Engineering the “golden bridge”: Efficient tunnel junction design for next-generation all-perovskite tandem solar cells
2026-02-06
(Press-News.org)
WUHAN, CHINA — A research team from the Wuhan National Laboratory for Optoelectronics (WNLO) and the School of Optical and Electronic Information at Huazhong University of Science and Technology (HUST) has reported a new advancement in all-perovskite tandem solar cells. By utilizing quantitative Silvaco TCAD simulations, the team has elucidated the fundamental physics of the tunnel junction, providing a definitive design rule to overcome efficiency bottlenecks in all-perovskite tandem solar cells.
The Bottleneck: Unbalanced Charge Tunneling
All-perovskite tandem solar cells are a high-potential technology with theoretical efficiencies reaching approximately 45%. However, their practical performance is often limited by the tunnel junction—the critical interlayer that connects the top and bottom sub-cells. In these devices, the junction typically consists of a SnO2/metal/PEDOT:PSS structure.
The researchers found that the primary challenge lies in the intrinsic physical properties of the materials. In SnO2, electrons have an effective mass m* of approximately 0.2m0, whereas holes in PEDOT:PSS have a much higher effective mass of roughly 4.8m0. This discrepancy causes the hole tunneling probability to be four orders of magnitude lower than that of electrons, making hole transport the fundamental bottleneck within the tunnel junction.
The Breakthrough: The 5.1 eV Optimal Work Function
To address this imbalance, the team investigated how the work function (ΦM) of the interlayer metal dictates the energy barriers at the semiconductor interfaces. By scanning ΦM from 4.2 eV to 5.6 eV, the study identified a "sweet spot" at approximately 5.1 eV (representative of metals like Gold).
According to the findings:
Balanced Barriers: At ΦM ≈ 5.1 eV the barrier for holes at the HTL/metal interface is minimized to approximately 0.2 eV, while a moderate barrier of ~0.5 eV is maintained for electrons at the ETL/metal interface.
Minimal Resistance: This balanced configuration enables efficient bidirectional tunneling, reducing the equivalent series resistance of the tunnel junction to a remarkably low ~10⁻2 Ω·cm2.
Impact on Future Solar Technology
The study establishes that -driven band alignment is the central design principle for engineering high-performance tunnel junctions. These results provide quantitative guidance for selecting materials and alloys to advance all-perovskite TSCs toward their theoretical efficiency limits.
(Left) Schematic illustration of the all-perovskite tandem solar cell structure, highlighting the ETL/Metal/HTL tunnel junction1. (Middle) Equivalent circuit representation of the tandem device. (Right) Simulated equivalent series resistance of the tunnel junction as a function of the interlayer metal work function, showing the optimal resistance minimum near 5.1 eV.
The work entitled “Tunnel junction simulation of all-perovskite tandem solar cells” was published in Frontiers of Optoelectronics (published on Jan. 7, 2026). (Front. Optoelectron., 2026, 19(1): 2 DOI:10.2738/foe.2026.0002)
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[Press-News.org] Engineering the “golden bridge”: Efficient tunnel junction design for next-generation all-perovskite tandem solar cells
