Organic p-n heterojunctions are widely utilized in exciton dissociation and charge-generation layers in optoelectronic devices. In these applications, the energy difference between the highest occupied molecular orbital (HOMO) of a p-type organic semiconductor and the lowest unoccupied molecular orbital (LUMO) of an n-type organic semiconductor (HOMO_p−LUMO_n) significantly affects device performance. Therefore, determining the energy-level alignment of an organic p-n junction is important. In this study, the energy-level alignment of indium tin oxide/pentacene/C₆₀ interfaces was investigated using in-situ ultraviolet and X-ray photoelectron spectroscopy measurements. Type II alignment and significant band bending were observed at the pentacene/C₆₀ interface. The HOMO_p−LUMO_n was measured to be 0.97 eV, similar to reported values. The HOMO_p−LUMO_n was not significantly affected by the substrate work function when the pentacene layer thickness was sufficient. These results are important for the design of efficient organic device architectures.

Keywords: Organic p-n junction, Energy level alignment, Ultraviolet photoelectron spectroscopy, Pentacene, C₆₀