In Situ Formation of ZnO in Graphene: A Facile Way To Produce a Smooth and Highly Conductive Electron Transport Layer for Polymer Solar Cells

A novel electron transport layer (ETL) based on zinc oxide@graphene:ethyl cellulose (ZnO@G:EC) nanocomposite is prepared by in situ formation of zinc oxide (ZnO) nanocrystals in a graphene matrix to improve the performance of polymer solar cells. Liquid ultrasound exfoliation by ethyl cellulose as stabilizer not only :allows for uniform dispersion of graphene solution but also maintains an original structure of graphene,gaining a high conductivity. The ZnO@G:EC ETL displays a quite smooth morphology and develops the energy-level alignment for the electron extraction and transportation. Subsequently, the device based on poly(3-hexylthiophene) (P3HT):(6,6)-phenyl-C-61 butyric acid methyl ester (PC61BM) with the ZnO@G:EC as ETL obtains a power conversion efficiency (PCE) of 3.9%, exhibiting a similar to 20% improvement compared to the familiar device with bare ZnO nanocrystals as ETL. Replacing the active layer with polythieno[3,4-b]thiophene/benzodithiophene (PTB7): (6,6)-phenyl-C-71 butyric acid methyl ester (PC71BM,), the PCE can be dramatically improved to 8.4%. This facile and fascinating method to produce a smooth and highly conductive electron transport layer provides an anticipated approach to obtain high performance polymer solar cells.