Charge transfer highways in polymer solar cells embedded with imprinted PEDOT:PSS gratings

This study presents the developed poly(3-hexylthiophene):indene-C₆₀ bisadduct (P3HT:ICBA)-based organic solar cells, where nanoimprinted poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) gratings successfully functioned as charge transport highways and induced an ICBA-rich surface. The embedded nanostructures improved light harvesting and contact area; however, these two factors were not the primary enhancers of solar cell performance. Atomic force microscopy and conductive atomic force microscopy revealed that the imprinted PEDOT:PSS gratings activated hole- and electron-conducting pathways. This result can be attributed to the enhancement of the π-π orbital overlap between P3HT and PEDOT:PSS polymer chains and to the grating-induced ICBA phase separation. These two effects were the primary factors that increased the short-circuit current of the imprinted devices, which resulted in the increase of power conversion efficiency. In-plane and out-of-plane grazing incident X-ray diffraction revealed that the chain orientation of P3HT on the PEDOT:PSS gratings was the same as that on the plane PEDOT:PSS surface. This study proved the feasibility of nanoimprinting for organic solar cells, as well as for organic field-effect transistors.