Research: Next-Generation Photovoltaic Technologies

Postdoctoral appointees Ioan Botiz (left), Karen Mulfort, and researcher Alex Martinson are exploring the possibilities for coupling solar fuel and photovoltaic devices.

Most commercial solar cells (photovoltaics) are made from a highly purified silicon crystal, similar to the material used in the production of computer processors. The high cost and complex production process of these silicon solar cells has generated interest in developing alternative photovoltaic technologies. Newer materials entering the marketplace include cadmium telluride (CdTe) and copper indium gallium selenide (CIGS). These materials have lower costs and simpler fabrication processes, but each relies on a material that is rare on the Earth (tellurium or indium). Though not a concern in the immediate future, the scarcity of these source materials will ultimately limit the scale at which these technologies can penetrate the market.

Organic solar cells are a promising next-generation technology because they are synthesized from abundant materials (small molecules or polymers) that can typically be processed using low-cost and scalable techniques. Moreover, polymer solar cells are lightweight, mechanically flexible, potentially disposable, and have lower potential for adverse environmental impact. Today, though, there are also significant disadvantages of polymer solar cells. They have lower efficiency and generally degrade when exposed to real-world environmental conditions for extended periods. Hybrid solar cells combine advantages of both organic and inorganic materials. Hybrid photovoltaics use polymers or other organic molecules to absorb light and, in some cases, to transport holes; inorganic materials in a hybrid solar cell transport the electrons. These cells have a potential for higher efficiency than purely organic cells, though the current efficiencies are still too low to be commercially viable on a large scale. There are also opportunities to use fully inorganic systems that are based on plentiful materials, where efficiencies can be improved by carefully controlling the structure on extremely small length scales. To fully realize the potential of these various types of next-generation solar cells, it is critical to perform both basic and applied research into new technologies.

Highlights
	Trace impurities in organic photovoltaics
	Stabilizing efficient photovoltaics from earth-abundant materials
	Rethinking the idealized morphology in high-performance organic photovoltaics
	A new understanding of organic semiconductor junctions
	Enhancing low power conversion efficiency in organic photovoltaic cells
	Enabling efficient photovoltaics from earth-abundant materials
	Commercialization of low-cost nanostructured solar cells
	"Homegrown" hybrid solar cell aims for low-cost power
	Creating ideal structures for photovoltaics using block copolymers
	Computational modeling of polymers for solar cells
	Deciphering uncertainties in the cost of solar energy
	New inorganic semiconductor layers hold promise for solar energy

May 2013