Interface engineering for the improved injection properties of all-solution-processed n-type organic field-effect transistors (OFETs) arising from the use of an inkjet-printed ZnO electron injection layer were demonstrated. The characteristics of ZnO in terms of electron injection and transport were investigated, and then we employed ZnO as the electron injection layer via inkjet-printing during the fabrication of all-solution-processed, n-type OFETs. With the inkjet-printed ZnO electron injection layer, the devices exhibited approximately five-fold increased mobility (0.0058 cm(2)/V s to 0.030 cm(2)/V s), more than twofold increased charge concentration (2.76 x 10(11) cm(-2) to 6.86 x 10(11) cm(-2)), and two orders of magnitude reduced device resistance (120 M Omega cm to 3 M Omega cm). Moreover, n-type polymer form smoother film with ZnO implying denser packing of polymer, which results in higher mobility. (C) 2017 Elsevier B.V. All rights reserved.