title: Impact of Sn(S,Se) secondary phases in Cu2ZnSn(S,Se)4 solar cells: a chemical route for their selective removal and absorber surface passivation.
abstract: The control and removal of secondary phases is one of the major challenges for the development of Cu2ZnSn(S,Se)4 (CZTSSe)-based solar cells. Although etching processes have been developed for Cu(S,Se), Zn(S,Se), and CuSn(S,Se) secondary phases, so far very little attention has been given to the role of Sn(S,Se). In this paper, we report a chemical route using a yellow (NH4)2S solution to effectively remove Sn(S,Se). We found that Sn(S,Se) can form on the surface either because of stoichiometric deviation or by condensation. After etching, the efficiency of devices typically increases between 20 and 65% relative to the before etch efficiencies. We achieved a maximum 5.9% efficiency in Se-rich CZTSSe-based devices. It is confirmed that this feature is related not only to the removal of Sn(S,Se) but also to the unexpected passivation of the surface. We propose a phenomenological model for this passivation, which may open new perspectives for the development of CZTSSe-based solar cells.
authors.affiliation: IREC, Catalonia Institute for Energy Research , Jardins de les Dones de Negre 1, 2a, 08930 Sant Adrià del Besòs, Spain.
authors.forename: Haibing
authors.initials: H
authors.lastname: Xie
authors.forename: Yudania
authors.initials: Y
authors.lastname: Sánchez
authors.forename: Simón
authors.initials: S
authors.lastname: López-Marino
authors.forename: Moisés
authors.initials: M
authors.lastname: Espíndola-Rodríguez
authors.forename: Markus
authors.initials: M
authors.lastname: Neuschitzer
authors.forename: Diouldé
authors.initials: D
authors.lastname: Sylla
authors.forename: Andrew
authors.initials: A
authors.lastname: Fairbrother
authors.forename: Victor
authors.initials: V
authors.lastname: Izquierdo-Roca
authors.forename: Alejandro
authors.initials: A
authors.lastname: Pérez-Rodríguez
authors.forename: Edgardo
authors.initials: E
authors.lastname: Saucedo