Curcumin: A Natural Electron Acceptor for Organic Optoelectronics

Utilizing biorenewable molecules is essential to directing organic electronics toward a circular economy framework, where spent devices are recyclable or decomposable. Natural pigments are potential candidates for photosensitizers and organic semiconductors among numerous bioderived molecules. However, few molecules are known to function as electron acceptors applicable to photoelectric conversion devices, such as organic photovoltaics (OPVs) and photodetectors. This work reports that curcumin, a yellow pigment naturally occurring as turmeric, functions as an acceptor with a high absorption coefficient and favorable energy of the lowest unoccupied molecular orbital (LUMO). External quantum efficiency spectra indicate that an inverted OPV based on a bulk-heterojunction of curcumin and poly(3-hexylthiophene) (P3HT) generates a photocurrent four times higher than that of a P3HT-based Schottky OPV. Although the current density of the P3HT:curcumin OPV is moderate due to the low electron mobility of curcumin, its shallow LUMO provides a high open-circuit voltage of up to 0.78 V. Thorough device optimizations boost the power conversion efficiency to 0.29% even for the OPV comprising a 30 nm-thick photoactive layer. The performance is the highest among OPVs based on naturally occurring acceptors. The study presented here inspires the exploration of natural molecules that can be applied to organic electronics.