Development of ZnO nanowire based CdTe thin film solar cells

This work reports on the development of CdTe thin film solar cells grown on ZnO nanowire arrays. The focus was placed on utilising ZnO nanowire arrays as a replacement to the conventional ZnO thin film buffer layer, thereby requiring minimal alteration to the existing solar cell structure. Incorporation of nanowires was found to alter subsequent film growth and processing, with the nanowire dimensions changing device performance significantly. Shorter, ~100 nm, wires were found to produce particularly low device performance of <0.5% whilst longer wires in the range 250–2000 nm were able to produce more functional cells. Working devices of up to 9.5% efficiency were achieved through the production of “embedded tip” nanowire solar cells. Variation of the nanowires length demonstrated that the nanowires were involved in carrier recombination and that this may be the performance limiting factor

Effect of different photoanode nanostructures on the initial charge separation and electron injection process in dye sensitized solar cells: a photophysical study with indoline dyes

Ultrafast and fast charge separation processes were investigated for complete cells based on several ZnO-based photoanode nanostructures and standard TiO2 nanoparticle layers sensitized with the indoline dye coded D358. Different ZnO morphologies (nanoparticles, nanowires, mesoporous), synthesis methods (hydrothermal, gas-phase, electrodeposition in aqueous media and ionic liquid media) and coatings (ZnO -ZnO core-shell, ZnO-TiO2 core-shell) were measured by transient absorption techniques in the time scale from 100 fs to 100 ps and in the visible and near-infrared spectral range. All of ZnO cells show worse electron injection yields with respect to those with standard TiO2 material. Lower refractive index of ZnO than that of TiO2 is suggested to be an additional factor, not considered so far, that can decrease the performance of ZnO-based solar cells. Evidence of the participation of the excited charge transfer state of the dye in the charge separation process is provided here. The lifetime of this state in fully working devices extends from several ps to several tens of ps, which is much longer than the typically postulated electron injection times in all-organic dye-sensitized solar cells. The results here provided, comprising a wide variety of morphologies and preparation methods, point to the universality of the poor performance of ZnO as photoanode material with respect to standard TiO2. (C) 2015 Elsevier B.V. All rights reserved

Nanomorphology influence on the light conversion mechanisms in highly efficient diketopyrrolopyrrole based organic solar cells

In this work, diketopyrrolopyrrole-based polymer bulk heterojunction solar cells with inverted and regular architecture have been investigated. The influence of the polymer:fullerene ratio on the photoactive film nanomorphology has been studied in detail. Transmission Electron Microscopy and Atomic Force Microscopy reveal that the resulting film morphology strongly depends on the fullerene ratio. This fact determines the photocurrent generation and governs the transport of free charge carriers. Slight variations on the PCBM ratio respect to the polymer show great differences on the electrical behavior of the solar cell. Once the polymer:fullerene ratio is accurately adjusted, power conversion efficiencies of 4.7% and 4.9% are obtained for inverted and regular architectures respectively. Furthermore, by correlating the optical and morphological characterization of the polymer:fullerene films and the electrical behavior of solar cells, an ad hoc interpretation is proposed to explain the photovoltaic performance as a function of this polymer:blend composition

Spray-Pyrolyzed ZnO as Electron Selective Contact for Long-Term Stable Planar CH₃NH₃PbI₃ Perovskite Solar Cells

Electron selective contacts (ESCs) play an important role in the performance of perovskite solar cells (PSCs). ZnO has attracted important attention as a good material for ESCs because of its matched energy levels with those of perovskite, its high transmittance in the visible region, and its high electron mobility. Here we reported the use of ZnO thin layers prepared by spray pyrolysis as ESC for PSCs. Our ZnO based planar CH₃NH₃PbI₃ (MAPbI₃) devices not only were stable in a humidity of 35% but also improved the performance even after more than 1 month of preparation, due to an increase of charge transfer at the ZnO interface as it has been characterized by impedance spectroscopy. The formation of ZnO depends on preparation conditions such as gas flow, zinc acetate solution concentrations, and substrate temperatures, all of which have an effect on the performance of stability of MAPbI₃ solar cells. Also, the low hysteresis reported for these samples was discussed in this study. We have also observed that long-term structural evolution of perovskite film also depends on the ZnO substrate and its deposition method

Passivation of ZnO Nanowire Guests and 3D Inverse Opal Host Photoanodes for Dye-Sensitized Solar Cells

A hierarchical host-guest nanostructured photoanode is reported for dye-sensitized solar cells. It is composed of ZnO nanowires grown in situ into the macropores of a 3D ZnO inverse opal structure, which acts both as a seed layer and as a conductive backbone host. Using a combination of self-assembly, hydrothermal or electrodeposition of single crystalline ZnO nanowires and TiO2 passivation, a novel photoanode with scattering capability for optimal light harvesting is fabricated. © 2014 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim