New research conducted by researchers from China’s Southwest Petroleum University, the Chinese Academy of Sciences (CAS) and Chengdu-based PV manufacturer Tongwei suggests that the commercial success of two-terminal (2T) perovskite-silicon solar cells will depend more on geography and market conditions than on achieving efficiencies beyond current levels.
“Our work reframes tandem photovoltaics as a field-performance question, not only an efficiency race,” corresponding author Jian Yu told pv magazine. “Our model can guide spectrum-aware device design for different climates and market conditions before large-scale commercial rollout.”
He explained that 2T perovskite/silicon tandems stack a wide-bandgap perovskite cell on a silicon cell connected in series, so the whole device is governed by the lower-current sub-cell. 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.
“To quantify these effects, we 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,” Yu went on to say. “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.”
In the study “Challenges of two-terminal perovskite-silicon tandem solar cells operating under globally varying spectral conditions,” published in eScience Energy, the researchers 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.
They fabricated the 2T tandem cells by combining textured n-type Czochralski (CZ) silicon bottom cells with p-i-n perovskite top cells. The 200 μm silicon wafers were etched, textured with potassium hydroxide (KOH), and cleaned using standard RCA procedure and hydrofluoric acid (HF) treatments. Thin hydrogenated intrinsic amorphous silicon (i-a-Si:H) and doped hydrogenated nanocrystalline silicon (nc-Si:H) layers were deposited by plasma-enhanced chemical vapor deposition (PECVD) to form the silicon heterojunction structure. Tungsten-doped indium oxide (IWO) was added as the interconnection and rear-contact layers, followed by screen-printed silver and a magnesium fluoride (MgFₓ) back reflector.
The silicon cells were then laser-cut into 2 × 2 cm² substrates for tandem integration. For the top cells, [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (Me-4PACz) was spin-coated as the hole transport layer and annealed. A wide-bandgap cesium-formamidinium-methylammonium lead iodide-bromide (Cs₀.₀₅FA₀.₈MA₀.₁₅Pb(I₀.₇₅Br₀.₂₅)₃ perovskite layer was deposited using a one-step anti-solvent process.
The perovskite films were subsequently passivated with phenethylammonium bromide (PEABr) and ethylenediammonium diiodide (EDAI₂) before C₆₀ (buckminsterfullerene) and tin oxide (SnO₂) electron transport and buffer layers were added. Silver (Ag) electrodes were then deposited, followed by a MgFₓ anti-reflection coating to complete the tandem device.
The research team 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). The simulator spectra were measured with a fibre-optic spectrometer, while four solar cell samples fabricated in the same batch were characterized for external quantum efficiency (EQE). Theoretical short-circuit current density values were then calculated from the measured spectra and EQE data. Current deviations between repeated measurements were kept below 2% to minimize measurement uncertainty.
For outdoor conditions, they analyzed year-round spectral data from Haikou and Yancheng in China, Albuquerque in the United States, and Daqing in China. They calculated the spectral mismatch factor (MMF) for the perovskite top and silicon bottom sub-cells, as well as for single-junction tunnel oxide passivated contact (TOPCon) cells.
The scientists also 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 MMFs. 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. Because tandem modules are not yet commercially produced at scale, both technologies were initially assigned the same module price of $0.11/W, followed by a price-sensitivity analysis to determine how much of a premium tandem modules could command while maintaining LCOE parity.
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, meanwhile, 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. “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%,” they stated. “These results indicate that although 2 T tandem solar cells suffer from performance degradation due to spectral mismatch, their substantial efficiency advantage still offers overall economic benefits.”
Looking ahead, 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. “Future tandem commercialization should pair high-efficiency cells with climate-specific spectral evaluation,” Yu said.
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