Si:H layers, placing the Ag BR far from the μc-Si:H layers allows for a variation of the BR topography. Irrespective of the investigated BR topographies and also for a conventional white paint BR, long distances (of several micrometers) between the BR and the μc-Si:H layers are found to be detrimental for the light trapping. Optical simulations based on both rigorous and scalar scattering theory have been performed to understand the impact of the diverse BR designs on the optical cell performance.

This work presents as-grown textured ZnO:Al films by rf magnetron sputtering initiated by pre-treatment of glass substrate with mixed argon and oxygen ions. A 650nm thick of this film exhibits surface texture features with lateral size around 500nm; the resistivity is below 5×10−4Ω·cm and the transparency in the near-infrared spectral range is high (>80% at 1000nm). Microcrystalline silicon thin film solar cells grown on the textured glass exhibit excellent light trapping effect with a short circuit current density of 18.2mA/cm².

We present a precise and flexible method to investigate the impact of diverse detached reflector designs on the optical response of p–i–n thin‐film silicon solar cells. In this study, the term detached reflectors refers to back reflectors that are separated from the silicon layers by an intermediate rear dielectric of several micrometers. Based on the utilization of a highly conductive n‐doped layer and a local electrical contact scheme, the method allows the use of non‐conductive rear dielectrics such as air or transparent liquids. With this approach, diverse combinations of back reflector and rear dielectric can be placed behind the same solar cell, providing a direct evaluation of their impact on the device performance. We demonstrate the positive effect of a rear dielectric of low refractive index on the light trapping and compare the performance of solar cells with an air/Ag and a standard ZnO/Ag back reflector design. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Textured glass is prepared by ion beam treatment using wet chemically etched ZnO film as three dimensional etching mask. The shape and rms roughness of the textured glass can be adjusted by changing the initial ZnO thickness, wet-chemical etching duration and ion beam etching parameters. The maximum rms roughness we achieved is 228 nm, with lateral feature size larger than 2 mu m. The glass texturing process allows to study scattering already at the glass/TCO interface to enhance the refractive index step from rough material to silicon. First microcrystalline silicon thin film solar cells grown on the textured glass reveal certain light trapping effect with a short circuit current density up to 20 mA/cm(2). (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The performance of multijunction amorphous silicon-based thin film solar cells has been reported using thin layers of TiO2 and SiOx acting as refractive index matching optical layers for different interfaces of the superstrate device structure. Improvement of short-circuit current from the sub-cells of a-Si/μc-Si cells is demonstrated with TiO2 as anti-reflection layer at TCO/Si interface and SiOx as intermediate-reflector layer between two sub-cells. An initial efficiency of 11.8% is achieved by applying both the TiO2 and SiOx optical layers in a-Si/μc-Si solar cell.

In this paper we explore the efficiency potential of a-Si/µc-Si tandem cells that are produced under conditions that lead to a considerable production cost reduction. On standard lab-type texture-etched ZnO:Al, 1 cm² a-Si:H/µc-Si:H tandem test cells on a deposition area of 30 x 30 cm² were made that showed an initial efficiency of 9.9%, whereas the total deposition time of intrinsic layers was only 22 minutes. The silicon thickness is only 600 nm. On high-rate texture-etched ZnO:Al an efficiency of 9.4% initial was reached. Standard light-induced degradation experiments showed a degradation rate of only 5 to 8% after 1000 hours. The regime of very short preparation times

We have investigated the contribution of localized surface plasmon polaritons (LSPPs) in silver nanoparticles with radii smaller than 20 nm to the photocurrent of ultrathin photosensitive devices based on amorphous silicon. An increased light absorption and an enhanced photocurrent are found for wavelengths between 600 nm and 1150 nm in presence of nanoparticles. As amorphous silicon absorbs light efficiently only at wavelengths up to 750 nm, the increased photocurrent in the near infrared range is explained in terms of LSPP-induced photoemission of electrons within and in close vicinity of the nanoparticles.

Hydrogenated microcrystalline silicon (μc-Si:H) has lately attracted considerable attention as a promising candidate for thin-film transistors (TFTs) in large area electronic applications due to its superior charge carrier mobility. Here, we present ambipolar TFTs and inverters based on microcrystalline silicon prepared by plasma-enhanced chemical vapor deposition at low deposition temperature of 160°C. The electrical parameters of the ambipolar microcrystalline silicon TFTs and inverters will be described. The influence of contact effects on the operation of ambipolar microcrystalline silicon TFTs was investigated. Furthermore, the influence of the ambipolar transistor characteristics on the performance of the ambipolar inverter will be discussed.

Aluminum doped zinc oxide (ZnO:Al) films were prepared by high rate magnetron sputter deposition either in reactive or non reactive mode from metallic or ceramic targets, respectively. These two different sputtering modes were compared in view on industrial scale production. We characterized the electrical properties in dependence on deposition parameters and growth rate. The deposition pressure dependence and statically deposited ZnO:Al films revealed a strong influence of high energy ion bombardment, which reduces conductivity and thus has to be avoided by appropriate deposition conditions. Finally, texture-etched ZnO:Al films were successfully applied as front contacts for silicon thin film solar cells. An initial aperture area (676 cm2) module efficiency of nearly 10 % was achieved for a-Si:H/μc-Si:H tandem modules for both ZnO:Al preparation processes.