Investigating and Understanding S-shape Curves in PEDOT:PSS Based Silicon Heterojunction Solar Cells

Heterojunction silicon solar cells with poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) were fabricated and the formation of S-shape curves was investigated. The S-shape curves are synonymous to degradation observed in these cells. The cells degrade over the period of several weeks, and through a series of electrical and spectroscopic measurements, the source of the S-shape curves and degradation was narrowed to two possible sources: 1.) the junction between the PEDOT:PSS and the Si substrate, or 2.) the electrical conductivity of the PEDOT:PSS. The composition, defects of the SiO
₂
and any electrical present at the interface between the crystalline silicon substrate and the PEDOT:PSS was studied using laboratory Xray photoelectron spectroscopy (XPS), destructively, and synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES), non-destructively.