Japheth Joseph Yeow Wan Foong,† Benny Febriansyah,† Prem Jyoti Singh Rana, Teck Ming Koh, Darrell Jun Jie Tay, Annalisa Bruno, Subodh Mhaisalkar, Nripan Mathews*
A series of all-organic alkylammonium alkanoate salts were developed to both passivate halide perovskite surface or grain boundaries defect sites and enhance the hydrophobic character of the material. Power conversion efficiency (PCE) higher than 18.5% were obtained from the treated samples, representing more than 5% improvement relative to the pristine MAPbI3 devices. The unencapsulated device retains 85% of its initial PCE upon treatment, while the pristine device loses 50% of its original PCE when both are subjected to ambient environment over 1500 h
Abstract:
Surface imperfections created during fabrication process in halide perovskites (HPs) films could induce formation of various defect sites that affect device performance and stability. In this work, all-organic surface modifiers consisting of alkylammonium cations and alkanoate anions are introduced on top of HP layer to passivate the interfacial vacancies and improve moisture tolerance. Endowed with both ammonium and carboxylate groups, the passivators are capable of sitting in the A-site vacancy left by the small organic cation, while concurrently filling in the vacant X-site created due to the halide loss. Passivation using alkylammonium alkanoate was found to not induce formation of any low-dimensional perovskites species. Instead, the organic species only passivate the perovskite’s surface and grain boundaries, which results in enhanced hydrophobic character of the HP films. In terms of photovoltaic application, passivation with alkylammonium alkanoate allows significant reduction in recombination losses and enhancement of open-circuit voltage. Together with unchanged short-circuit current density, power conversion efficiency of more than 18.5 % can be obtained from the treated sample. Furthermore, the unencapsulated device retains 85 % of its initial PCE upon treatment, while the standard 3D perovskite device loses 50% of its original PCE when both are subjected to ambient environment over 1500 hours.
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