  Materials with low work functions are critical for an array of applications
requiring the facile removal or efficient transport of electrons through a
device. Perovskite oxides are a promising class of materials for finding low
work functions, and here we target applications in thermionic and field
electron emission. Perovskites have highly malleable compositions which enable
tunable work function values over a wide range, robust stability at high
temperatures, and high electronic conductivities. In this work, we screened
over 2900 perovskite oxides in search of stable, conductive, low-work-function
materials using Density Functional Theory (DFT) methods. Our work provides
insight into the materials chemistry governing the work function value of a
perovskite, where materials with barely filled d bands possess the lowest work
functions. Our screening has resulted in a total of seven promising compounds,
such as BaMoO3 and SrNb0.75Co0.25O3 with work functions of 1.1 eV and 1.5 eV,
respectively. These promising materials and others presented in this study may
find use as low work function electron emitters in high power vacuum electronic
and thermionic energy conversion devices. Moreover, the database of calculated
work functions and materials chemistry trends governing the value of the work
function may aid in the engineering of perovskite heterojunction devices.
