Ferroelectric BaTiO3 Nanoparticles Embedded at the p-n Heterojunction Interface Improves the Carrier Transport in Kesterite Solar Cells

The built-in field (E-bi) is a key factor for the dynamic of carrier transport in the heterojunction interface, thus determining the photovoltaic performance of the solar cell, such as Cu2ZnSn(S,Se)(4) (CZTSSe) cell. It is critical to improve the carriers' transport across the pn heterojunction for the fabrication of highly efficient solar cells. In this work, the large electric field of ferroelectric BaTiO3 nanoparticles (BTO NPs) is used to tailor the carrier transport in the CZTSSe solar cells by embedding BTO NPs into the interface of CZTSSe/CdS heterojunction. It is very surprising that a polarization electric field (E-P) with the same direction of E-bi synergically enhances carrier transport greatly and increases the PCE by 20.6%. Further study on the mechanism discloses that BTO NPs reduce the work function of CZTSSe and CdS and form interfacial dipoles at their interface, which is conducive to the photogenerated electrons to be collected by the electron transport layer. This strategy also works well on other thin film solar cells and gives a new aspect of strengthening the carrier transport between p-n heterojunction.