Study Suggests Two-Terminal Perovskite-Silicon Tandems May Not Deliver Optimal Performance in All Geographies

The commercial success of two-terminal perovskite-silicon solar cells may depend more on geography and market conditions than on achieving high efficiencies, according to new research.

Researchers from China's Southwest Petroleum University, the Chinese Academy of Sciences (CAS), and Chengdu-based PV manufacturer Tongwei conducted a study that reframed tandem photovoltaics as a field-performance question, rather than just an efficiency race. The study's corresponding author, Jian Yu, explained that two-terminal perovskite/silicon tandems stack a wide-bandgap perovskite cell on a silicon cell connected in series, making the whole device governed by the lower-current sub-cell.

Yu noted that maximum output is reached only when the two sub-cells are current matched, but outdoor spectra continuously shift with cloud cover, air mass, atmospheric absorption, water vapor, season, and geography, making standard test conditions an incomplete guide to real-world performance.

The researchers fabricated 2T perovskite-silicon tandem cells with a champion efficiency of 32.85% and used a tunable-spectrum solar simulator to reproduce blue-rich and red-rich conditions. The measurements showed current mismatch of 4.98% and 4.32% under blue-rich and red-rich spectra, respectively, with short-circuit current density and efficiency following the lower-current sub-cell.

The study emphasized that while the effects of spectral variations on 2T tandem solar cells are well known, relatively few studies have assessed their performance under real-world outdoor spectral conditions, especially across different climate zones.

The researchers used a tunable-spectrum steady-state light-emitting diode (LED) solar simulator to reproduce different spectral distributions within the 3A+ classification range under standard test conditions (STC). They also analyzed year-round spectral data from Haikou and Yancheng in China, Albuquerque in the United States, and Daqing in China.

The scientists used PVsyst to simulate the annual energy yield of 100 kW PV systems in the four locations, adjusting monthly output for tandem and single-junction cells using the respective spectral mismatch factors. They then calculated the levelized cost of electricity (LCOE), assuming the two technologies had identical operating characteristics apart from their spectral response to isolate the impact of spectral mismatch.

The laboratory tests showed that 2T tandem cells suffer current mismatch when exposed to spectra that differ from standard illumination conditions. Under blue-rich conditions, the perovskite top cell generated more current, while red-rich spectra favored the silicon bottom cell. Outdoor measurements confirmed that spectral variations are continuous and can substantially affect tandem-cell performance, particularly under cloudy conditions.

Year-round data from Haikou, Albuquerque, Yancheng, and Daqing showed that outdoor spectra rarely match standard conditions, resulting in persistent current mismatch between the sub-cells. The PVsyst simulations showed that spectral effects reduced annual tandem energy yields relative to single-junction cells by 1.10% in Haikou, 3.25% in Albuquerque, 0.77% in Yancheng, and 1.84% in Daqing.

Despite these losses, tandem modules delivered 8.74% to 11.16% higher annual energy yields per unit area because of their higher efficiency and power density. The levelized cost of electricity (LCOE) for tandems was found to be lower in Haikou, Yancheng, and Daqing, but 0.87% higher in Albuquerque, where spectral losses were greatest.

The researchers concluded that tandem economics depend strongly on location, with allowable module price premiums ranging from -4% in Albuquerque to 7% in Yancheng. They stated that a 1.59% reduction in LCOE was achieved for tandem cells through improved land-use efficiency and DC-side balance of system savings, thereby enabling a potential price premium of up to 7%.

The researchers aim to extend the spectral assessment framework to more climate zones and device architectures, and to combine it with temperature- and degradation-related modeling for more complete outdoor performance prediction. They suggest that future tandem commercialization should pair high-efficiency cells with climate-specific spectral evaluation.

## Study Methodology

The researchers fabricated 2T perovskite-silicon tandem cells with a champion efficiency of 32.85% and used a tunable-spectrum solar simulator to reproduce blue-rich and red-rich conditions. They also analyzed year-round spectral data from Haikou and Yancheng in China, Albuquerque in the United States, and Daqing in China.

## Results

The laboratory tests showed that 2T tandem cells suffer current mismatch when exposed to spectra that differ from standard illumination conditions. Under blue-rich conditions, the perovskite top cell generated more current, while red-rich spectra favored the silicon bottom cell. Outdoor measurements confirmed that spectral variations are continuous and can substantially affect tandem-cell performance, particularly under cloudy conditions.

| Location | Spectral Mismatch Factor (SMF) | | --- | --- | | Haikou | 1.10% | | Albuquerque | 3.25% | | Yancheng | 0.77% | | Daqing | 1.84% |

## Conclusion

The researchers concluded that tandem economics depend strongly on location, with allowable module price premiums ranging from -4% in Albuquerque to 7% in Yancheng. They stated that a 1.59% reduction in LCOE was achieved for tandem cells through improved land-use efficiency and DC-side balance of system savings, thereby enabling a potential price premium of up to 7%.