As in previous years, the international Photovoltaics (PV) community met at PhotoVoltaic Technical Conference 2016, PVTC, which is the 7th event of a series of international PV specialty conferences taking place in South France. This year, for the first time, the chosen location was Marseille from 9 to 11 May 2016 at the International Center of Villa Méditerranée. The meeting put together more than 100 delegates from all around the world representing over 20 countries (Algeria, Australia, China, France, Germany, Italy, Japan, Morocco, Poland, Spain, Switzerland, USA, Tunisia, etc.) on the topic “From materials and advanced processes to innovative applications.” This year, the conference put a special focus on Mediterranean projects. For example, the NOOR power plant and the Moroccan solar plant were presented by the Moroccan Agency of the solar energy (MASEN), while the Research Institute on the Energy and the Environment of Qatar reviewed the reliability and the performances of PV in Qatar.
High quality scientific and technical presentations, from both academic and industrial sectors, in the form of oral presentations, flash talks, and poster contributions, were presented in the conference. In particular, interesting applications such as transparent glazing PV (Crosslux, Southern France), solar roads (Aximum), solar veils (Solar Cloth System, Southern France), portable objects (SunPartner Technologies, Southern France), the PV floating off Marseille (ASI-Innovation), solar stained-glass window style Mondrian (University of Utrecht, The Netherlands), of the colored glass BIPV (CSEM, Switzerland), and the design of solar objects were presented.
This special issue contains a compilation of five of the most relevant contributions to the conference, which attracted much attention from the participants. The selected papers shown here are an example of the diversity of topics and the multidisciplinary character of PV, in particular, when new applications are to be developed.
Although PV power plants have been (and will continue to be) under development, the vision to use Photovoltaics (PV) as a decentralized and sustainable source of energy is growing between PV communities. This decentralized vision takes not only the form of a distributed energy production environment but also the form of a multitude of products such as devices, vehicles, wearables, and buildings. However, today, the development of photovoltaic modules is still primarily driven by the idea of economies of scale, which leads to unvarying PV modules suitable for large-scale power plants. These products are not fully suitable for their integration into building skins, roof tiles, or electric and even less in portable/wearable devices. However, a growing number of designers, architects, and industrial manufacturers across the world share a common interest in using photovoltaics in a flexible and customized way, looking for aesthetics, flexibility, and portability. In this sense, Adamovic et al.1 discuss the interest and potential future applications of new flexible production processes and materials, which could lead to PV modules whose characteristics can be modified “on-the-fly.” In particular, an interesting approach based on a novel manufacturing process of PV thin film modules is presented. This new approach allows adjusting the electrical properties of a given PV module on-the-fly as well as the production of fully customized photovoltaic modules with respect to their size, shape, and patterns. Combined with an optimized solar cell performance, the pliability given by the flexible substrate and the encapsulation of these novel PV modules provide the necessary variability and performance ability for design-driven solar solutions. A custom designed PV material opens up for an entirely new market and ranges of products within high levels of design under competitive prices.
Based on these properties, CIGS (Cu(In,Ga)(Se,S)2) is presented as a main candidate for addressing the new market opportunities opened by flexibility and customization. However, to fully satisfy these market requirements, the outdoor behavior and reliability issues should be considered. In this sense, Theelen et al.2 perform a comparative and systematic study of the impact of exposure of CIGS cells and modules to temperatures varying from room temperature (25 °C) to elevated temperatures (105 °C). The interest of this work lies on the comparison of flexible (on polyimide substrates (PI)) and rigid (glass substrates (SLG)) devices. They show that the open circuit voltage declined as a function of temperature with an absolute value similar for all the cells regardless of the substrate. The short circuit current density showed an expected small increase with temperature for PI samples, while it decreased for most SLG devices. The authors propose that this decrease is largely caused by enhanced recombination. Additionally, they observe a small decrease in the series resistance for most devices, while the shunt resistance showed a large decrease with increasing temperature. The fill factor and efficiency therefore also showed a decrease with temperature. The understanding of the difference in the origin will be critical for the future credibility and bankability of future potential markets.
