Improving Polymer Tandem Solar Cells

Blending gold nanoparticles into the layer connecting the two subcells of a polymer tandem solar cell boosts the device’s performance, according to researches at UCLA, the Chinese Academy of Sciences, and Japan’s Yamagata University (ACS Nano, DOI: 10.1021/nn202144b). Organic photovoltaic (OPV) cells offer the promise of low-cost power production and flexibility in applications (literally), but the efficiency with which OPV devices convert light to electricity has remained low, at about 7–8% (C&EN, Aug. 23, 2010, page 12). Conversion efficiency improvements of less than 1% make headlines in this field. One strategy to boost that value calls for stacking two light-absorbing materials in a tandem cell to harvest a greater fraction of the solar spectrum. By inserting a nanoparticle layer between two subcells, UCLA’s Yang Yang and coworkers coupled the tandem cell strategy with the plasmonic effect—a process that concentrates light via scattering from nanoparticles. One subcell was made from a conducting polymer/fullerene-derivative blend known as P3HT:ICBA. The other included a diazole polymer/fullerene-derivative combination designated PSBTBT:PC₇₀BM. The conversion efficiency of either cell alone was less than 3.5%. The value for the metal-free tandem cell rose to 5.2%. Adding the nanoparticle layer further raised the efficiency to 6.2%.