Phosphine Oxide Derivative as a Passivating Agent to Enhance the Performance of Perovskite Solar Cells

Abstract

Defects of metal-halide perovskites detrimentally influence the optoelectronic properties of the thin film and, ultimately, the photovoltaic performance of perovskite solar cells (PSCs). Especially, defect-mediated nonradiative recombination that occurs at the perovskite interface significantly limits the power conversion efficiency (PCE) of PSCs. In this regard, interfacial engineering or surface treatment of perovskites has become a viable strategy for reducing the density of surface defects, thereby improving the PCE of PSCs. Here, an organic molecule, tris(5-((tetrahydro-2H-pyran-2yl)oxy)pentyl)phosphine oxide (THPPO), is synthesized and introduced as a defect passivation agent in PSCs. The PO terminal group of THPPO, a Lewis base, can passivate perovskite surface defects such as undercoordinated Pb2+. Consequently, improvement of PCEs from 19.87 to 20.70% and from 5.84 to 13.31% are achieved in n−i−p PSCs and hole-transporting layer (HTL)-free PSCs, respectively.

Lewis Base Plays a Double-Edged-Sword Role in Trap State Engineering of Perovskite Polycrystals

“…38 The expedited crystallization gives rise to the rapid formation of perovskites within a short time, which is suggested to produce polycrystals with large grain sizes and reduced grain boundaries (Figures S1 and S2). 38 Combined with the well-established surface passivation by Lewis base, 39 it lends confidence that the surface defect states can be effectively diminished via the TU treatment. Nevertheless, it is also reported that swift crystallization is sometimes undesirable for the self-passivation of trap states, which results in more structural defects.…”

Enhanced Thermal Stability of Planar Perovskite Solar Cells Through Triphenylphosphine Interface Passivation

“…Since metallic Pb 0 species in perovskites could act as detrimental non-radiative recombination sites, the addition of TPP molecules could enhance the photovoltaic performance and stability of the PSCs by passivating the undercoordinated Pb 2 + defects and reducing the number of metallic lead species. [42,43] In contrast, the Pb 0 peak is significantly suppressed in the TPP-passivated perovskite film. Figure 1c represents the P 2p 3/2 and P 2p 1/2 peaks corresponding to binding energies of 132.68 and 133.60 eV.…”

“…It is important to note that the pristine perovskite film reveals the presence of metallic lead (Pb 0 ) peaks at binding energies of 136.80 and 141.60 eV, which could be attributed to the chemical reaction between organic components and the adsorbed oxygen/moisture. Since metallic Pb 0 species in perovskites could act as detrimental non‐radiative recombination sites, the addition of TPP molecules could enhance the photovoltaic performance and stability of the PSCs by passivating the undercoordinated Pb 2+ defects and reducing the number of metallic lead species [42,43] . In contrast, the Pb 0 peak is significantly suppressed in the TPP‐passivated perovskite film.…”

Enhancing operational stability in perovskite solar cells by solvent-free encapsulation method

“…One extended approach followed by many groups has succeeded in utilizing the interface engineering strategy to minimize the inuence of moisture and improve stability. [22][23][24][25] For that, many interfacial materials have been investigated, including metal oxides, 26 polymers, 27 and carbon-based materials. 28 As an example of this approach, the use of phenethylammonium iodide (PEAI) as a passivating agent, reduces the trap density (1.53 Â 10 15 cm À3 ) compared to the control sample (2.78 Â 10 15 cm À3 ).…”