This work investigates the energy-level alignment of hybrid inorganic/organic systems (HIOS) comprising ZnO as the major inorganic semiconductor. In addition to offering essential insights, the thesis demonstrates HIOS energy-level alignment tuning within an unprecedented energy range. (Sub)monolayers of organic molecular donors and acceptors are introduced as an interlayer to modify HIOS interface-energy levels. By studying numerous HIOS with varying properties, the author derives generally valid systematic insights into the fundamental processes at work. In addition to molecular pinning...