# Spectroscopic Signatures of Structural Disorder and Electron‐Phonon Interactions in Trigonal Selenium Thin Films for Solar Energy Harvesting

## TL;DR

This paper shows how controlling the structure of selenium thin films can improve their performance for solar energy applications.

## Contribution

A closed-space encapsulation strategy enables non-destructive probing of selenium thin films to reveal processing effects on structural disorder and optoelectronic quality.

## Key findings

- Short-range structural disorder in selenium thin films is sensitive to processing variations, not intrinsic to the material.
- Structural disorder and stress promote extended defects that limit photovoltaic performance by increasing non-radiative recombination.
- Precise control of synthesis and post-deposition treatments can significantly improve the optoelectronic quality of selenium thin films.

## Abstract

Selenium is experiencing renewed interest as a elemental semiconductor for a range of optoelectronic and energy applications due to its irresistibly simple composition and favorable wide bandgap. However, its high volatility and low radiative efficiency make it challenging to assess structural and optoelectronic quality, calling for advanced, non‐destructive characterization methods. In this work, we employ a closed‐space encapsulation strategy to prevent degradation during measurement and enable sensitive probing of vibrational and optoelectronic properties. Using temperature‐dependent Raman and photoluminescence spectroscopy, we investigate grown‐in stress, vibrational dynamics, and electron‐phonon interactions in selenium thin films synthesized under nominally identical conditions across different laboratories. Our results reveal that short‐range structural disorder is not intrinsic to the material, but highly sensitive to subtle processing variations, which strongly influence electron‐phonon coupling and non‐radiative recombination. We find that such structural disorder and grown‐in stress likely promote the formation of extended defects, which act as dominant non‐radiative recombination centers limiting carrier lifetime and open‐circuit voltage in photovoltaic devices. These findings demonstrate that the optoelectronic quality of selenium thin films can be significantly improved through precise control of synthesis and post‐deposition treatments, outlining a clear pathway toward optimizing selenium‐based thin film technologies through targeted control of crystallization dynamics and microstructural disorder.

Selenium plays hard to get ‐ volatile, low radiative efficiency, and highly sensitive to processing. Using a closed‐space encapsulation strategy, we probe room‐temperature photoluminescence and quantify structural disorder, showing how precise structural control can turn selenium into a high‐performance optoelectronic material of tomorrow.