Polymer Solar Cells with Micrometer-Scale Engraved Active Nanolayers Fabricated by Pressing with Metal Molds

A micro-engraved bulk heterojunction (BHJ) nanolayer, which is formed by pressing with a micrometer-scale embossed metal mold, was introduced to fabricate polymer:fullerene solar cells. The embossed metal molds with three different pattern sizes were fabricated by employing a typical lithography/etching process. After the embossed metal molds were pressed onto the BHJ layers, which are made with blends of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM), the size of the resulting engraved patterns in the BHJ layers became smaller than that of the embossed patterns in the metal molds. All devices with the engraved patterns showed remarkably enhanced short-circuit current densities and power conversion efficiencies, which were pronounced even at a low mold temperature of 60°C. The enhanced performance has been attributed mainly to the formation of highly-ordered crystalline nanostructures that are localized within the pressed regions in the BHJ layers. This engraving technology can contribute to the speedy roll-to-roll processing of solar cells by shortening thermal treatment steps.