Tuning the Performance of Ge-Doped CZTSSe Solar Cells via Selenization

Area of Science:

• Materials Science
• Renewable Energy
• Semiconductor Physics

Background:

• Cu2ZnSn(S,Se)4 (CZTSSe) is a promising thin-film photovoltaic material limited by defect-induced nonradiative recombination.
• Low-concentration Germanium (Ge) doping can mitigate these defects, but selenization temperature critically impacts CZTSSe properties.

Purpose of the Study:

• To investigate the effect of selenization temperature on the structural, compositional, and optoelectronic properties of Ge-doped CZTSSe.
• To optimize the selenization process for improved photovoltaic performance in Ge-doped CZTSSe thin-film solar cells.

Main Methods:

• Synthesis of Ge-doped Cu2ZnSn0.95Ge0.05S4 (CZTGS) precursor films via a green solution approach.
• Selenization of precursor films at temperatures ranging from 530 °C to 570 °C.
• Comprehensive characterization using XRD, SEM, XPS, EDS, and AFM.

Main Results:

• Selenization temperature significantly influences film microstructure, crystallinity, elemental composition, and surface roughness.
• The film selenized at 550 °C exhibited optimal crystallinity, grain structure, Ge incorporation, and lowest surface roughness.
• This optimal condition led to reduced carrier transport resistance, improved recombination resistance, inhibited nonradiative recombination, and prolonged carrier lifetime.
• The resulting Cu2ZnSn0.95Ge0.05(S,Se)4 (CZTGSSe) solar cell achieved a power conversion efficiency (PCE) of 8.69%, with V_OC = 0.42 V, FF = 55.51%, and J_SC = 37.71 mA·cm⁻².

Conclusions:

• Selenization temperature is a critical parameter for controlling the properties and performance of Ge-doped CZTGSSe thin-film solar cells.
• The study elucidates the mechanism by which selenization temperature affects Ge-doped kesterite devices.
• Findings provide insights for optimizing processes for cost-effective, high-performance, and environmentally friendly thin-film solar cells.