High-Efficiency CIGS Thin-Film Solar Cells: Highlights And Challenges

Thin-film photovoltaic (PV) modules of Cu(In,Ga)Se2 (CIGS) have the potential to reach cost-effective PV-generated electricity. The technology has transitioned from the laboratory to the market place. Pilot production and first-time manufacturing are ramping up to higher capacity and enjoying a flood of venture-capital funding. CIGS solar cells and modules have achieved 20% and 13.5% efficiencies, respectively. Even higher efficiencies from the laboratory and from the manufacturing line are only a matter of time. Manufacturing-line yield continues to improve and is surpassing 85% in some cases. Long-term stability has been demonstrated; however, some failures in the field have also been observed, emphasizing the critical need for understanding degradation mechanisms and packaging options. The device/module structure consists of substrate, base electrode, absorber, junction layer, top electrode, patterning steps for monolithic integration, and encapsulation. The monolithic integration of thin-film solar cells can lead to significant manufacturing cost reduction compared to crystalline Si. The CIGS module shares common structural elements with other thin film technologies such as CdTe and amorphous Si. In principle, this commonality should lead to similar manufacturing cost per unit area, and thus, the module efficiency becomes the discriminating factor that determines the cost per watt. The long-term potential of the technology requires continuous improvements in engineering-based challenges to find solutions to achieve targeted cost-effective module performance, and in-field durability. Some of the challenges are: in-situ process control and diagnostics, understanding degradation mechanisms, protection from water vapor, and innovation in high-speed processing and module design.