Suns-V$_\textrm{OC}$ characteristics of high performance kesterite solar cells

TL;DR

This study investigates the Suns-$V_{OC}$ characteristics of high-performance CZTSSe solar cells, revealing multiple limiting mechanisms affecting open circuit voltage at high light intensities and low temperatures.

Contribution

It identifies key V$_{OC}$ limiting factors in CZTSSe cells, including defects, low conductivity, and contact issues, using Suns-$V_{OC}$ measurements under various conditions.

Findings

Suns-$V_{OC}$ curves show bending at high light intensity.

Multiple V$_{OC}$ limiting mechanisms are identified.

Non-ohmic back contact can be detected via monochromatic Suns-$V_{OC}$ measurements.

Abstract

Low open circuit voltage ($V_{OC}$) has been recognized as the number one problem in the current generation of Cu$_{2}$ZnSn(Se,S)$_{4}$ (CZTSSe) solar cells. We report high light intensity and low temperature Suns-$V_{OC}$ measurement in high performance CZTSSe devices. The Suns-$V_{OC}$ curves exhibit bending at high light intensity, which points to several prospective $V_{OC}$ limiting mechanisms that could impact the $V_{OC}$, even at 1 sun for lower performing samples. These V$_{OC}$ limiting mechanisms include low bulk conductivity (because of low hole density or low mobility), bulk or interface defects including tail states, and a non-ohmic back contact for low carrier density CZTSSe. The non-ohmic back contact problem can be detected by Suns-$V_{OC}$ measurements with different monochromatic illumination. These limiting factors may also contribute to an artificially lower $J_{SC}$-$V_{OC}$ diode ideality factor.