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Purpose

Tandem photovoltaic (PV) devices such as Si/Copper Indium Gallium Selenide (CIGS) tandem architectures have the potential for higher conversion efficiency compared to single-junction silicon modules. This study evaluates the environmental performance of two emerging two-terminal (2T) Si/CIGS tandem architectures: circuitry 2T (C2T) and bonded 2T (B2T). The goal is to quantify their environmental impacts during manufacturing and identify key drivers and improvement opportunities through prospective life cycle assessment.

Methods

An innovative concept designed for tandem solar cells with a 2T approach based on two technologies: Silicon Heterojunction (SHJ) and high bandgap Cu(In, Ga)(Se, S)₂ (CIGS). A cradle-to-gate life cycle assessment was conducted for both C2T and B2T configurations. The study quantified the impacts per 1 kWh of generated electricity and conducted a life cycle impact assessment (LCIA) to identify the environmental hotspots of introduced technologies.

Results and discussion

The LCIA showed GWP values of 0.2203 and 0.1056 kg CO₂-eq/kWh for B2T and C2T, respectively. C2T demonstrated lower environmental impacts due to reduced energy requirements. Silicon solar cell production had the largest contribution across most impact categories. Replacing selenium with sulphur improved the results but the effect was small. Replacing ethyl-vinyl acetate with polyolefins also led to a minor improvement. The prospective analysis shows that under SSP2_RCP1.9 (targeting climate policy for carbon emissions reduction) and strong technological development, emissions fall to 0.014 kg CO₂ eq/kWh for B2T and 0.013 kg for C2T in 2050, representing a 94% and 88% reduction from present values in 2025, respectively.

Conclusions

Si/CIGS tandem technologies present strong potential for combining higher efficiencies with good environmental performance. C2T offers an advantage over B2T due to the absence of bonding materials. Sulphur-containing CIGS absorbers demonstrated the highest efficiency for the required high-bandgap cells, with improved environmental performance. However, several processes remain at low technology readiness levels, leaving room for efficiency improvements.

Recommendations

Further research should explore industrial-scale implementations, evaluate the impacts of energy sourcing by geography, and develop design strategies that balance efficiency gains with minimized environmental footprints. The study suggests that Si/CIGS tandem technologies can be a competitive option among emerging PV solutions, with GWP values falling within the wide range reported for single‑junction silicon PVs. Not only the full process line, but also individual components of the results of the study can be useful for implementation and roll-out. Future research should focus on optimizing material use and reducing process energy consumption without compromising device efficiency.