Thin film electronic and optoelectronic devices demand electrodes with a work function (Φ) that is sufficiently low to facilitate the transport of electrons in and out of the lowest unoccupied molecular orbital of a given semiconductor. Herein, phenothiazine‐, carbazole‐, and fluorene‐based phenylquinoline derivatives as efficient interfacial layer (IL) materials for solution‐processable organic and metal oxide electronic devices are reported. The IL is applied on top of a charge injection electrode in various solution‐processed devices, including n‐channel organic thin‐film transistors (OTFTs) with [6,6]‐phenyl C71‐butyric acid methyl ester (PC71BM) and poly[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4:5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene) [P(NDI2OD‐T2)] and amorphous indium gallium zinc oxide (IGZO) transistors, and also in organic photovoltaics (OPVs). Both PC71BM‐ and P(NDI2OD‐T2)‐based n‐channel OTFTs with IL show enhanced mobility by more than 200% compared to bare Au electrode. IGZO transistors showed much improved mobility of 15.3 cm2 V−1 s−1 with an IL compared to bare Au (0.6 cm2 V−1 s−1 ) device. A significantly improved power conversion efficiency (PCE) of 7.63% is obtained for IL utilizing the poly[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]‐thiophenediyl] (PTB7):PC71BM based OPVs compared to 4.75% of control device. Ultraviolet photoelectron spectroscopy study reveals that phenylquinoline derivatives significantly lower the Φ of Au, thus facilitating electron injection/extraction in the device.