A Polymer/Carbon-Nanotube Ink as a Boron-Dopant/Inorganic-Passivation Free Carrier Selective Contact for Silicon Solar Cells with over 21% Efficiency

Traditional silicon solar cells extract holes and achieve interface passivation with the use of a boron dopant and dielectric thin films such as silicon oxide or hydrogenated amorphous silicon. Without these two key components, few technologies have realized power conversion efficiencies above 20%. Here, a carbon nanotube ink is spin coated directly onto a silicon wafer to serve simultaneously as a hole extraction layer, but also to passivate interfacial defects. This enables a low-cost fabrication process that is absent of vacuum equipment and high-temperatures. Power conversion efficiencies of 21.4% on an device area of 4.8 cm(2)and 20% on an industrial size (245.71 cm(2)) wafer are obtained. Additionally, the high quality of this passivated carrier selective contact affords a fill factor of 82%, which is a record for silicon solar cells with dopant-free contacts. The combination of low-dimensional materials with an organic passivation is a new strategy to high performance photovoltaics.