Revolutionizing Solar Cell Efficiency: A New Design for Tunnel Junctions
WUHAN, CHINA — Researchers from the Wuhan National Laboratory for Optoelectronics (WNLO) and the School of Optical and Electronic Information at Huazhong University of Science and Technology (HUST) have made significant strides in the development of all-perovskite tandem solar cells. Their recent work employs advanced Silvaco TCAD simulations to delve into the underlying physics of tunnel junctions, ultimately establishing a clear set of design guidelines aimed at overcoming the efficiency limitations currently faced by these innovative solar cells.
The Challenge: Imbalanced Charge Tunneling
All-perovskite tandem solar cells hold tremendous promise, with theoretical efficiency estimates soaring to around 45%. Yet, in practical applications, their performance is frequently hindered by the tunnel junction—an essential layer that links the upper and lower sub-cells. Typically, this junction is composed of a structure featuring SnO2, a metal, and PEDOT:PSS.
The research team identified a major obstacle rooted in the inherent physical characteristics of the materials involved. For instance, in the case of SnO2, electrons exhibit an effective mass (m*) of about 0.2 times that of a free electron (m0), while holes within PEDOT:PSS showcase a significantly higher effective mass, roughly 4.8m0. This stark difference leads to a tunneling probability for holes that is four magnitudes lower than that for electrons, ultimately rendering hole transport the critical bottleneck within the tunnel junction.
The Discovery: Finding the Sweet Spot at 5.1 eV
To remedy this imbalance, the researchers explored how the work function (ΦM) of the interlayer metal influences the energy barriers present at the semiconductor interfaces. Through a careful examination of ΦM ranging from 4.2 eV to 5.6 eV, they pinpointed an optimal value of approximately 5.1 eV, which correlates with metals such as Gold.
Their findings revealed several crucial insights:
1. Optimized Barriers: At the work function of ΦM ≈ 5.1 eV, the barrier for hole movement at the high-temperature layer (HTL)/metal interface is reduced to about 0.2 eV, while the barrier for electrons at the electron transport layer (ETL)/metal interface remains moderately higher at around 0.5 eV.
2. Reduced Resistance: This balanced setup allows for efficient bidirectional tunneling, leading to an astonishing drop in the equivalent series resistance of the tunnel junction to approximately 0.01 Ω·cm².
Implications for Future Solar Technologies
This research underscores the significance of band alignment driven by work function as the core principle for crafting high-efficiency tunnel junctions. The insights gained provide essential guidance for selecting suitable materials and alloys, bringing all-perovskite tandem solar cells closer to achieving their theoretical efficiency potentials.
(Left) A schematic illustration depicts the structure of the all-perovskite tandem solar cell, with an emphasis on the ETL/Metal/HTL tunnel junction. (Middle) An equivalent circuit diagram represents the tandem device's functioning. (Right) A simulation graph showcases the equivalent series resistance of the tunnel junction relative to the interlayer metal work function, indicating the optimal resistance minimum near 5.1 eV.
The study titled "Tunnel junction simulation of all-perovskite tandem solar cells" was published in Frontiers of Optoelectronics on January 7, 2026. For more detailed insights, you can visit the publication here.
/Public Release. The information provided in this article reflects the views of the original authors and may be subject to change. Mirage.News does not endorse any particular stance or viewpoint; all opinions and conclusions expressed are strictly those of the authors. For the full content, click here.
