There are a number of interesting technologies being developed and commercialized for photovoltaics (PV). Crystalline silicon, cadmium telluride (CdTe), amorphous silicon (aSi), copper indium gallium diselenide (CIGS), dye sensitized solar cells (DSSC) and organic photovoltaics (PV) have all drawn attention for the potential they have for producing energy. Each of these are at various stages of commercialization, with crystalline silicone and CdTe leading the way.

Perovskite is a thin-film solar technology that is drawing a lot of attention in the PV field. Named after a mineral discovered by Gustav Rose in the Ural Mountains in 1839, perovskite is named after the Russian mineralogist Count Lev Perovski. The actual chemical composition is calcium titanate. However, it is the structure of the PV cell, and not the composition of it, that lends this new solar cell its name. Prof. Henry Snaith ignited the global interest in perovskites when he published a seminal paper in “Science” in October 2012, since then more than 350 papers have been published.

“The ‘perovskite’ behind the new photovoltaic technology only shares the crystal structure with the mineral perovskite – in fact in contains neither calcium, titanium nor oxygen,” said Dr. Chris Case, chief technology officer at Oxford PV, a leader in this technology. “However, the perovskite structure is quite versatile, and the electronic and optical properties can be modified by substituting different cations and anions.

“Perovskite structured materials are engineered materials that include BaTiO3, LaGaO3 and such important electronic compositions as BaTiO3 – and have applications from high temperature superconductors to piezoelectrics,” Dr. Case added. “The perovksite formulation that has been behind this PV activity is a mixture of lead iodide and methyl ammonium.”

The perovskite is built into a structure that looks very much like a planar, thin-film semiconducting heterojuction, and only requires electron and hole extraction layers and contacts on either side of the semiconducting layer.

“Any good solar absorber needs certain characteristics – it must absorb well across the visible spectrum, the photocarriers that are generated should have long lifetimes and high mobility and of course it needs to be inexpensive,” Dr. Case noted. “The particular perovskite solar absorber being commercialized by Oxford PV has all of those characteristics. In fact, after GaAs, it probably is the material with the highest potential solar energy conversion efficiency.”

The key drivers for perovskite solar cells are the abundance of raw materials and the ability to produce it through low-cost solution processing.

“The earth abundance of the raw materials and the fact that the solar absorber can be deposited by low-cost low temperature solution processing are key advantages to perovskites over all other identified solar materials, especially mainstream conventional silicon, which requires expensive high temperature/energy steps to purify and utilize,” Dr. Case said.

What is really impressive about perovskite is the efficiencies it is recording. Typically, a new technology requires decades to reach high single digits; in the past five years, efficiencies have reportedly jumped from 4% to 19%.

“Single junction perovksite cells already near 20% should exceed 20% this year, and with a theoretical efficiency over 30%, there is no reason not to expect devices to exceed 25%,” Dr. Case said. “Perovskite on silicon tandem cells should be able to raise the overall efficiency by 20% (relative).”

Oxford PV and Perovskite

Oxford PV is among the leaders in the perovskite field. Prof. Snaith and CEO Kevin Arthur founded Oxford PV in 2009 with the goal of commercializing Prof. Snaith’s expanding portfolio of DSSC patents. The initial target market was decorative glazing products for building integrated photovoltaic (BIPV) applications.

However, the company changed its focus in 2013, suspending its DSSC operations and dedicating its resources to the commercialization of perovskite solar cells for BIPV glazing products and hybrid Si/perovskite and CIGS/perovskite tandem cells for mainstream solar markets. The company received seed funding in June 2011, and has since raised a total of $11 million from a mixture of equity and grant funding. The company is currently raising a series ‘B’ investment round of $12 million.

“With a technical staff of 30 in-house scientists dedicated to commercializing the technology and supported by 20 researchers at Professor Snaith’s laboratory, Oxford PV has a substantial position,” Dr. Case said. “Oxford PV has the exclusive license to the key IP from Snaith’s laboratory, and is committed to delivering both BIPV and tandem technology to partners via a licensing model.”

Dr. Case sees a two-fold path to commercialization for perovskite and for Oxford PV, both through tandem cells as well as BIPV, and he is optimistic about the potential for the technology.

“Oxford PV will license a technology package to silicon wafer/silicon panel manufacturers interested in building tandem cell technology into their products,” Dr. Case said. “The BIPV technology will also be licensed to building glazing providers and glass finishers for installation for into large commercial structures. Materials supply will be carried out by accredited chemical production partners.

“By 2023, we expect to have achieved at least 6% market share of the BIPV product and will also have been successful in the licensing of the tandem architecture to many advanced silicon cell partners,” Dr. Case concluded. “The ITRPV roadmap shows the adoption rate of n-type silicon cells going forward, and we expect our business growth to mimic that rate.”