KEYWORDS: Solar cells, Photovoltaics, Solar energy, Silicon, Perovskite, Manufacturing, Sustainability, Dye sensitized solar cells, Design, Energy efficiency
This report provides a snapshot of emerging photovoltaic (PV) technologies. It consists of concise contributions from experts in a wide range of fields including silicon, thin film, III-V, perovskite, organic, and dye-sensitized PVs. Strategies for exceeding the detailed balance limit and for light managing are presented, followed by a section detailing key applications and commercialization pathways. A section on sustainability then discusses the need for minimization of the environmental footprint in PV manufacturing and recycling. The report concludes with a perspective based on broad survey questions presented to the contributing authors regarding the needs and future evolution of PV.
Tandem or multijunction photovoltaic devices cells offer the clearest path to high efficiency and high areal energy density solar energy conversion. Theoretically and at the laboratory scale, increasing the number of junctions is a simple way to maximize the amount of electricity that can be produced from a small-area device. However, there are multiple approaches to electrically and optically interconnecting the sub-cells in a tandem stack that have different trade-offs in terms of efficiency, cost, and manufacturability. Three terminal (3T) tandems have attracted a great deal of interest at the laboratory scale for their high potential efficiencies and polarity-changing interconnections. However, the coupled nature of 3T devices adds a degree of complexity to the devices themselves and the ways that their performance can be measured and reported. In this talk, I will discuss the recent progress in the field of 3T tandems, including our recently proposed taxonomy for naming 3T devices, experimental demonstrations, robust measurement approaches, and interconnecting 3T cells into strings.
Using the reciprocal space, two types of structures are simple to identify: simple periodic (photonic crystals), which have high diffractive efficiencies but sparse resonances (narrow-band), and random structures, with a continuous reciprocal space (broadband) but suffering from low diffraction efficiencies. A third type, quasirandom structures, lies in between; these provide high diffractive efficiency over a target wavelength range, which is broader than simple photonic crystals but narrower than a random structure. These structures are promising for ultrathin solar cells due to their broader nature. We present our numerical work towards evolving simple photonic crystals in quasirandom structures, and our fabrication approach based on polymer-blend lithography, with initial results on solar cells.
The development of low cost, scalable, renewable energy technologies is one of today's most pressing scientific
challenges. We report on progress towards the development of a photoelectrochemical water-splitting system that will
use sunlight and water as the inputs to produce renewable hydrogen with oxygen as a by-product. This system is based
on the design principle of incorporating two separate, photosensitive inorganic semiconductor/liquid junctions to
collectively generate the 1.7-1.9 V at open circuit needed to support both the oxidation of H2O (or OH-) and the
reduction of H+ (or H2O). Si microwire arrays are a promising photocathode material because the high aspect-ratio
electrode architecture allows for the use of low cost, earth-abundant materials without sacrificing energy-conversion
efficiency, due to the orthogonalization of light absorption and charge-carrier collection. Additionally, the high surfacearea
design of the rod-based semiconductor array inherently lowers the flux of charge carriers over the rod array surface
relative to the projected geometric surface of the photoelectrode, thus lowering the photocurrent density at the
solid/liquid junction and thereby relaxing the demands on the activity (and cost) of any electrocatalysts. Arrays of Si
microwires grown using the Vapor Liquid Solid (VLS) mechanism have been shown to have desirable electronic light
absorption properties. We have demonstrated that these arrays can be coated with earth-abundant metallic catalysts and
used for photoelectrochemical production of hydrogen. This development is a step towards the demonstration of a
complete artificial photosynthetic system, composed of only inexpensive, earth-abundant materials, that is
simultaneously efficient, durable, and scalable.
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