Another critical issue for the development of flexible, lightweight customizable devices is the development of suitable transparent conducting materials (TCMs), which is a more important fabrication process compatible with roll-to-roll fabrication. In particular, in the context of new generation solar cells, the ability to design low-cost, low-temperature, roll-to-roll compatible fabrication methods is a key factor to render such PV alternatives more competitive. Nguyen et al.3 provide an overview of a novel Spatial-Atomic Layer Deposition approach. The use of Atmospheric Pressure Spatial Atomic Layer Deposition (AP-SALD) has gained popularity in the last decade. The success of this technique relies on the possibility to deposit thin films in a fast, vacuum-free, low-cost, low-damage, and high throughput way.
The authors present an interesting approach in a homemade AP-SALD system where they show a high uniformity, conformity, and crystallinity. Both ZnO and AZO (particularly suitable for CIGS) films present a high transparency of 80%–90% in the visible range. In the case of AZO, a significant increase in carrier density from 3 × 1019 cm−3 to 4.25 × 1020 cm−3 results in a minimum resistivity of 5.57 × 10−3 Ω cm, comparable to reported values.4 The carrier density of the AZO film deposited by AP-SALD can even reach 7.5 × 1020 cm−3, which is higher than the previous results reported in the literature for both conventional and spatial ALD.4 In the case of an undoped ZnO layer (which is used in many CIGS devices), the optical band-gap can be tuned by varying the deposition temperature. Concerning electrical properties, optimized ZnO films exhibit a resistivity of 5 × 10−2 Ω cm.
Considering the same market approach and targeting the same kind of device where the main characteristics are flexibility and customization, Saranin et al.5 detail the characteristics of a novel type of tunable organic photovoltaic (OPV) tandem device with ionic gating by in-situ ionic liquids. These devices are comprised of two solution‐processed polymeric OPV cells connected in parallel by a dry‐laminated transparent multiwall carbon nanotube (MWCNT) interlayer. The MWCNT interlayer of these 3‐terminal tandem devices play the role of a common electrode with a Fermi level that can be tuned via ionic gating to turn it into a common cathode, collecting photogenerated electrons from both the sub‐cells. Ionic gating employs electric double layer charging of MWCNTs in order to lower the work function of the common CNT electrode and increase its n‐type conductivity. These tandem devices are fabricated in ambient conditions via dry‐lamination of MWCNT transparent sheets. The results demonstrate different regimes of ionic gating at low, medium, and high gating voltages Vgate and show optimal doping of MWCNTs. The doping of PCBM and polymers is additionally confirmed by the change in the charging and discharging current dynamics at high Vgate above the threshold. Although OPV still lacks efficiency and reliability demonstrations, its potential is highly relevant.
A final application relevant to PV and its intrinsic need for electricity storage solution6 which also addresses the decentralized future of PV deployment is the solar hydrogen technologies. The urgent need for clean and renewable energy has stimulated considerable interest in developing solar hydrogen technologies either by combining photovoltaics with water electrolysers or by constructing photoelectrochemical cells (PECs).7 Kravets et al.8 show that the production of hydrogen through water splitting via photocatalysis seems to be a promising and appealing pathway for clean energy conversion and storage. Their work shows, for the first time, a series of metallic binary alloyed superconductors (MgB2, AlB2, NbB2, and NbSe2) that can be used as photoanodes and cathodes in a photocatalyst composite for both hydrogen production and water oxidation reactions. Interestingly, they describe that the highly active ion binary metal-based photocatalyst can be used as a low-cost alternative to Pt for water photolysis. The metallic binary alloyed superconductors exhibit high activity toward both the oxygen and hydrogen evolution reactions in pure distilled and sea water. The combination of the two such photoanodes and cathodes yields a water splitting photocurrent density of around 1 mA/cm2, corresponding to a solar-to-photocurrent efficiency of 34%. A strong correlation between the values of superconductive temperature and photocatalytic water splitting efficiency for investigated diborides has also been revealed.
This edition of PVTC 2016 contributed to feeding the need for the development/creation of new markets and the associated technical solutions for PV. This should not only contribute to the consolidation of a bright future PV industry but also to address many of the present issues for PV large-scale integration. Decentralized solutions, associated with more flexible production and materials, together with the adequate technical developments, for electricity storage are an important step towards future energy panorama.
