Researchers from the National Laboratory of the Rockies in the U.S. have formulated a comprehensive performance measurement framework for three-terminal (3-T) and four-terminal (4-T) tandem solar cells.
“Our work introduces the first comprehensive performance measurement framework specifically for three-terminal (3-T) and four-terminal (4-T) tandem solar cells, including perovskite-based devices,” Tao Song, corresponding author of the research told pv magazine, noting that there is a need for reliable and standardized performance-measurements for emerging multi-terminal tandems 3-T and 4-T tandem designs. “We demonstrated practical, validated approaches to ensure that reported efficiencies are accurate, reproducible, and comparable across laboratories and industry,” said Song.
The interest in 3-T and 4-T devices is driven by the potential to reduce subcell current-matching constraints, higher device energy yields, and as an alternative path for combining emerging PV materials like perovskites with established silicon material combinations, such as perovskites and silicon or perovskites and cadmium telluride (CdTe), according to the study.
The researchers illustrated the methods with three different multi-terminal cell configurations, two 3-T devices and one 4-T device. One 3-T was a perovskite/interdigitated-back-contact (IBC) silicon device and the other was a gallium indium phosphide (GaInP)/gallium arsenide (GaAs) device. The 4T device was a GaAs top cell with an IBC silicon bottom cell.
For 3-T tandems, the researchers indicated a straightforward protocol if both subcells are fast response types. But for devices with slow-responding subcells, such as those made with a perovskite absorber, two steady-state methods were described: (i) two-dimensional maximum power point tracking (MPPT) for both subcells, and (ii) a hybrid method combining MPPT on one subcell with an asymptotic stabilized maximum power (PMAX) scan on the other. “Both approaches yield equivalent results but differ in measurement time,” noted the researchers.
For 4-T tandems, the team described two I-V measurement approaches, either synchronized scans with spectrum adjustment or sequential scans with individual irradiance adjustment for each subcell.
“When slow-responding subcells are involved, they must be measured using steady-state methods, while fast-response subcells can be characterized with conventional I–V scans,” explained the researchers, adding that in cases where luminescent coupling exists between subcells, the non-tested subcell must be held at its PMAX “using a proper load resistor to ensure accurate determination of the combined output.”
“We expect this framework will help shape future International Electrotechnical Commission (IEC) and American Society for Testing and Materials (ASTM) standards for multi-terminal tandem devices,” said Song.
Noting that it adapts to both fast and slow-responding materials to properly account for electrical and optical coupling effects between subcells, Song said that the framework is “broadly applicable, not only to perovskite-based tandems, but also to other multi-terminal solar technologies like III–V, CdTe and silicon-based tandems.”
In the conclusion of the study, the team noted that not all research laboratories have access to spectrum-tuning hardware and synchronized scan capabilities. Without such tools, measurement limitations can introduce “non-trivial measurable errors.” As a result, third party testing to establish records and accurate baseline measurements was recommended.
For other cases, a simpler protocol was provided with the caveat that the measurement limitations and potential sources of error should be clearly documented and reported.
“The next step is broader adoption and standardization of these measurement practices. As tandem devices scale toward manufacturing, consistent and trustworthy performance rating will be essential,” said Song. The group is now extending these methods to industrial-scale wafers and modules, supporting the development of future international standards for tandem PV testing.
The research work is detailed in “Performance measurement of emerging 3- and 4-terminal tandem solar cells,” published by EES Solar. A team from Centre suisse d'électronique et de microtechnique (CSEM) also participated in the study.
Image:
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.
By submitting this form you agree to pv magazine using your data for the purposes of publishing your comment.
Your personal data will only be disclosed or otherwise transmitted to third parties for the purposes of spam filtering or if this is necessary for technical maintenance of the website. Any other transfer to third parties will not take place unless this is justified on the basis of applicable data protection regulations or if pv magazine is legally obliged to do so.
You may revoke this consent at any time with effect for the future, in which case your personal data will be deleted immediately. Otherwise, your data will be deleted if pv magazine has processed your request or the purpose of data storage is fulfilled.
Further information on data privacy can be found in our Data Protection Policy.