Interfaces between metal oxides and organic semiconductor molecules are crucial to the efficient operation of next-generation optoelectronic devices, including organic photovoltaics, field effect transistors, and light-emitting diodes. The electronic interactions at such interfaces are complex and not well understood, preventing rational design of such devices from fundamental principles. Significantly, the electronic properties of metal oxide surfaces can vary enormously with different preparation methods, yielding fundamentally different band alignment and carrier dynamics.To address this problem, we have undertaken a unified spectroscopic study of the prototypical interface between ZnO and C60-. By combining classic interface spectroscopies of ultraviolet photoemission (UPS) and inverse photoemission (IPES) with the cutting-edge abilities of two-photon photoemission (TPPE) and resonant photoemission spectroscopy (RPES), we provide unprecedented insight into the charge carrier physics at the hybrid organic/metal oxide interface. With UPS and IPES, we probe the interfacial energy level alignment. Using TPPE for the first time on a complex interface such as that of thin film ZnO and C60, we spectroscopically monitor defects within the ZnO bandgap. Finally, we also report the first application of the RPES core-hole clock method to charge carrier physics in a metal oxide near an organic semiconductor interface.We apply this unified spectroscopic survey to highly conductive thin-film ZnO samples with differing surface treatments, studying their effect on the interfacial electronic structure. We demonstrate that small but significant shifts in the properties of the ZnO film result in dramatic changes in the interfacial electronic interactions with C60. Drawing on the full range of photoelectron spectroscopies, we derive an atomistic picture of the electronic interactions at the hybrid organic/metal oxide interface. This model provides detailed insight into the carrier physics near ZnO interfaces, and also yields an understanding of the fundamental physical principles of semiconductor interfaces, expected to be broadly applicable.

Unified photoemission spectroscopic picture of defect-driven charge carrier physics at an organic semiconductor/metal oxide interface

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.