Oxacalix[n]arenes, reassessed members of the calixarene family in which the traditional methylene bridges are replaced by oxygen atoms, have emerged as a promising class of macrocycles in recent years. This tutorial review summarizes the synthetic progress made in the field during the last few years and aims to stimulate its current evolution from a merely synthetic to a more applied branch of macro- and supramolecular chemistry.
1 August 2018 in Solar Energy Materials and Solar Cells
This paper reviews the available life cycle analysis (LCA) literature on organic photovoltaics (OPVs). This branch of OPV research has focused on the environmental impact of single-junction bulk heterojunction polymer solar cells using a P3HT/PC60BM active layer blend processed on semi-industrial pilot lines in ambient surroundings. The environmental impact was found to be strongly decreasing through continuous innovation of the manufacturing procedures. The current top performing cell regarding environmental performance has a cumulative energy demand of 37.58 MJp m−2 and an energy payback time in the order of months for cells having 2% efficiency, thereby rendering OPV cells one of the best performing PV technologies from an environmental point of view. Nevertheless, we find that LCA literature is lagging behind on the main body of OPV literature due to the lack of readily available input data. Still, LCA research has led us to believe that in the quest for higher efficiencies, environmental sustainability is being disregarded on the materials' side. Hence, we advise the scientific community to take the progress made on environmental sustainability aspects of OPV preparations into account not only because standard procedures put a bigger strain on the environment, but also because these methods may not be transferrable to an industrial process. Consequently, we recommend policy makers to subsidize research that bridges the gaps between fundamental materials research, stability, and scalability given that these constraints have to be fulfilled simultaneously if OPVs are ever to be successful on the market. Additionally, environmental sustainability will have to keep on being monitored to steer future developments in the right direction.
Organic photodetectors (OPDs) with a performance comparable to that of conventional inorganic ones have recently been demonstrated for the visible regime. However, near‐infrared photodetection has proven to be challenging and, to date, the true potential of organic semiconductors in this spectral range (800–2500 nm) remains largely unexplored. In this work, it is shown that the main factor limiting the specific detectivity (D*) is non‐radiative recombination, which is also known to be the main contributor to open‐circuit voltage losses. The relation between open‐circuit voltage, dark current, and noise current is demonstrated using four bulk‐heterojunction devices based on narrow‐gap donor polymers. Their maximum achievable D* is calculated alongside a large set of devices to demonstrate an intrinsic upper limit of D* as a function of the optical gap. It is concluded that OPDs have the potential to be a useful technology up to 2000 nm, given that high external quantum efficiencies can be maintained at these low photon energies.
3 November 2017 in Journal of Materials Chemistry A
Organic photovoltaics (OPV) offer a low-cost and esthetically appealing thin-film alternative to the well-known silicon-based solar panels, opening up new applications and markets. A substantial increase in power conversion efficiency (to over 13%) has been achieved for these organic solar cells over the last decade, largely as a result of intensive research on novel electron donor and acceptor materials, combined in a bulk heterojunction device structure. Nevertheless, it is clear that further progress is required to be competitive with more efficient traditional and other emerging thin-film PV technologies. At this moment, the device performance is (among others) limited by the low dielectric constants (εr = ∼3 to 4) of the state of the art photoactive organic materials. Important loss processes inherently connected to the strong coulombic interactions within low-permittivity organic materials can be suppressed through the enhancement of εr. High dielectric constant materials show lower exciton binding energies and hence recombination can be reduced, improving the charge carrier extraction efficiency. Despite these promising prospects, limited research has been devoted to the development and OPV integration of high-dielectric organic semiconductors. In here, an overview is provided of the approaches applied so far to enhance εr of organic compounds specifically developed for OPV purposes, commenting on the insights obtained and the challenges remaining.