Breaking the 800 mV open-circuit voltage barrier in antimony sulfide photovoltaics

TL;DR

This study demonstrates that by reducing defect densities in Sb2S3 thin films through controlled growth, it is possible to surpass the previously assumed voltage limit of 800 mV and achieve record open-circuit voltages in Sb2S3 photovoltaics.

Contribution

The paper introduces a defect engineering approach via citrate ligand additives in chemical bath deposition to surpass the 800 mV Voc barrier in Sb2S3 solar cells.

Findings

Achieved a Voc of 824 mV in Sb2S3 solar cells.

Identified S vacancies and Sb on S anti-sites as deep traps.

Reduced grain boundary density improves device performance.

Abstract

Sb2S3 is a promising material for low-toxicity, high-stability next-generation photovoltaics. Despite high optical limits in efficiency, progress in improving its device performance has been limited by severe voltage losses. Recent spectroscopic investigations suggest that self-trapping occurs in Sb2S3, limiting the open-circuit voltage (Voc) to a maximum of approximately 800 mV, which is the level the field has asymptotically approached. In this work, we surpass this voltage barrier through reductions in the defect density in Sb2S3 thin films by modulating the growth mechanism in chemical bath deposition using citrate ligand additives. Deep level transient spectroscopy identifies two deep traps 0.4-0.7 eV above the valence band maximum, and, through first-principles calculations, we identify these to likely be S vacancies, or Sb on S anti-sites. The concentrations of these traps are lowered by decreasing the grain boundary density from 1114+/-52 nm/um2 to 585+/-10 nm/um2, and we achieve a Voc of 824 mV, the record for Sb2S3 solar cells. This work addresses the debate in the field around whether Sb2S3 is limited by defects or self-trapping, showing that it is possible to improve the performance towards the radiative limit through careful defect engineering.