Piperazine-Assisted Construction of 2D/3D Wide-Bandgap Perovskite for Realizing High-Efficiency Perovskite/Organic Tandem Solar Cells

Abstract

Monolithic perovskite/organic tandem solar cells (TSCs) have gained significant attention due to their easy device integration and the potential to surpass the Shockley–Queisser limit of single-junction solar cells. However, the surfaces of wide-bandgap perovskite films are densely populated with defects, leading to severe non-radiative recombination and energy loss. As a consequence, the power conversion efficiency (PCE) of perovskite/organic TSCs lags behind that of other TSC counterparts. To address these issues, we designed a functional ammonium salt, 4-(2-hydroxyethyl)piperazin-1-ium iodide (PZOI), comprising a piperazine iodide and a terminated hydroxyl group, which was applied for post-treating the perovskite surface. Our findings reveal that PZOI reacts with and consumes residual PbX ₂ (X: I or Br) to form a 2D perovskite component, thereby eliminating Pb ⁰ defects, while the terminated hydroxyl group in PZOI can also passivate uncoordinated Pb ²⁺. Consequently, the shallow/deep-level defect densities of the 2D/3D perovskite film were significantly reduced, leading to an enhanced PCE of single-junction 2D/3D wide-bandgap perovskite solar cells to 18.18% with a reduced energy loss of 40 meV. Importantly, the corresponding perovskite/organic TSCs achieved a remarkable PCE of 24.05% with enhanced operational stability ( T ₉₀ ∼500 h).

Keywords

Perovskite/organic tandem solar cell / Defect states / Piperazine ion salt / Energy conversion / Low-dimensional materials / Perovskite solar cells / 2D/3D perovskites / Efficiency

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2024 SIOC, CAS, Shanghai, & WILEY-VCH GmbH