Charge Carrier Transport Mechanism through Different Oxides for (n) Poly‐Si/Siox Fired Passivating Contacts

Abstract

In recent years the mechanism of carrier transport through a junction of polycrystalline silicon (poly‐Si) on an interface oxide has been extensively discussed for passivating contacts of crystalline silicon‐based solar cells fabricated along the well‐established high temperature route. In the fired passivating contact (FPC) approach, no extended crystallization is foreseen which also modifies the properties of the junction. Herein, investigation of atmospheric pressure chemical vapor deposited (APCVD), phosphorus‐doped (n) poly‐Si is done, which is annealed at different temperatures and durations following the FPC approach. Symmetric lifetime samples show the passivation potential of the FPC approach with implied open circuit voltages (iVOC) values of up to 736 mV. Temperature‐dependent specific contact resistivity measurements applying the transfer length method on differently grown interface oxides are used to identify tunneling or pinhole transport, or a combination of both. It is found that a transition from tunneling to pinhole transport surprisingly takes place already for annealing durations of a few seconds and is primarily impacted by annealing temperature instead of duration. Pinhole magnification studies via tetramethylammonium etching and scanning electron microscopy (SEM) confirm the existence of pinholes in the interfacial oxides.