Interfacial Passivation Using 2D Perovskite for an Efficient and Stable Wide-Bandgap Perovskite Solar Cells

The three-dimensional/two-dimensional (3D/2D) heterostructure recently emerged as a fascinating approach for making efficient, scalable, and stable perovskite solar cells (PSCs). The 2D capping layer is crucial in perovskite/ electron transport layer (ETL) interfacial passivation and in inhibiting environmental stress [1,2,3].<br/>In this work, we demonstrate a novel solution process to tailor the dimensionality (n) of the 2D perovskite at the 3D perovskite/ETL interface of <i>p-i-n</i> device architecture by tuning the molar concentration of 2D perovskite precursor. We optimized the molarity of 2D precursor by varying its concentration and found that 10 mM is the optimum concentration on top of wide bandgap (WBG) 3D perovskite layer (FA_0.83Cs_0.17Pb(I_0.8Br_0.2)₃, 1.67 eV). However, further increase in concentrations (&gt; 10 mM) led to the formation of mixed phases (n=2, 3, 4) of 2D perovskite as confirmed by X-ray diffraction (XRD) and steady-state photoluminescence (SSPL) measurements. Furthermore, transient photovoltage/photocurrent and fluorescence decay experiments reveal that an optimized 3D/2D heterostructure enables efficient passivation of perovskite surface defects, prolongs carrier lifetime, retard non-radiative interfacial recombination, and forms better energy level matching with ETL.<br/>The optimized 2D modified wide-bandgap PSCs demonstrate an average power conversion efficiency (PCE) of ~20.75% (0.175 cm²) and ~18.43 % (0.805 cm²) and an open-circuit voltage (<i>V_oc</i>) of ~1.21 V in a <i>p-i-n</i> architecture. Furthermore, the unencapsulated devices exhibit excellent air (RH ~ 55-60%) and heat (85°C) stability by retaining 98% and 82% of their initial efficiency after 800 hours respectively.<br/><br/><br/>References:<br/>1. Yang, G. et al. Stable and low-photovoltage-loss perovskite solar cells by multifunctional passivation. Nat. Photon. 15, 681–689 (2021).<br/>2. Azmi, R. et al. Damp heat-stable perovskite solar cells with tailored-dimensionality 2D/3D heterojunctions. Science 376, 73–77 (2022).<br/>3. Ye et al. Expanding the low-dimensional interface engineering toolbox for efficient perovskite solar cells. Nature Energy 8, 284-293 (2023).