Analytical study of hybrid PEDOT:PSS/Si/PFN heterojunction interfaces for doping-free applications

In this work, we study doping-free hybrid heterojunction interfaces based on silicon, poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS) and conjugated polyelectrolyte poly [(9,9-bis(3′-(N, N-dimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9–dioctylfluorene) (PFN). For this, three types of hybrid structures were fabricated: a single hybrid structure (ITO/PEDOT:PSS/Si–C:H (buffer)/(i) a-Si:H/(n) a-Si:H/Ag), a double hybrid structure (ITO/PEDOT:PSS/Si–C:H (buffer)/(i) a-Si:H/PFN/Al) and an inorganic a-Si:H-based structure reference. The compositional and interface characteristics were studied by secondary ion mass spectroscopy and atomic force microscopy demonstrating a good definition of the PFN and PEDOT:PSS polymer layers through the hybrid structures. However, the PEDOT:PSS/ITO interfaces show degradation with the diffusion of Sn and In into the polymer layer. Finally, to characterize the optical and electrical properties of the heterojunctions, the photovoltaic response of the structures was measured and compared with optical simulations. Good agreement between experimental and simulation results demonstrated the reliability of the deposition process of the organic layers and validates the optical model to describe and optimize the hybrid heterojunctions.