Impact of metastable defect structures on carrier recombination in solar cells

TL;DR

This paper investigates how metastable defect structures, especially in materials like CdTe, influence carrier recombination in solar cells, revealing new pathways that could impact efficiency limits.

Contribution

It introduces the role of metastable defect configurations in carrier capture processes, expanding beyond static trap models in photovoltaic materials.

Findings

Metastable defect structures can significantly alter recombination pathways.

Symmetry-breaking in defects activates new carrier capture mechanisms.

Metastable defects are particularly relevant in complex, ionic-covalent semiconductors.

Abstract

The efficiency of a solar cell is often limited by electron-hole recombination mediated by defect states within the band gap of the photovoltaic (PV) semiconductor. The Shockley-Read-Hall (SRH) model considers a static trap that can successively capture electrons and holes. In reality however, true trap levels vary with both the defect charge state and local structure. Here we consider the role of metastable structural configurations in capturing electrons and holes, taking the tellurium interstitial in CdTe as an illustrative example. Consideration of the defect dynamics, and symmetry-breaking, changes the qualitative behaviour and activates new pathways for carrier capture. Our results reveal the potential importance of metastable defect structures in non-radiative recombination, in particular for semiconductors with anharmonic/ionic-covalent bonding, multinary compositions, low crystal symmetries or highly-mobile defects.