Electron-Selective TiO2 Contact for Cu(In,Ga)Se2 Solar Cells.

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Physics

Background:

• Copper indium gallium selenide (CIGS) thin-film solar cells are a promising photovoltaic technology.
• Traditional CIGS solar cells often use cadmium sulfide (CdS) as a buffer layer, which poses toxicity concerns.
• Developing non-toxic, high-performance buffer layers is crucial for advancing CIGS solar cell technology.

Purpose of the Study:

• To investigate titanium dioxide (TiO2) as a non-toxic, n-type buffer layer for p-type CIGS absorber layers in thin-film solar cells.
• To evaluate the performance and stability of CIGS solar cells utilizing a TiO2 buffer layer compared to a CdS buffer layer.
• To understand the impact of TiO2's wide bandgap on photocurrent generation and parasitic absorption.

Main Methods:

• Amorphous TiO2 thin films were deposited using atomic layer deposition at low temperatures.
• CIGS solar cells with TiO2 buffer layers were fabricated and characterized.
• Performance metrics including short-circuit current density (Jsc), open-circuit voltage (Voc), and overall conversion efficiency were measured.
• Comparison was made with reference cells using CdS buffer layers.

Main Results:

• TiO2 thin films exhibited conformal coverage on the CIGS absorber layer.
• CIGS solar cells with TiO2 buffer layers achieved a higher Jsc (38.9 mA/cm²) compared to CdS (36.9 mA/cm²).
• The TiO2 buffer layer (bandgap 3.4 eV) resulted in reduced parasitic absorption, particularly in the UV spectrum, leading to improved photocurrent.
• Overall solar cell conversion efficiency increased from 9.5% to 9.9% with the TiO2 buffer.
• Optimized TiO2/CIGS solar cells demonstrated excellent long-term stability.

Conclusions:

• TiO2 is a viable and promising non-toxic alternative to CdS as a buffer layer for CIGS solar cells.
• The use of TiO2 offers performance advantages, including enhanced photocurrent and efficiency, without compromising open-circuit voltage.
• TiO2-based CIGS solar cells exhibit excellent long-term stability, making them attractive for future photovoltaic applications.