Photovoltaics: Scientists continue to improve the low-cost sun-catching materials
Tapping the near limitless power of the sun with inexpensive solar cells, many scientists believe, will be necessary to meet future global energy needs. Recent advances in photovoltaic devices featuring light-sensitive materials with the perovskite crystal structure and ABX3 stoichiometry—the most studied example is (CH3NH3)PbI3—are bringing such solar cells closer to reality. Commercial solar cells made with high-purity semiconductors such as silicon convert sunlight to electricity with an efficiency of around 25%, but they are costly. Historically, the efficiency of lower cost cells, such as ones based on polymers or quantum dots, started low and climbed slowly, but only reach around 10% efficiency. In contrast, perovskite cells have improved remarkably quickly since 2012, with perovskite progress marching onward in 2014. In a February report on perovskite cells, C&EN noted noted that the top-performing perovskite cell had an efficiency of about 16%. Earlier this month, the National Renewable Energy Laboratory certified a cell from South Korea’s Korea Research Institute of Chemical Technology at 20.1%. Also this year, Northwestern University scientists demonstrated that (CH3NH3)SnI3, an air-sensitive lead-free material that’s normally incompatible with other solar-cell components, can be used to fabricate perovskite cells. The advance avoids concerns regarding lead’s toxicity (Nat. Photonics 2014, DOI: 10.1038/nphoton.2014.82). And at the University of Oxford, researchers showed that including a thin layer of carbon nanotubes embedded in an insulating polymer improves perovskite cell resistance to humidity and thermal degradation (Nano Lett. 2014, DOI: 10.1021/nl501982b).