Of all the current methods of using photovoltaics to convert sunlight into electricity, the most advanced are those based on silicon. It may not be as cheap and durable as polymer and thin film solar cells, but it is already reaching high efficiencies, and researchers at Ecole Polytechnique Fédérale de Lausanne have set a new record of 22.4%. This was accomplished with a hybrid approach to the solar cell's design.
Starting with a p-doped crystalline cell, the commonest and cheapest of silicon solar cells, the researchers coated the cell with a ten nanometer layer of amorphous silicon. The interaction between these two different layers allowed that cell to reach 21.4% efficiency, which is up from the 18-19% record achieved for monocrystalline cells. The impressive 22.4% was reached with a different and less common substrate.
With this hybrid or heterojunction approach, we may see arrays capable of powering a four-person home from just $2500 worth of solar cells. Already a company is working to commercialize this technology and in three to five years they expect the production costs to be $100 per square meter.