Governing the dispersion of quasi-2D perovskite phases toward efficient and stable perovskite solar cells

Multiphase formations within quasi-two-dimensional (quasi-2D) perovskite films have been shown to impede efficient charge transfer, reducing device performance. To address this issue, we propose using acetic acid (AcOH) as an additive to achieve a narrow phase distribution in quasi-2D perovskite films. In situ UV-visible light absorption spectra show an effective reduction in phase polydispersity in the early stage of film crystallization. First-principles calculations confirm that the AcOH coordination alters the reaction path, lowering the enthalpy of formation for a concentrated phase distribution. This configuration leads to carrier diffusion length exceeding 1 μm, and the mobility is up to 7.18 cm² V⁻¹ s⁻¹ in the quasi-2D perovskite film. The resultant solar cells exhibit a champion power conversion efficiency (PCE) of 19.05% and demonstrate exceptional long-term stability, retaining over 90% of their initial PCEs over 10,000 h and maintaining over 80% efficiency after 500 h under continuous illumination tracking at the maximum power point.