A novel strategy to control defects and secondary phases of CZTS by surfactant Potassium

TL;DR

This paper investigates how surfactant potassium can control defects and secondary phases in CZTS, a promising photovoltaic material, by altering surface kinetics during growth, leading to improved crystal quality and device performance.

Contribution

It introduces a first-principles approach to understand defect formation in CZTS and proposes potassium as a surfactant to mitigate detrimental defects and secondary phases.

Findings

Potassium surfactant reduces ZnCu defect formation.

Surface kinetic processes are altered by potassium, improving crystal quality.

Experimental observations align with the proposed surfactant strategy.

Abstract

Cu2ZnSnS4 (CZTS) is a promising photovoltaic absorber material with earth abundant and nontoxic elements. However, the detrimental native defects and secondary phases of CSTS will largely reduce the energy conversion efficiencies. To understand the origin of these problems during the growth of CZTS, we investigated the kinetic processes on CZTS (-1-1-2) surface, using first principles calculations. A surface Zn atom was found to occupy the subsurface Cu site easily due to a low reaction barrier, which may lead to a high ZnCu concentration and a secondary phase of ZnS. These n-type defects may create deep electron traps near the interface and become detrimental to device performance. To reduce the population of ZnCu and the secondary phase, we propose to use K as a surfactant to alter surface kinetic processes. Improvements on crystal quality and device performance based on this surfactant are consistent with early experimental observations.