Hand-drawn organic photovoltaics

Over the past three decades, organic LEDs have gone from promising prototypes to commercial digital displays and light sources (see Physics Today, November 2008, page 26 , and February 2013, page 10 ). Perhaps it’s little surprise that organic photovoltaics (OPVs) are starting down a similar path. OPVs offer the promise of flexible, large-area, and low-cost solar cells and photodetectors. In the lab, test samples are usually prepared by spin-coating: A small amount of solution containing a mix of organic semiconductors is placed on a substrate, and the substrate is spun rapidly to spread the solution into a thin film. The process wastes much of the material, however, and the range of film thicknesses it can produce is limited. Keisuke Tajima and colleagues at the RIKEN Center for Emergent Matter Science in Japan now report a simple, low-cost, less wasteful alternative: drawing on the substrate with a felt-tip marker containing an OPV solution. The figure shows a glass substrate on which parallel lines have been drawn three times; each pass deposited about 90 nm of material. The resulting films are noticeably nonuniform, especially perpendicular to the lines. Nonetheless, the researchers found that pen-coated OPV devices behaved similarly to or slightly better than spin-coated devices of comparable film thickness. (K. Suzuki et al., AIP Adv. 7, 115002, 2017, doi:10.1063/1.5006352 .)