Work

A Vapor Pressure‐Mediated Annealing Strategy for Vertically Oriented Trigonal Selenium Films Enabling Efficient Solar Cells

Year: 2026

Type: article

Abstract: ABSTRACT Selenium (Se), as the oldest photovoltaic material, has regained research interest recently due to the wide bandgap, high stability, and non‐toxicity of its trigonal phase ( t ‐Se). However, its device performance is fundamentally limited by the strong anisotropic carrier transport inherent in its typical low‐dimensional crystal orientation, where Se chains lie parallel to the substrate. Herein, we report a vapor pressure‐mediated annealing strategy, namely dubbed dual‐sheath annealing (DSA), to overcome this bottleneck. By recrystallizing amorphous Se films under a precisely controlled high Se vapor pressure, we direct a surface re‐evaporation and re‐deposition process that induces a novel top‐down growth mode. This method successfully fabricates t‐Se films with a dominant vertical [101] orientation, a texture that facilitates efficient longitudinal charge transport. The resulting films feature large, smooth grains, which further enable robust coupling with a 2D MXene hole‐transport layer via Coulomb force. The constructed FTO/TiO 2 /t‐Se/MXene solar cells achieve a champion power conversion efficiency of 6.5%, which surpasses the performance of devices from traditional annealing by 33.74% and outperforms reference devices with Au electrodes by 11.11%. This work establishes vapor pressure control as a powerful and general thermodynamic lever for tailoring crystal orientation in low‐dimensional semiconductor films for high‐performance optoelectronics.

Source: Advanced Functional Materials

DOI: 10.1002/adfm.74418