Research on perovskites has been ongoing since the 1930s. And as with all aspects of science, the initial work laid the foundation for the monumental advances we are seeing today. The field of perovskite structured materials has seen a bit of revival over the past decade with the incorporation of organolead compounds into titanium dioxide-based solar cells and then as stand-alone solar cells based on perovskite materials. When firms like Lux Research are pontificating on the likelihood of perovskite-based solar cells making an impact on the photovoltaic market, you should take notice.
For researchers active in the field of solar fuels, the transition of perovskite solar cells from the lab bench to the marketplace may not be surprising. However, for those who are not eyebrow deep in the solar fuels literature, this dark horse technology may be coming out of left field. So, let’s take a step back and survey the history and likely impact of perovskites on the field of solar fuels.
Perovskite structured materials take their name from their crystallographic similarities to the mineral “perovskite”, which was discovered by Gustav Rose in 1839 and named after Russian mineralogist L. A. Perovski. The original perovskite, CaTiO3, exemplifies the standard formula for other perovskites – ABX3. Where A & B are typically cations (positively charged) of very different sizes and X is a complementary anion (negatively charged), typically oxygen or a halide (Cl-,Br-, I-). Despite the vast number of combinations available to possibly form a perovskite, only a handful have been successfully incorporated into photovoltaics.
Solar cells made from perovskites are attractive due to their ease of preparation. Compared to silicon-based solar cells, perovskites do not require high temperatures or ultra clean conditions. Ambient laboratory conditions and solution processing capabilities are typically all that are required for perovskite solar cell processing. Despite the facile production methods, stability and reproducibility are a major stumbling block for perovskite solar cells.
Another stumbling block for perovskites is the usual incorporation of lead (Pb) based materials. While new Pb free materials are making their way into the literature, Pb still dominates the perovskite solar cell field, due to its high conversion efficiency – reaching 21%.
Efforts at stabilizing and increasing reproducibility are on-going in the perovskite solar cell field and new reports are published almost daily. If we consider where these novel and exciting solar cells reside in the big picture of photovoltaics, we can see why even Steven Chu, former US Energy Secretary, is excited.
NREL, the National Renewable Energy Laboratory, actively complies a chart of certified photovoltaic performance.
The red circles with yellow fill are perovskites. While a >21% efficiency may seem small compared to the nearly 46% efficiency of the +4-junction solar cells coupled to concentrators, remember that the manufacturing cost of perovskites is significantly less than that of the highly sophisticated and complex 46% efficient cells.
What does this mean for solar fuels? Be it using electrons from perovskite-based photovoltaics to drive electrolyzers or as a direct catalyst material, perovskites have the potential to move us beyond a fossil fuel society and into a renewable fuel marketplace. Given the nearly 4 decade long journey of silicon-based photovoltaics from the lab to consumers rooftops, a few more year of dedication to the field of perovskites may bring exciting advances and innovations.