• Energy Research

We report a detailed study on the operating principles of silver nanowire (Ag NW) networks as a transparent conducting electrode. Current limitations to achieve high conversion efficiencies are overcome with the combination of Ag NW and specifically designed ZnO nanoparticles (NP). The new transparent electrode presents improved optoelectronic properties with respect to the most widely used ITO—indium tin oxide. We demonstrate that there are non-conducting void spaces left between neighboring nanowires onto the holding substrate as a consequence of processing the Ag NW film from a solvent dispersion. Moreover, the fabrication of efficient ITO-free organic solar cells (OSC) based on Ag NW relies on filling the resulting void spaces with a highly selective and conductive supporting thin layer. This slight modification of the Ag NW film enables the great majority of photogenerated charge carriers – that would otherwise be recombined at voids – to be efficiently collected by the nanowires. In this way, we report – to our knowledge – one of the highest ITO-free OSC (3.8%) also fabricated onto flexible substrates (3.2%) with commercially available Poly (3-Hexylthiophene) (P3HT) and Phenyl-C61-butyric acid methyl ester (PCBM). This breakthrough could once and for all bring the potential of flexible low-cost organic photovoltaics into reality.

Abstract Photovoltaic modules were manufactured by vacuum resin infusion process using glass reinforced epoxy composite as encapsulant where the cells are embedded. Incorporation of ultraviolet absorber (UVA) and hindered amine light stabilizer (HALS) additives to the epoxy resin was studied, given their potential to enhance the performance stability of the modules under ultraviolet (UV) radiation exposure. Photovoltaic and aging performance were examined through the evolution of external quantum efficiency (EQE) spectra, short-circuit current values and colour change. Decrease in the initial photovoltaic performance of the modules was observed, as evidenced in the short-circuit losses when additives are incorporated. Regarding the performance stability, increasing the content of both, UVA and HALS, leaded to improved results with lower short-circuit current loss and yellowness observed due to UV radiation. The most stable module, with cells embedded in 1% UVA and 1% HALS containing composite, showed a 2.8% short-circuit current loss after an UV exposure of 15.4 KWh/m2. UV protection enhancement was obtained in trade-off with initial photovoltaic performance, which should be considered when defining the additives and the amount to be used.

We report azafullerene monoadduct DPC59N, which in organic solar cells outperforms benchmark acceptor PC60BM in respect to JSC and EQE.

Herein, we studied the use of two different Self Assembled Monolayers (SAMs) made of semiconductor hole transport organic molecules to replace the most common p-type contact, PEDOT:PSS, in PiN methyl ammonium lead iodide perovskite solar cells (PSCs).

Two new perylenediimides (PDIs) have been developed for use as electron acceptors in solution-processed bulk heterojunction solar cells. The compounds were designed to exhibit maximal solubility in organic solvents, and reduced aggregation in the solid state. In order to achieve this, diphenylphenoxy groups were used to functionalize a monomeric PDI core, and two PDI dimers were bridged with either one or two thiophene units. In photovoltaic devices prepared using PDI dimers and a monomer in conjunction with PTB7, it was found that the formation of crystalline domains in either the acceptor or donor was completely suppressed. Atomic force microscopy, X-ray diffraction, charge carrier mobility measurements and recombination kinetics studies all suggest that the lack of crystallinity in the active layer induces a significant drop in electron mobility. Significant surface recombination losses associated with a lack of segregation in the material were also identified as a significant loss mechanism. Finally, the monomeric PDI was found to have sub-optimum LUMO energy matching the cathode contact, thus limiting charge carrier extraction. Despite these setbacks, all PDIs produced high open circuit voltages, reaching almost 1 V in one particular case.

In the operation & maintenance (O&M) of photovoltaic (PV) plants, the early identification of failures has become crucial to maintain productivity and prolong components' life. Of all defects, cell-level anomalies can lead to serious failures and may affect surrounding PV modules in the long run. These fine defects are usually captured with high spatial resolution electroluminescence (EL) imaging. The difficulty of acquiring such images has limited the availability of data. For this work, multiple data resources and augmentation techniques have been used to surpass this limitation. Current state-of-the-art detection methods extract barely low-level information from individual PV cell images, and their performance is conditioned by the available training data. In this article, we propose an end-to-end deep learning pipeline that detects, locates and segments cell-level anomalies from entire photovoltaic modules via EL images. The proposed modular pipeline combines three deep learning techniques: 1. object detection (modified Faster-RNN), 2. image classification (EfficientNet) and 3. weakly supervised segmentation (autoencoder). The modular nature of the pipeline allows to upgrade the deep learning models to the further improvements in the state-of-the-art and also extend the pipeline towards new functionalities. 16 pages, 14 figures

We report organic photovoltaic devices in which the standard ITO transparent electric contact has been substituted by lower cost ultrathin metallic electrodes. Solution and vacuum processable n and p-type semiconductors provide the electrode with the rectifying behavior of the diode. We are in this way able to invert the built-in electric field at wish and make the device deliberately either top or bottom sensitive with the same efficiency depending on the application. Taking advantage of these new generation electrodes we furthermore report devices with fill factors over 70%—to our knowledge, the largest published to date for an organic photovoltaic cell—and power conversion efficiencies over the state-of-art with 3.5% in inverted P3HT:PCBM devices, ITO free designs over 2.5% and (semi)transparent photovoltaic devices with conversion efficiencies close to 2.6%. This breakthrough could once and for all trigger the fabrication of organic tandem solar cells and photovoltaic windows.