Gradient bandgap enables >13% efficiency sulfide Kesterite solar cells with open-circuit voltage over 800 mV

TL;DR

This study introduces a novel pre-crystallization method to create a Cd-gradient in CZTS solar cells, significantly enhancing efficiency and open-circuit voltage, marking a major advancement in sulfide Kesterite photovoltaics.

Contribution

The paper presents a new pre-crystallization strategy to control Cd-gradient distribution in CZTS, achieving over 13% efficiency and >800 mV open-circuit voltage in sulfide Kesterite solar cells.

Findings

Achieved 13.5% total-area efficiency in CZTS solar cells.

Realized open-circuit voltage over 800 mV.

Enhanced minority carrier transport and interface properties.

Abstract

Sulfide Kesterite Cu2ZnSnS4 (CZTS), a nontoxic and low-cost photovoltaic material, has always being facing severe charge recombination and poor carrier transport, resulting in the cell efficiency record stagnating around 11% for years. Gradient bandgap is a promising approach to relieve these issues, however, has not been effectively realized in Kesterite solar cells due to the challenges in controlling the gradient distribution of alloying elements at high temperatures. Herein, targeting at the Cd alloyed CZTS, we propose a pre-crystallization strategy to reduce the intense vertical mass transport and Cd rapid diffusion in the film growth process, thereby realizing front Cd-gradient CZTS absorber. The Cd-gradient CZTS absorber, exhibiting downward bending conduction band structure, has significantly enhanced the minority carrier transport and additionally improved band alignment and interface property of CZTS/CdS heterojunction. Ultimately, we have achieved a champion total-area efficiency of 13.5% (active-area efficiency: 14.1%) in the cell and in particular a high open-circuit voltage of >800 mV. We have also achieved a certified total-area cell efficiency of 13.16%, realizing a substantial step forward for the pure sulfide Kesterite solar cell.