Electric and Photoelectric Properties of 3,4-Ethylenedioxythiophene-Functionalized n-Si/PEDOT:PSS Junctions.

Organic/inorganic solid-state junctions play a critical role in tandem artificial photosynthetic devices supported by conducting polymer membranes. Recent work with n-Si/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) hybrid junctions has shown that the electrical behavior is dominated by the passivating groups present on the silicon surface. In this work, the photovoltaic behavior of n-Si/ PEDOT: PSS was investigated with methyl, thiophene, and 3,4-ethylenedioxythiophene (EDOT) groups covalently attached to the Si(111) surface. X-ray photoelectron spectroscopy results demonstrated that complete monolayer coverage was achieved in 3 h and that the organic passivating groups were retained over two months of exposure to ambient conditions with minimal silicon oxidation. All surfaces investigated exhibited similar light-limited photocurrents and bulk-limited open-circuit voltages, and thiophene produced a dramatic reduction of the fill factor attributed to the formation of trap states at the interface. Furthermore, shunt behavior observed near the power-producing regions for the thiophene and EDOT surfaces is indicative of increased recombination events under forward bias and suggests that hole transport across the interface is enhanced. Thus, thiophene- and EDOT-functionalized Si(111) offer similar stabilities and efficiencies to those of methylated surfaces as well as enhanced hole transport to the PEDOT: PSS interface from the n-Si surfaces.