Ultra-Low Work-Function Ytterbium Oxide Contact For Dopant-Free Si Heterojunction Solar Cells

Dopant-free solar cells provide asymmetrical photocarrier transport via application of dissimilar work-function contact materials. Effective engineering of carrier selective work-function (WF) contacts have been studied at length in pursuit of high-performance heterojunction solar cells. However, much of the focus has been on high WF oxides for n-type semiconductors, while low WF metal oxides have received less attention especially in regard to junctions on p-type semiconductors. Herein, we present an ultra-low WF metal oxide, ytterbium oxide (YbOx), as a potential passivating heterojunction contact on p-silicon for solar cell applications. YbOx is processed using an industry-compatible physical vapor deposition method that entails evaporation of metallic Yb followed by self-oxidization within the vacuum chamber. The device is fabricated on 1.5 μm thick p-SOI. The heterojunction exhibits excellent light-to-current conversion properties: picoampere level dark current, high rectification ratio of up to107, and 104 light-to-dark ratio under laser illumination. A surface-gated 3-terminal device is configured to investigate photocarrier recombination and extraction with YbOx contacts, demonstrating its potential for Si heterojunction solar cells.