Enhanced performance of ZnO based perovskite solar cells by Nb2O5 surface passivation

Abstract

Abstract TiO2 has been extensively utilized as bottom electron transporting scaffold for perovskite solar cells (PSCs) but need for its high processing temperature (>450 °C) hinders its applicability for the flexible plastic substrates. Use of the low temperature processed ZnO is one of the probable solutions as electron transport layer (ETL) in PSCs owing to its high electron mobility. An amicable solution for the instability of the perovskite absorber layers fabricated on to ZnO leading resulting in to poor power conversion efficiency (PCE) and long-term stability is necessary for to harness the benefit of ZnO as ETL in PSCs. Herein, we modified the ZnO surface by spin-coating an ultrathin Nb2O5 as surface passivation layer. In this work, both of the ZnO and Nb2O5 were fabricated by spin coating and sintered at relatively lower temperature of 200 °C. Utilizing this Nb2O5 surface passivated and low temperature processed ZnO as ETL, dramatically enhanced stability of perovskite film over 20 days under ambient condition has been clearly demonstrated. This bilayer of Nb2O5 surface passivated ZnO scaffold used for fabrication of the planer heterojunction PSCs based on CH3NH3PbI3, led to the maximum PCE of 14.57% under simulated solar irradiation for an optimized ZnO thickness of 42 nm. Moreover, implication of the surface passivation of ZnO by Nb2O5 leading to the formation of highly crystalline, stable and dense perovskite film has been probed by SEM and XRD investigations.