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.
While the current solar panel market is still dominated by crystalline silicon solar cells, thin-film solar cell technologies based on chalcogenides are dramatically increasing their market penetration. Apart from device performance, price volatility issues, rare earth elements scarcity issues, and potential environmental issues have raised some concerns about both CdTe and CIGS. A frontrunner in the search for the next generation of thin film photovoltaic materials are low-cost quaternary copper-zinc-tin-sulfide (CZTS) and copper-zinc-tin-chalcogenide (CZTSSe). Notably, these materials are composed of naturally abundant elements in the Earth's crust and have very low toxicity. New research show that there are other chemical routes that use much more benign solvents by demonstrating a simple and facile solution phase method to form CZTS thin film solar cell using commercially available precursors and non-toxic solvents with high yield.
In recent years various bottom-up processes (such as growth techniques) and top-down processes (such as electron beam, lithography, nanoimprint) have been used to produce one dimensional nanostructure on semiconductor substrate. All these approaches involve nanoscale prepatterning or extreme fabrication conditions; hence, they are often limited by associated high cost and low yield. In a novel nanomanufacturing process known as Simultaneous Plasma-Enhanced Reactive Ion Synthesis and Etching (SPERISE), researchers have integrated both nanoscale bottom-up synthetic and top-down etching approach. This eliminates the expensive prepatterning steps and hence give rise to ultrahigh throughput, better reliability, high yield and above all, low cost.
Despites huge research funding for photovoltaics, contribution of solar cells to energy market is still negligible. The major obstacle is high production cost of silicon solar cells: current solar cell market is dominated by silicon technology. Bulky and rigid silicon solar cell with a power conversion efficiency above 10% and a lifetime of 25 years have become the benchmark in photovoltaic industry. However, there are plenty of scopes for disposable and inexpensive solar cells with a moderate efficiency and a shorter lifetime, which can be compared with plant leaves with a typical efficiency of 3-7% and a lifetime less than a year. Here is an example of research that was motivated to produce cheap and disposable solar cells with a moderate power conversion efficiency.
Dye-sensitized solar cells (DSSCs) are among the most promising photovoltaic devices for low-cost light-to-energy conversion with relatively high efficiency. While the DSSC is a fairly mature design, researchers are still trying to improve its efficiency with various techniques. To date, the most commonly used counter electrode in DSSC is fluorine doped tin oxide glass coated with a thin layer of platinum. However, as a noble metal, the low abundance and high cost hinder platinum from being used for large-scale manufacturing. In the quest to seek alternative counter electrode materials for expensive and scarce platinum, a group of scientists has now explored the use of abundant ternary or quaternary materials as potential substitutes for platinum.
Apart from making graphene, graphene oxide itself itself is a fascinating material that has many intriguing properties. Researchers have now developed a graphene-based conductive glue that can function as a metal-free solder for creating mechanical and electrical connections in organic optoelectronic devices. As a proof-of-concept, they fabricated polymer tandem solar cells - multi-junction photovoltaic devices, in which two sub-cells are stacked to achieve higher overall solar absorption - by a direct 'gluing' process. The water-based sticky interconnect and the associated adhesive lamination process could transform the serial layer-by-layer fabrication of tandem devices into a parallel mode, in which the subcells can be independently fabricated and adjusted to balance their photocurrents for achieving high efficiency.
The extremely high electron mobility of graphene - under ideal conditions electrons move through it with roughly 100 times the mobility they have in silicon - combined with its superior strength and the fact that it is nearly transparent (2.3 % of light is absorbed; 97.7 % transmitted), make it an ideal candidate for photovoltaic applications. Recent research suggests, though, that doping is a necessity to harvest the full potential of graphene. The challenge then for researchers is to find suitable fabrication techniques for high-quality graphene flakes that exhibit high charge mobilities. Researchers now present a chemical approach towards non-covalently functionalized graphene, which is generated from vastly available and low-priced natural graphite.
In order to find replacement materials for ITO, scientists have been working with carbon nanotubes, graphene, and other nanoscale materials such as nanowires. While many of these approaches work fine in the lab, upscaleability usually has been an issue. Researchers at Empa, the Swiss Federal Laboratories for Material Science and Technology, have now demonstrated another solution: they presented a transparent and flexible electrode based on a precision fabric with metal and polymer fibers woven into a mesh. The team demonstrated organic solar cells fabricated on their flexible precision fabrics as well as on conventional glass/ITO substrates and found very similar performance characteristics.