Atomic scale observation and characterization of redox-induced interfacial layers in commercial Si thin film photovoltaics

Abstract

Thermodynamics considerations and experimental evidence suggest that redox reactions occur at the interfaces between transparent conductive oxides (TCOs) and the active silicon layers in photovoltaic stacks, with potentially nefarious effects to device efficiency. The presence of interfacial layers of oxidized silicon and reduced metal is confirmed here with analytical depth profiling techniques in industrially produced Si thin film solar cells. Atomic-resolution scanning transmission electron microscopy and energy loss spectroscopy are used to show that the specific chemistry of the interface, the front TCO being Sn-rich while the back TCO is Zn-rich, has a strong influence on the size of the resulting interfacial layer. Furthermore, the morphology of the interface and the impact of annealing treatments are also studied, leading to suggestions for possible improvements of commercial device efficiency.