Kelvin force microscopy studies of work function of transparent conducting ZnO:Al electrodes synthesized under varying oxygen pressures

TitleKelvin force microscopy studies of work function of transparent conducting ZnO:Al electrodes synthesized under varying oxygen pressures
Publication TypeJournal Article
Year of Publication2011
AuthorsJaramillo, R, Ramanathan, S
JournalSolar Energy Materials and Solar Cells
Volume95
Issue2
Pagination602 - 605
Date Published2011/02//
ISBN Number0927-0248
KeywordsAtomic Force Microscopy, Kelvin Probe, Oxides, Scanning Probe Microscopy, Thin Films, Transparent Conducting Oxides, Work Function, ZnO
Abstract

The ability to controllably tune the work function of transparent conductors is essential for optimizing the efficiency of thin film solar photovoltaics. Here we use Kelvin force microscopy on lithographically patterned ZnO:Al thin films to measure the dependence of the work function on oxygen content during synthesis. Films were synthesized by low temperature reactive sputtering from a Zn:Al 1.2 wt% target. At optimal oxygen content the resistivity is 3×10-4 [Omega] cm with nearly 90% optical transmission in the 400-1100 nm wavelength range relevant to solar photovoltaics. We find that the expected relationship between band filling and work function breaks down in the vicinity of optimal oxygen stoichiometry. For oxygen-rich ZnO:Al films we measure large work functions close to 5 eV. Our results suggest a method for fabricating transparent oxide electron conductors with large, tunable work functions that could be of relevance in designing electrodes for solid state energy conversion technologies.

URLhttp://www.sciencedirect.com/science/article/B6V51-516KF4F-1/2/1f9af98f20241490ac613d6634124af8