Metal oxide charge transport layers are widely used to promote the interfacial charge transport of organic optoelectronics. Nevertheless, frequently used wide-bandgap metal oxides with low electrical conductivities reveal inherent limitations in the charge transport enhancement. We present the remarkable electro-conductivity enhancement of solution processable ZnO charge transport layers upon dispersing a tiny amount (less than 0.1 wt%) of chemically doped CNTs and the corresponding device performance improvement of light-emitting diodes (OLEDs). Using various undoped or doped CNTs, whose work function was systematically tuned by substitutional doping of electron deficient B or electron rich N,N-doped CNT (N-CNT), the composite showed a lowered work function matching well with the conduction band of ZnO. Consequently, the ZnO/N-CNT nanocomposite transport layer with 0.08 wt% N-CNT showed a five-fold enhancement of electron mobility, while maintaining the intrinsic bandgap energy levels, optical transparency and solution processability of pure ZnO. The inverted OLEDs employing ZnO/N-CNT nanocomposite electron transport layers could facilitate well-balanced electron-hole injection and, thus, more than two-fold enhancement of maximum luminance (from 21 000 cd m(-2) at 14.6 V to 46 100 cd m(-2) at 14.0 V) and efficiency (from 6.9 cd A(-1) at 13.4 V to 14.3 cd A(-1) at 13.6 V). This highly effective charge mobility enhancement enabled by work function tunable, chemically doped CNTs would be beneficial for various organic and inorganic charge transport materials with different energy levels.