Improvement of the SiO_x passivation layer for high-efficiency Si/PEDOT: PSS heterojunction solar cells

Interfacial properties currently hinder the performance of Si/ organic heterojunction solar cells for an alternative to high-efficiency and lowcost photovoltaics. Here, we present a simple and repeatable wet oxidation method for developing the surface passivation layer, SiO_x, on the Si surface for the fabrication of high-efficiency Si/poly(3,4-ethylene-dioxythiophene):polystyrenesulfonate (PEDOT:PSS) heterojunction solar cells. The uniform and dense SiO_x thin layer introduced by the oxidizing aqueous solution of H₂O₂ or HNO₃ provided the better surface passivation and stronger wettability of the Si surface, compared to those in the native oxide case. These two types of progress helped create a lower defect density at the Si/PEDOT:PSS interface and thus a high-quality p-n junction with a lower interface recombination velocity. As a result, the HNO₃-oxidized device displayed better performance with a power conversion efficiency (PCE) of 11%, representing a 28.96% enhancement from the PCE of 8.53% in the native oxide case. The effects on the performance of the Si/PEDOT:PSS hybrid solar cells of the wet oxidation treatment procedure, including the differences in surface roughness and wettability of the Si substrate, the quality and thickness of the SiO_x, etc., were explored extensively. Such a simple and controllable oxidizing treatment could be an effective way to promote the interfacial properties that are an important cornerstone for more efficient Si/organic hybrid solar cells.