Fingerprint of Charge Redistribution in the Optical Spectra of Hybrid Inorganic/Organic Semiconductor Interfaces

Hybrid structures combining conjugated organic molecules and inorganic semiconductors hold the promise to merge the better of two worlds. To achieve optoelectronic functionality exceeding that of the individual constituent, both the electronic and the optical properties of the hybrid interface must meet certain requirements. Charge redistribution occurring upon deposition of conjugated organic molecules on semiconductor surfaces modulates the electrostatic potential at the hybrid interface. Here we show at the example of ZnO-based hybrid systems that even minuscule charge redistribution is accompanied by a profound modification of the excitonic absorption of the semiconductor. The changes in the optical spectra are detected in real time by differential reflectance spectroscopy (DRS) during the deposition of the molecules. Appropriate modeling of the spectra yields the magnitude of the change of the electrostatic potential. Our findings provide insight into the subtle interplay between optical and electronic properties at hybrid interfaces which is essential to design structures with truly superior function