Graphene-based nanomaterials have many promising applications in energy-related areas. In particular, there are four major energy-related areas where graphene will have an impact: solar cells, supercapacitors, lithium-ion batteries, and catalysis for fuel cells. Graphene could be a promising replacement material for indium tin oxide. A recent review provides an overview of research on graphene and its derivatives, with a particular focus on synthesis, properties, and applications in solar cells.
There is currently a tremendous amount of interest in the solution processing of inorganic materials. Low cost, large area deposition of inorganic materials could revolutionize the fabrication of solar cells, LEDs, and photodetectors. The most common methods currently used for film formation are spin coating and dip coating, which provide uniform thin films but limit the geometry of the substrate used in the process. The same nanocrystal solutions used in these procedures can also be sprayed using an airbrush, enabling larger areas and multiple substrates to be covered much more rapidly. The trade-off is the roughness and uniformity of the film, both of which can be substantially higher. Researchers have now attempted to quantify these differences for a single-layer solar cell structure, and found the main difference to be a reduction in the open circuit voltage of the device.
Using quantum dots as the basis for solar cells is not a new idea, but attempts to make such devices have not yet achieved sufficiently high efficiency in converting sunlight to power. Although these performance levels are promising, all high-performing device results to date have relied on a multiple-layer-by-layer strategy for film fabrication rather than employing a single-layer deposition process. Now, though, researchers have developed a semiconductor ink with the goal of enabling the coating of large areas of solar cell substrates in a single deposition step and thereby eliminating tens of deposition steps necessary with the previous layer-by-layer method.
Organic solar cells are regarded as an emerging technology to become one of the low-cost thin-film alternatives to the current dominating silicon photovoltaic technology, due to their intrinsic potential for low-cost processing (high-speed and at low temperature). However, it is generally believed that the PCE needs to be improved to above 10% in order for organic solar cells to become truly competitive in the marketplace. Currently, the best reported PCE, achieved in laboratories, lies in the range of 6.7% to 7.6% for molecular, and 8.3% to 10.6% for polymeric OPVs.
Many researchers are investigating the development of flexible solar cells in hopes of improving efficiency and lowering manufacturing costs. As an important member of the organic photovoltaics family, polymer solar cells draw the most research interest, due to the relatively high power conversion efficiency achieved. However, compared to the high efficiencies of inorganic solar cells, the best polymer solar cells still show a lower efficiency. Improved nanomorphology is seen as key to improving the efficiency of organic solar cells. One particular nanotechnology approach would use nanoimprint lithography to produce precisely nanostructured devices rather than using chemical methods of manufacturing.
Energy-relevant materials like selenium have photovoltaic and photoconductive properties that make them interesting for the manufacture of solar cells and lighting devices. In most of these applications, as with all nanomaterials, the material surface plays a critical role. Therefore, their surface properties, and more particularly their solid surface energy - the energy required to create a new surface - have to be carefully determined in order to fully understand and control relevant manufacturing parameters for devices based on these materials.
It was previously thought that carbon nanotubes and other carbon nanomaterials are not well suited to make efficient solar cells. The main reason for this is that nanotubes are hard to isolate in single chiralities or in a given diameter range and only of semiconducting or metallic type, and thus it is hard to use them in a controlled way. New work has now shown that thin film solar cells made entirely out of carbon nanomaterials can achieve an efficiency similar to that of polymer solar cells at their initial research stages (a decade ago), but with much improved photostability. As a result, the use of carbon materials holds great promise towards the realization of photostable thin film solar cells.
The significant research interest in the engineering of photovoltaic (PV) structures at the nanoscale is directed toward enabling reductions in PV module fabrication and installation costs as well as improving cell power conversion efficiency. With the emergence of a multitude of nanostructured photovoltaic device architectures, the question has arisen of where both the practical and the fundamental limits of performance reside in these new systems. A particular advantage of nanostructured materials is the tunability of their optical and electronic properties, which enables improved PV power conversion efficiencies by implementing strategies for reducing thermal losses. A recent review article addresses the limits to the performance of molecular, organic, polymeric, dye-sensitized, and colloidal quantum dot-based solar cells.