Role of oxide at interface between organic layer and silicon substrate in hybrid solar cells

Abstract

Degradation in PEDOT:PSS-silicon hybrid heterojunction solar cells is centered at the organic–silicon interface characterized by an s-shaped JV curve. The effects of interfacial silicon oxide and the degradation of PEDOT:PSS films on solar cell performance were simulated and fit to experimental results and found to be good predictors of JV performance and the development of s-shapes. Transmission line measurement (TLM) studies showed the Ag-PEDOT:PSS interface remains ohmic over 5 weeks and has a contact resistivity < 0.1ohm cm2 over 10 days. X-ray photoelectron spectroscopy (XPS) showed that the interfacial silicon oxide develops rapidly after fabrication with high amounts of suboxide defects that grows and chemically saturates to the native oxide thickness (1.5 nm) and composition as the devices age. Hard X-ray photoelectron spectroscopy (HAXPES) was used to investigate the buried organic–silicon interface and showed that doping in the PEDOT:PSS backbone decreases and the PEDOT:PSS-silicon band alignment does not change measurably as the devices age.