Electron-selective quinhydrone passivated back contact for high-efficiency silicon/organic heterojunction solar cells

Abstract Interfacial properties play a critical role in the dynamic process of carrier transport in dopant-free silicon (Si) heterojunction solar cells (HSCs), based on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). In this study, we use quinhydrone (QHY) to engineer the interfacial properties by grafting the semiquinone (QH) on Si surface at low temperature. The QH monolayer provides effective chemical and field-effect passivation by the surface dangling-bond saturation and its interface dipole, respectively, and results in a large minority carrier lifetime of 477 μs. At the front Si/PEDOT:PSS interface, the QH-terminated Si surface presents higher wettability for the improved contact at the Si/PEDOT:PSS junction. At the rear Al/Si interface, the work function of Al film is reduced significantly to form ohmic contact for electron-selective transport. The dark current-voltage and capacitance-voltage measurements show the improved electric characteristics with a higher carrier collection efficiency. Furthermore, the silicon band bending generated by the QH dipoles enhances the overall built-in potential of Si/PEDOT:PSS HSCs for a larger open-circuit voltage. As a result, the QHY modified Si/PEDOT:PSS HSC yields a power conversion efficiency of 13.29%. This approach demonstrates that the organic grafting is a simple, effective and low-cost method for the interface engineering to achieve high-efficiency HSCs.