Efficient (Cu_1- Ag )₂ZnSn(S,Se)₄ solar cells on flexible Mo foils

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Cation substitution is key to enhancing copper zinc tin sulfide selenide (CZTSSe) solar cell performance.
• Flexible CZTSSe solar cells on molybdenum foils require efficiency improvements.

Purpose of the Study:

• To investigate the effect of partial copper (Cu+) substitution with silver (Ag+) on the efficiency of flexible CZTSSe solar cells.
• To optimize silver doping concentration for improved photovoltaic properties.

Main Methods:

• Synthesis of (Cu1-xAgx)2ZnSn(S,Se)4 (CAZTSSe) thin films with varying Ag doping levels (x from 0 to 6%).
• Characterization of CAZTSSe thin films, including band gap (Eg) and grain size measurements.
• Analysis of the CAZTSSe/CdS heterojunction interface, including depletion width (Wd).
• Evaluation of photovoltaic performance, focusing on open-circuit voltage (Voc), open-circuit voltage deficit (Voc,def), and power conversion efficiency (PCE).

Main Results:

• Silver doping allows tuning of the CAZTSSe band gap (Eg), with a minimum Eg observed at x = 5%.
• Average grain size of the CAZTSSe absorber increased from 0.4 μm to 1.1 μm with Ag doping.
• Improved depletion width (Wd) at the CAZTSSe/CdS heterojunction was observed.
• Open-circuit voltage deficit (Voc,def) decreased from 915 mV to 848 mV, and band tailing was suppressed.
• Power conversion efficiency (PCE) increased from 4.34% (x = 0) to 6.24% (x = 4%).

Conclusions:

• Partial substitution of Cu+ with Ag+ is an effective strategy for enhancing the efficiency of flexible CZTSSe solar cells.
• Ag doping improves key photovoltaic parameters, including grain size, open-circuit voltage, and reduces voltage losses.
• Optimized Ag doping leads to significant improvements in the power conversion efficiency of CZTSSe-based solar devices.