Here, for the first time, the high-yield (87.6%) robust and facile synthesis of water-processable donor–acceptor Janus nanoparticles (JNP) that are of high potential for optoelectronic applications is reported. The water-processable JNPs have easily controlled Janus ratios and are of excellent quality, which is shown by energy-filtered transmission electron microscopy. The JNPs exhibit improved charge separation and transfer properties compared to the conventional donor–acceptor nanoparticles which is characterized via both steady-state and transient photoluminescence spectroscopy. The Janus character of particles allows the combination of two materials into one composite and programs morphology of structures, which can be formed on the basis of the particles. Finally, outstanding performance of JNP-based photovoltaic cells with 53% improvement of efficiency is shown.